WEBVTT 00:00:00.000 --> 00:00:01.991 align:middle line:90% [SQUEAKING] 00:00:01.991 --> 00:00:03.979 align:middle line:90% [RUSTLING] 00:00:03.979 --> 00:00:05.967 align:middle line:90% [CLICKING] 00:00:05.967 --> 00:00:17.700 align:middle line:90% 00:00:17.700 --> 00:00:18.600 align:middle line:90% PROFESSOR: So OK. 00:00:18.600 --> 00:00:20.720 align:middle line:84% So in this lecture here, we are going 00:00:20.720 --> 00:00:23.240 align:middle line:84% to continue our discussion about, essentially, glass 00:00:23.240 --> 00:00:24.560 align:middle line:90% viscosity. 00:00:24.560 --> 00:00:26.680 align:middle line:84% I'm starting out with showing you this slide here 00:00:26.680 --> 00:00:29.080 align:middle line:84% that shows the different viscosity reference 00:00:29.080 --> 00:00:31.160 align:middle line:84% points that are of importance when 00:00:31.160 --> 00:00:33.960 align:middle line:90% it comes to glass processing. 00:00:33.960 --> 00:00:38.560 align:middle line:84% So horizontal axis is basically the viscosity in log scale. 00:00:38.560 --> 00:00:40.920 align:middle line:84% And there are a few important viscosity points 00:00:40.920 --> 00:00:42.680 align:middle line:90% that I want to highlight here. 00:00:42.680 --> 00:00:44.920 align:middle line:84% First one is being this working point. 00:00:44.920 --> 00:00:49.120 align:middle line:84% It corresponds to a viscosity of 10 to the 3 Pascal-second. 00:00:49.120 --> 00:00:51.520 align:middle line:84% So below the working point, the glass 00:00:51.520 --> 00:00:54.420 align:middle line:84% basically flows just like a regular fluid, 00:00:54.420 --> 00:00:55.685 align:middle line:90% so like water-like. 00:00:55.685 --> 00:00:57.560 align:middle line:84% So it becomes very difficult to actually hold 00:00:57.560 --> 00:01:00.200 align:middle line:84% any shape for a given period of time. 00:01:00.200 --> 00:01:03.200 align:middle line:84% And that's why below that it's pretty much just considered 00:01:03.200 --> 00:01:04.700 align:middle line:90% like a fluid. 00:01:04.700 --> 00:01:06.520 align:middle line:90% It's a super cool liquid. 00:01:06.520 --> 00:01:10.280 align:middle line:84% So you need to have a sufficiently high viscosity 00:01:10.280 --> 00:01:12.140 align:middle line:84% to enable any kind of glass processing. 00:01:12.140 --> 00:01:14.240 align:middle line:84% So that's what the working point means. 00:01:14.240 --> 00:01:16.440 align:middle line:84% The viscosity has to be higher than the working 00:01:16.440 --> 00:01:19.720 align:middle line:90% point for actual glass shaping. 00:01:19.720 --> 00:01:23.320 align:middle line:84% Then the next part is called softening point. 00:01:23.320 --> 00:01:25.920 align:middle line:84% So if you go above this softening point, which 00:01:25.920 --> 00:01:31.040 align:middle line:84% corresponds to 10 to the 6.6 Pascal-second viscosity value, 00:01:31.040 --> 00:01:33.840 align:middle line:84% then the glass melts, becomes so stiff 00:01:33.840 --> 00:01:37.400 align:middle line:84% that it becomes difficult to actually start to deform it. 00:01:37.400 --> 00:01:41.100 align:middle line:84% So between this working point and softening point, 00:01:41.100 --> 00:01:46.080 align:middle line:84% this is what's defined as the working range for glass melt. So 00:01:46.080 --> 00:01:48.080 align:middle line:84% just to give you an intuitive example about what 00:01:48.080 --> 00:01:50.680 align:middle line:84% the viscosity is like, I have actually marked here 00:01:50.680 --> 00:01:54.580 align:middle line:84% this little arrow right in the middle of the working range. 00:01:54.580 --> 00:01:57.960 align:middle line:84% This is the typical viscosity of chewing gum. 00:01:57.960 --> 00:02:00.240 align:middle line:84% So intuitively, the glass will behave 00:02:00.240 --> 00:02:03.040 align:middle line:84% like a chewing gum within that viscosity range, 00:02:03.040 --> 00:02:05.278 align:middle line:84% and you can easily essentially shape it, change it 00:02:05.278 --> 00:02:07.320 align:middle line:84% to any kind of geometry, and you'll hold it there 00:02:07.320 --> 00:02:10.039 align:middle line:84% for some period of time that allows you to essentially 00:02:10.039 --> 00:02:11.900 align:middle line:90% sustain the shape you want. 00:02:11.900 --> 00:02:14.580 align:middle line:84% And once you cool it down, the viscosity increases, 00:02:14.580 --> 00:02:17.880 align:middle line:84% then you're sort of freezing the geometry you need. 00:02:17.880 --> 00:02:19.265 align:middle line:90% So I have listed here-- 00:02:19.265 --> 00:02:20.640 align:middle line:84% in the next lecture, we are going 00:02:20.640 --> 00:02:22.160 align:middle line:84% to talk about different glass-shaping techniques, 00:02:22.160 --> 00:02:22.990 align:middle line:90% specifically. 00:02:22.990 --> 00:02:25.240 align:middle line:84% But you can see there are a lot of these glass-shaping 00:02:25.240 --> 00:02:27.560 align:middle line:84% techniques, they all have a viscosity value that 00:02:27.560 --> 00:02:29.220 align:middle line:90% falls within this window here. 00:02:29.220 --> 00:02:31.872 align:middle line:90% 00:02:31.872 --> 00:02:35.440 align:middle line:84% The next reference point is annealing point. 00:02:35.440 --> 00:02:36.960 align:middle line:84% So annealing point corresponds to 10 00:02:36.960 --> 00:02:39.380 align:middle line:84% to the 12 Pascal-second viscosity, 00:02:39.380 --> 00:02:42.900 align:middle line:84% which basically coincides with the definition of Tg. 00:02:42.900 --> 00:02:46.560 align:middle line:84% So annealing point is basically glass transition temperature. 00:02:46.560 --> 00:02:50.920 align:middle line:84% Annealing point is where, once the glass product is made, 00:02:50.920 --> 00:02:54.800 align:middle line:84% this is the temperature where you do a post-shaping annealing 00:02:54.800 --> 00:02:58.230 align:middle line:90% to release any internal stress. 00:02:58.230 --> 00:02:58.910 align:middle line:90% OK. 00:02:58.910 --> 00:03:01.950 align:middle line:84% So at the annealing point, microscopic changes 00:03:01.950 --> 00:03:03.050 align:middle line:90% can still take place. 00:03:03.050 --> 00:03:05.790 align:middle line:84% You can relax any internal stress and strain, 00:03:05.790 --> 00:03:10.030 align:middle line:84% but macroscopic shape change no longer takes place. 00:03:10.030 --> 00:03:11.870 align:middle line:84% Because it requires low viscosity 00:03:11.870 --> 00:03:14.820 align:middle line:84% value to induce macroscopic movement. 00:03:14.820 --> 00:03:17.070 align:middle line:84% So that's basically the temperature where you actually 00:03:17.070 --> 00:03:19.550 align:middle line:84% anneal the glass products without distorting the shape 00:03:19.550 --> 00:03:23.030 align:middle line:84% while ensuring that they don't have any kind of internal stress 00:03:23.030 --> 00:03:23.742 align:middle line:90% there. 00:03:23.742 --> 00:03:25.450 align:middle line:84% Now, if you look at this viscosity value, 00:03:25.450 --> 00:03:29.240 align:middle line:84% by the way, for pitch, which is a very viscous fluid, 00:03:29.240 --> 00:03:30.990 align:middle line:84% you see this viscosity, you can measure it 00:03:30.990 --> 00:03:33.282 align:middle line:84% from the pitch drop experiment, it's of the order of 10 00:03:33.282 --> 00:03:33.950 align:middle line:90% to the 8. 00:03:33.950 --> 00:03:37.130 align:middle line:84% So 10 to the 12 is very high viscosity. 00:03:37.130 --> 00:03:39.670 align:middle line:84% That's why you don't see any kind of macroscopic deformation 00:03:39.670 --> 00:03:41.350 align:middle line:90% there. 00:03:41.350 --> 00:03:47.990 align:middle line:84% Now, finally, when the glass exits the annealing furnace, 00:03:47.990 --> 00:03:51.110 align:middle line:84% its viscosity will be higher than the straining point. 00:03:51.110 --> 00:03:54.310 align:middle line:84% So straining point is the viscosity value where, 00:03:54.310 --> 00:03:58.270 align:middle line:84% above which you don't even have microstructural relaxation. 00:03:58.270 --> 00:04:00.990 align:middle line:84% So annealing essentially takes place between the annealing 00:04:00.990 --> 00:04:02.290 align:middle line:90% point and straining point. 00:04:02.290 --> 00:04:06.690 align:middle line:84% This is where you can have a strain-stress relaxation. 00:04:06.690 --> 00:04:09.710 align:middle line:84% So we'll see this reference chart again 00:04:09.710 --> 00:04:13.042 align:middle line:84% when we actually talk about glass processing, in fact, 00:04:13.042 --> 00:04:15.310 align:middle line:84% in this lecture, the later part of this lecture. 00:04:15.310 --> 00:04:17.510 align:middle line:84% But these are the important reference points 00:04:17.510 --> 00:04:22.989 align:middle line:84% that's important to know in glass processing. 00:04:22.989 --> 00:04:27.630 align:middle line:84% So to control the viscosity, we have a very simple knob 00:04:27.630 --> 00:04:28.850 align:middle line:90% here for glass materials. 00:04:28.850 --> 00:04:30.790 align:middle line:84% You can simply just change temperature. 00:04:30.790 --> 00:04:34.770 align:middle line:84% From the previous slide, when we talked about the Angell's plot, 00:04:34.770 --> 00:04:36.612 align:middle line:84% we know that the viscosity changes 00:04:36.612 --> 00:04:39.070 align:middle line:84% by many orders of magnitude because its thermally activated 00:04:39.070 --> 00:04:40.510 align:middle line:90% phenomena. 00:04:40.510 --> 00:04:42.290 align:middle line:90% So yeah. 00:04:42.290 --> 00:04:44.430 align:middle line:84% So then it gives us a very easy way 00:04:44.430 --> 00:04:46.430 align:middle line:84% to essentially tune viscosity and push 00:04:46.430 --> 00:04:48.730 align:middle line:84% to the desired value for specific processes there. 00:04:48.730 --> 00:04:51.150 align:middle line:84% So then, depending on the specific kind 00:04:51.150 --> 00:04:53.330 align:middle line:84% of amorphous material you're looking at here, 00:04:53.330 --> 00:04:55.310 align:middle line:84% they can exhibit different kinds of behavior 00:04:55.310 --> 00:04:56.710 align:middle line:90% in terms of viscosity there. 00:04:56.710 --> 00:04:58.270 align:middle line:90% Specifically polymers. 00:04:58.270 --> 00:05:03.025 align:middle line:84% So for amorphous polymers or-- lots of polymers, 00:05:03.025 --> 00:05:04.650 align:middle line:84% they are actually not purely amorphous. 00:05:04.650 --> 00:05:07.870 align:middle line:84% They are a mixture of amorphous phase and crystalline phase. 00:05:07.870 --> 00:05:10.910 align:middle line:84% But either way, as long as it contains amorphous phase, then 00:05:10.910 --> 00:05:14.310 align:middle line:84% from a rheological perspective, they all behave pretty similar. 00:05:14.310 --> 00:05:17.950 align:middle line:84% They exhibit this kind of a temperature-dependent viscosity 00:05:17.950 --> 00:05:20.990 align:middle line:84% curve, like what I'm showing on the left-hand side here. 00:05:20.990 --> 00:05:24.110 align:middle line:84% At low temperature, they basically 00:05:24.110 --> 00:05:25.870 align:middle line:90% behave like hard plastic. 00:05:25.870 --> 00:05:26.950 align:middle line:90% They don't easily deform. 00:05:26.950 --> 00:05:29.670 align:middle line:90% It's rigid and stiff. 00:05:29.670 --> 00:05:32.070 align:middle line:84% As you start to heat it up, you go into, essentially, 00:05:32.070 --> 00:05:35.910 align:middle line:90% this sort of rubbery state. 00:05:35.910 --> 00:05:39.850 align:middle line:84% This is beyond, basically, the glass transition temperature. 00:05:39.850 --> 00:05:44.230 align:middle line:84% The molecular chains, they start to have enough energy 00:05:44.230 --> 00:05:45.272 align:middle line:90% to move around. 00:05:45.272 --> 00:05:46.730 align:middle line:84% They can change their conformation, 00:05:46.730 --> 00:05:48.270 align:middle line:90% they can move past each other. 00:05:48.270 --> 00:05:51.390 align:middle line:84% So then they go into a state that behaves more like rubber. 00:05:51.390 --> 00:05:55.150 align:middle line:84% So that's a rubbery state in the polymer language, 00:05:55.150 --> 00:05:56.590 align:middle line:90% typically what people call it. 00:05:56.590 --> 00:05:58.670 align:middle line:84% And then if you continue to heat it up, 00:05:58.670 --> 00:06:01.890 align:middle line:84% eventually it becomes a liquid, glass-forming liquid. 00:06:01.890 --> 00:06:06.730 align:middle line:90% 00:06:06.730 --> 00:06:12.430 align:middle line:84% So you can engineer this kind of viscosity behavior 00:06:12.430 --> 00:06:14.330 align:middle line:84% like changing microstructure of the polymers. 00:06:14.330 --> 00:06:19.910 align:middle line:84% So for example, if you want to change the Tg in polymers, so 00:06:19.910 --> 00:06:23.950 align:middle line:84% that you change the softening temperature, 00:06:23.950 --> 00:06:26.810 align:middle line:84% you can add some stiff chemical groups like benzene. 00:06:26.810 --> 00:06:28.650 align:middle line:90% Benzene is a ring. 00:06:28.650 --> 00:06:29.570 align:middle line:90% It's a planar ring. 00:06:29.570 --> 00:06:30.703 align:middle line:90% It doesn't easily deform. 00:06:30.703 --> 00:06:32.870 align:middle line:84% So if you add benzenes into the polymer chain there, 00:06:32.870 --> 00:06:34.870 align:middle line:84% it increases the stiffness of the polymer chain. 00:06:34.870 --> 00:06:37.410 align:middle line:84% It becomes much more difficult to deform it. 00:06:37.410 --> 00:06:39.910 align:middle line:84% And as a result, the viscosity is going to rise. 00:06:39.910 --> 00:06:42.350 align:middle line:84% And because Tg is defined with respect to viscosity, 00:06:42.350 --> 00:06:45.230 align:middle line:84% essentially, that means you also raise the Tg. 00:06:45.230 --> 00:06:49.070 align:middle line:84% So that's one way to essentially change the Tg. 00:06:49.070 --> 00:06:51.310 align:middle line:84% If you want to decrease Tg, on the other hand, what 00:06:51.310 --> 00:06:52.870 align:middle line:84% you can do-- typically, people put 00:06:52.870 --> 00:06:54.910 align:middle line:90% in what's called a plasticizer. 00:06:54.910 --> 00:06:56.790 align:middle line:84% Plasticizer, these are essentially 00:06:56.790 --> 00:06:58.990 align:middle line:90% small molecule solvents. 00:06:58.990 --> 00:07:02.110 align:middle line:84% They go into the polymer network and they 00:07:02.110 --> 00:07:06.350 align:middle line:90% serve as molecular lubricants. 00:07:06.350 --> 00:07:09.350 align:middle line:84% They decrease this internal friction between the polymer 00:07:09.350 --> 00:07:12.190 align:middle line:84% chains, so that it becomes a lot easier to move around. 00:07:12.190 --> 00:07:14.870 align:middle line:84% And the result is that you can actually 00:07:14.870 --> 00:07:17.828 align:middle line:84% decrease Tg in this case, which could be useful 00:07:17.828 --> 00:07:19.870 align:middle line:84% if you're trying to do some processing at greatly 00:07:19.870 --> 00:07:22.110 align:middle line:90% reduced temperatures. 00:07:22.110 --> 00:07:26.390 align:middle line:84% One example of this kind of a [INAUDIBLE] low-Tg polymer 00:07:26.390 --> 00:07:29.850 align:middle line:90% is this kind of polymer there. 00:07:29.850 --> 00:07:31.350 align:middle line:84% You can actually buy it from Amazon. 00:07:31.350 --> 00:07:33.710 align:middle line:84% It has a glass transition temperature 00:07:33.710 --> 00:07:36.710 align:middle line:84% that's engineered to be around 70 degrees Celsius. 00:07:36.710 --> 00:07:40.510 align:middle line:84% So if you put it into hot water, it softens. 00:07:40.510 --> 00:07:43.390 align:middle line:84% It becomes something you can mold by your hand 00:07:43.390 --> 00:07:44.930 align:middle line:90% to any kind of geometry. 00:07:44.930 --> 00:07:46.930 align:middle line:84% But when it cools down back to room temperature, 00:07:46.930 --> 00:07:48.510 align:middle line:90% it becomes stiff again. 00:07:48.510 --> 00:07:50.410 align:middle line:84% This you can search for on Amazon. 00:07:50.410 --> 00:07:52.315 align:middle line:90% This is called foam cards. 00:07:52.315 --> 00:07:54.190 align:middle line:84% So this would be quite handy if you're trying 00:07:54.190 --> 00:07:55.610 align:middle line:90% to just make something quickly. 00:07:55.610 --> 00:07:58.350 align:middle line:84% And again, this all goes into how you actually 00:07:58.350 --> 00:08:01.070 align:middle line:84% engineer the polymer Tg, so that you can change its softening 00:08:01.070 --> 00:08:02.350 align:middle line:90% behavior in this case. 00:08:02.350 --> 00:08:05.910 align:middle line:90% So that's for organic polymers. 00:08:05.910 --> 00:08:09.030 align:middle line:84% Now, for inorganic glasses, in this slide 00:08:09.030 --> 00:08:11.510 align:middle line:84% here, I'm summarizing the temperature dependence 00:08:11.510 --> 00:08:13.630 align:middle line:84% of viscosity for many different compositions 00:08:13.630 --> 00:08:15.050 align:middle line:90% of inorganic glasses. 00:08:15.050 --> 00:08:18.430 align:middle line:84% The general rule of thumb is that viscosity 00:08:18.430 --> 00:08:20.390 align:middle line:84% is a parameter that links closely 00:08:20.390 --> 00:08:21.970 align:middle line:90% with the network connectivity. 00:08:21.970 --> 00:08:25.070 align:middle line:90% 00:08:25.070 --> 00:08:28.310 align:middle line:84% And intuitively, it makes a lot of sense 00:08:28.310 --> 00:08:30.470 align:middle line:84% if you have a network that's connected together 00:08:30.470 --> 00:08:32.590 align:middle line:84% by many rigid chemical bonds that 00:08:32.590 --> 00:08:34.289 align:middle line:90% is very difficult to deform it. 00:08:34.289 --> 00:08:36.350 align:middle line:84% And therefore, you should have a high viscosity. 00:08:36.350 --> 00:08:39.429 align:middle line:84% So typically, high network connectivity 00:08:39.429 --> 00:08:45.230 align:middle line:84% would correspond to high viscosity and hence high Tg. 00:08:45.230 --> 00:08:47.310 align:middle line:84% So if you look at this plot here, 00:08:47.310 --> 00:08:55.820 align:middle line:84% on the upper right corner, this orange curve, 00:08:55.820 --> 00:09:00.940 align:middle line:84% this corresponds to a silica glass, just SiO2. 00:09:00.940 --> 00:09:06.520 align:middle line:84% Now, you see, for SiO2, its working range, in fact, 00:09:06.520 --> 00:09:07.820 align:middle line:90% is extremely high. 00:09:07.820 --> 00:09:10.420 align:middle line:84% It's beyond this chart here, its working range. 00:09:10.420 --> 00:09:13.740 align:middle line:84% So that's part of the reason why silica glass 00:09:13.740 --> 00:09:16.280 align:middle line:90% products is much more rare. 00:09:16.280 --> 00:09:17.920 align:middle line:84% It's actually a lot more expensive. 00:09:17.920 --> 00:09:20.620 align:middle line:84% Typical glass workshops, they cannot work with silica glass, 00:09:20.620 --> 00:09:23.078 align:middle line:84% because their furnaces are not at a high enough temperature 00:09:23.078 --> 00:09:25.860 align:middle line:84% to just soften silica glass so they can process it in different 00:09:25.860 --> 00:09:27.220 align:middle line:90% shapes. 00:09:27.220 --> 00:09:30.027 align:middle line:84% Now, the next group of glasses we're going to look at here, 00:09:30.027 --> 00:09:31.860 align:middle line:84% look at these two curves here, this blue one 00:09:31.860 --> 00:09:33.300 align:middle line:90% and this green one. 00:09:33.300 --> 00:09:35.700 align:middle line:84% These are essentially borosilicate glasses. 00:09:35.700 --> 00:09:37.100 align:middle line:84% So you notice that they still lie 00:09:37.100 --> 00:09:38.660 align:middle line:84% above the conventional soda-lime. 00:09:38.660 --> 00:09:41.160 align:middle line:84% This black line is a typical soda-lime-- windowpane glasses. 00:09:41.160 --> 00:09:43.280 align:middle line:84% So we have already talked about it. 00:09:43.280 --> 00:09:46.600 align:middle line:84% When you add boron into the glass network, 00:09:46.600 --> 00:09:48.855 align:middle line:84% you can trigger this P3 to P4 conversion, 00:09:48.855 --> 00:09:50.980 align:middle line:84% and therefore, you essentially increase the network 00:09:50.980 --> 00:09:51.860 align:middle line:90% connectivity. 00:09:51.860 --> 00:09:54.980 align:middle line:84% And that's why borosilicate glasses, 00:09:54.980 --> 00:09:57.940 align:middle line:84% they tend to have a higher viscosity compared 00:09:57.940 --> 00:09:59.233 align:middle line:90% to soda-lime glasses. 00:09:59.233 --> 00:10:01.400 align:middle line:84% In other words, if you look at all the temperatures, 00:10:01.400 --> 00:10:03.180 align:middle line:84% all the viscosity reference points-- 00:10:03.180 --> 00:10:08.060 align:middle line:90% working range, softening point-- 00:10:08.060 --> 00:10:12.020 align:middle line:84% borosilicate glasses tend to have much higher temperatures 00:10:12.020 --> 00:10:13.560 align:middle line:90% compared to soda-lime glasses. 00:10:13.560 --> 00:10:17.180 align:middle line:90% 00:10:17.180 --> 00:10:20.660 align:middle line:84% And that's why, in fact, it's more challenging for glass 00:10:20.660 --> 00:10:23.020 align:middle line:84% workshops to actually process borosilicate glasses. 00:10:23.020 --> 00:10:26.780 align:middle line:84% And then finally, you see that if you add a lot of alkaline, 00:10:26.780 --> 00:10:28.380 align:middle line:84% then this is the way you actually 00:10:28.380 --> 00:10:30.255 align:middle line:84% use to actually decrease network connectivity 00:10:30.255 --> 00:10:32.660 align:middle line:84% and hence the glass processing temperatures. 00:10:32.660 --> 00:10:35.660 align:middle line:90% 00:10:35.660 --> 00:10:37.220 align:middle line:84% Now, by adding alkaline, as I said, 00:10:37.220 --> 00:10:40.460 align:middle line:84% you can decrease the network connectivity and hence 00:10:40.460 --> 00:10:41.580 align:middle line:90% the viscosity. 00:10:41.580 --> 00:10:43.900 align:middle line:84% One very important fact I also want to mention here 00:10:43.900 --> 00:10:45.900 align:middle line:84% is that if you-- instead of adding just one 00:10:45.900 --> 00:10:48.820 align:middle line:84% kind of alkaline atom-- if you add two types or more 00:10:48.820 --> 00:10:51.620 align:middle line:84% than two types of alkali atoms simultaneously, 00:10:51.620 --> 00:10:55.700 align:middle line:84% the depression of the viscosity becomes even more significant. 00:10:55.700 --> 00:10:59.660 align:middle line:84% So this is known as the Mixed Alkali Effect. 00:10:59.660 --> 00:11:04.980 align:middle line:84% So to illustrate this effect, what I'm showing on this plot 00:11:04.980 --> 00:11:07.260 align:middle line:84% here on the left-hand side, vertical axis 00:11:07.260 --> 00:11:09.540 align:middle line:84% is basically a logarithm viscosity 00:11:09.540 --> 00:11:13.240 align:middle line:84% of some silicate glasses mixed with either sodium oxide 00:11:13.240 --> 00:11:14.600 align:middle line:90% and potassium oxide. 00:11:14.600 --> 00:11:20.060 align:middle line:84% Horizontal axis, this is the molar fraction of sodium oxide. 00:11:20.060 --> 00:11:23.000 align:middle line:84% So you keep the total amount of alkaline ion constant, 00:11:23.000 --> 00:11:25.340 align:middle line:84% you are essentially changing the relative fraction, 00:11:25.340 --> 00:11:29.740 align:middle line:84% the relative concentration of sodium and potassium ions. 00:11:29.740 --> 00:11:32.020 align:middle line:84% Now, notice that this curve, they always 00:11:32.020 --> 00:11:35.420 align:middle line:84% have this kind of a concave shape. 00:11:35.420 --> 00:11:40.100 align:middle line:84% So the viscosity decreases by a couple of orders of magnitude 00:11:40.100 --> 00:11:44.220 align:middle line:84% if you go into intermediate composition. 00:11:44.220 --> 00:11:48.340 align:middle line:84% So basically says the glass becomes a lot more deformable 00:11:48.340 --> 00:11:50.080 align:middle line:84% if you mix two kinds of alkali ions, 00:11:50.080 --> 00:11:53.780 align:middle line:84% even if you keep the total concentration the same. 00:11:53.780 --> 00:11:56.700 align:middle line:84% I want to mention that this effect exists not only for just 00:11:56.700 --> 00:11:59.403 align:middle line:84% viscosity, it actually exists for many physical properties 00:11:59.403 --> 00:12:01.820 align:middle line:84% of glass materials, especially in terms of their transport 00:12:01.820 --> 00:12:02.360 align:middle line:90% properties. 00:12:02.360 --> 00:12:05.900 align:middle line:84% So only this middle plot here, I'm 00:12:05.900 --> 00:12:08.420 align:middle line:84% now plotting diffusion coefficient-- again, similarly 00:12:08.420 --> 00:12:11.820 align:middle line:84% as the composition of these two alkali ion atoms. 00:12:11.820 --> 00:12:14.820 align:middle line:84% And you see similar kind of a dip behavior there. 00:12:14.820 --> 00:12:17.700 align:middle line:84% You have the minimum diffusion at some intermediate composition 00:12:17.700 --> 00:12:19.020 align:middle line:90% here. 00:12:19.020 --> 00:12:22.360 align:middle line:84% So the origin of the mixed alkaline effect-- 00:12:22.360 --> 00:12:26.513 align:middle line:84% this is still an issue still of intensive investigation. 00:12:26.513 --> 00:12:28.180 align:middle line:84% People have come up with different kinds 00:12:28.180 --> 00:12:30.638 align:middle line:84% of explanations with respect to different specific physical 00:12:30.638 --> 00:12:31.820 align:middle line:90% effects. 00:12:31.820 --> 00:12:34.100 align:middle line:84% The most commonly assumed reason is 00:12:34.100 --> 00:12:37.220 align:middle line:84% that this comes from mutual blocking of transport 00:12:37.220 --> 00:12:38.580 align:middle line:90% pathways between ions. 00:12:38.580 --> 00:12:41.340 align:middle line:84% If you imagine, for example, you have a glass network that 00:12:41.340 --> 00:12:44.230 align:middle line:84% contains, say, only one kind of ion, let's say sodium, 00:12:44.230 --> 00:12:45.980 align:middle line:84% all the sodium ions, they have essentially 00:12:45.980 --> 00:12:48.980 align:middle line:84% their respective size that they can comfortably be sitting in. 00:12:48.980 --> 00:12:51.540 align:middle line:84% And when any kind of transport phenomena like diffusion 00:12:51.540 --> 00:12:55.540 align:middle line:84% happens, what is required is that the sodium ion, 00:12:55.540 --> 00:12:58.680 align:middle line:84% they have to hop from one sodium side to another sodium side. 00:12:58.680 --> 00:13:03.100 align:middle line:84% That's how you perform ion conduction or perform diffusion. 00:13:03.100 --> 00:13:04.700 align:middle line:84% Now, if you only have sodium, then you 00:13:04.700 --> 00:13:06.783 align:middle line:84% can imagine that all the sides, more or less, they 00:13:06.783 --> 00:13:08.940 align:middle line:84% have similar energy, so it's quite easy for them 00:13:08.940 --> 00:13:11.260 align:middle line:84% to move around without experiencing a large energy 00:13:11.260 --> 00:13:13.340 align:middle line:90% barrier. 00:13:13.340 --> 00:13:17.060 align:middle line:84% If you go to now mix alkalines, you 00:13:17.060 --> 00:13:21.460 align:middle line:84% get two kind of sides for this kind of ions. 00:13:21.460 --> 00:13:24.387 align:middle line:84% And this creates large energy differences 00:13:24.387 --> 00:13:26.720 align:middle line:84% when they are hopping between the different sides there. 00:13:26.720 --> 00:13:29.900 align:middle line:84% For example, if you're trying to squeeze especially potassium, 00:13:29.900 --> 00:13:32.215 align:middle line:84% a larger ion, into smaller ions like sodium sides, 00:13:32.215 --> 00:13:33.840 align:middle line:84% then there's a lot of steric hindrance. 00:13:33.840 --> 00:13:35.280 align:middle line:84% And therefore, it increases the energy 00:13:35.280 --> 00:13:36.900 align:middle line:84% you need to actually move these ions. 00:13:36.900 --> 00:13:40.020 align:middle line:84% And in the end, that's why it actually inhibits this transport 00:13:40.020 --> 00:13:40.740 align:middle line:90% behavior. 00:13:40.740 --> 00:13:43.170 align:middle line:84% And that's the explanation that people 00:13:43.170 --> 00:13:47.950 align:middle line:84% are giving for this kind of mixed alkaline effect. 00:13:47.950 --> 00:13:51.970 align:middle line:84% So I just want to mention that this mixed alkali effect, this 00:13:51.970 --> 00:13:54.850 align:middle line:84% is something that people have actually discovered long ago. 00:13:54.850 --> 00:14:00.050 align:middle line:84% So this is accounts of some historic records that 00:14:00.050 --> 00:14:03.250 align:middle line:84% mention that, in the early days, when people were actually making 00:14:03.250 --> 00:14:05.250 align:middle line:90% thermometers out of glass-- 00:14:05.250 --> 00:14:07.490 align:middle line:84% so some early thermometers, they put 00:14:07.490 --> 00:14:09.548 align:middle line:84% something like mercury into a glass tube, 00:14:09.548 --> 00:14:11.090 align:middle line:84% and looking at the thermal expansion, 00:14:11.090 --> 00:14:12.910 align:middle line:84% and use that to determine temperature. 00:14:12.910 --> 00:14:17.490 align:middle line:84% Now, what they have noticed here is that you have freshly 00:14:17.490 --> 00:14:19.010 align:middle line:90% made glass. 00:14:19.010 --> 00:14:21.250 align:middle line:84% You directly put mercury in there. 00:14:21.250 --> 00:14:26.570 align:middle line:84% You then put it into, for example, ice water, 00:14:26.570 --> 00:14:28.410 align:middle line:84% it would show 0 degrees C. But then 00:14:28.410 --> 00:14:30.850 align:middle line:84% if you put it into boiling water and then put it back 00:14:30.850 --> 00:14:33.690 align:middle line:84% into ice water, instead of showing 0 degrees C, 00:14:33.690 --> 00:14:35.450 align:middle line:84% it would show actually negative 5 degrees 00:14:35.450 --> 00:14:38.530 align:middle line:84% C, because when you actually put the glass in boiling water, 00:14:38.530 --> 00:14:42.550 align:middle line:84% because of high temperature and then it decreases the viscosity, 00:14:42.550 --> 00:14:44.610 align:middle line:84% you start to get shape deformation and relaxation 00:14:44.610 --> 00:14:45.750 align:middle line:90% of internal stress. 00:14:45.750 --> 00:14:49.050 align:middle line:84% As a result, this leads to macroscopic deformation 00:14:49.050 --> 00:14:52.090 align:middle line:84% that then compromises the accuracy of this thermometer. 00:14:52.090 --> 00:14:55.450 align:middle line:84% So they have noticed there that if you actually 00:14:55.450 --> 00:15:00.610 align:middle line:84% store these glasses at just an ambient condition 00:15:00.610 --> 00:15:04.110 align:middle line:84% for several months before you make it into a thermometer, 00:15:04.110 --> 00:15:06.090 align:middle line:90% then this phenomena goes away. 00:15:06.090 --> 00:15:08.250 align:middle line:84% Now, that's actually easy to explain, 00:15:08.250 --> 00:15:11.970 align:middle line:84% because now we understand this is coming from relaxation. 00:15:11.970 --> 00:15:14.690 align:middle line:84% So if you allow all the internal stress, 00:15:14.690 --> 00:15:17.410 align:middle line:84% shape deformation take place in over the several months 00:15:17.410 --> 00:15:20.890 align:middle line:84% of period, then you no longer have this effect. 00:15:20.890 --> 00:15:22.810 align:middle line:84% However, what they have also noticed here 00:15:22.810 --> 00:15:26.290 align:middle line:84% is that if you heat it up again and cool it down, 00:15:26.290 --> 00:15:28.330 align:middle line:84% then that phenomenon comes in again. 00:15:28.330 --> 00:15:30.372 align:middle line:84% You are essentially going through the same cycle. 00:15:30.372 --> 00:15:32.890 align:middle line:84% You heat it up, back to like a super cool liquid, quenches 00:15:32.890 --> 00:15:36.092 align:middle line:84% back down, it erases any memory of the relaxation. 00:15:36.092 --> 00:15:37.550 align:middle line:84% So you have the same problem again. 00:15:37.550 --> 00:15:39.210 align:middle line:90% Relaxation comes in again. 00:15:39.210 --> 00:15:42.890 align:middle line:84% And finally, what they have noticed 00:15:42.890 --> 00:15:44.668 align:middle line:84% there is that this relaxation effect 00:15:44.668 --> 00:15:46.210 align:middle line:84% could be diminished by a factor of 10 00:15:46.210 --> 00:15:48.710 align:middle line:84% if only one type of alkaline ion is used 00:15:48.710 --> 00:15:50.610 align:middle line:90% rather than using mixed ions. 00:15:50.610 --> 00:15:52.890 align:middle line:84% So that's basically the first account 00:15:52.890 --> 00:15:55.432 align:middle line:84% for this kind of mixed alkaline effect. 00:15:55.432 --> 00:15:56.890 align:middle line:84% You're mixing two kind of ions, you 00:15:56.890 --> 00:15:59.210 align:middle line:84% decrease the viscosity and therefore 00:15:59.210 --> 00:16:03.010 align:middle line:90% the working temperatures. 00:16:03.010 --> 00:16:06.170 align:middle line:84% So far, we have been discussing about the temperature 00:16:06.170 --> 00:16:09.890 align:middle line:84% dependence of viscosity in amorphous materials. 00:16:09.890 --> 00:16:12.612 align:middle line:84% The next topic I want to mention here is that viscosity, 00:16:12.612 --> 00:16:14.070 align:middle line:84% it not only depends on temperature, 00:16:14.070 --> 00:16:16.370 align:middle line:90% it also depends on shear rate. 00:16:16.370 --> 00:16:17.210 align:middle line:90% OK. 00:16:17.210 --> 00:16:20.730 align:middle line:84% And this is quite common in a lot of fluids, including 00:16:20.730 --> 00:16:23.520 align:middle line:90% glass-forming liquids. 00:16:23.520 --> 00:16:25.770 align:middle line:84% Now, if you look at the equation we have been starting 00:16:25.770 --> 00:16:27.950 align:middle line:84% to talking about here in the very first slide, 00:16:27.950 --> 00:16:32.130 align:middle line:84% we said that if you assume a liquid has a Newtonian behavior, 00:16:32.130 --> 00:16:34.907 align:middle line:90% then its viscosity is constant. 00:16:34.907 --> 00:16:36.490 align:middle line:84% It does not depend on the strain rate, 00:16:36.490 --> 00:16:38.970 align:middle line:84% and therefore the shear stress should be proportional 00:16:38.970 --> 00:16:41.210 align:middle line:90% to the shear strain rate. 00:16:41.210 --> 00:16:45.250 align:middle line:84% In reality, you can have different kind 00:16:45.250 --> 00:16:48.870 align:middle line:84% of a dependence of the viscosity on the shear rate. 00:16:48.870 --> 00:16:51.250 align:middle line:84% So what I'm plotting on this plot here 00:16:51.250 --> 00:16:55.090 align:middle line:84% is some of this kind of typical fluids, when they 00:16:55.090 --> 00:16:56.650 align:middle line:90% exhibit different behaviors. 00:16:56.650 --> 00:16:59.090 align:middle line:84% So the Newtonian fluid, this would 00:16:59.090 --> 00:17:03.970 align:middle line:84% be a straight line here for the stress and strain rate curve. 00:17:03.970 --> 00:17:06.973 align:middle line:84% And basically, it says that the slope of this line 00:17:06.973 --> 00:17:08.890 align:middle line:84% will give you the viscosity, and it's constant 00:17:08.890 --> 00:17:10.369 align:middle line:90% regardless of strain rate. 00:17:10.369 --> 00:17:14.329 align:middle line:90% You can have shear thinning. 00:17:14.329 --> 00:17:17.977 align:middle line:84% As you increase the shear rate, the liquid becomes thinner. 00:17:17.977 --> 00:17:20.310 align:middle line:84% It becomes easier to deform, it becomes lower viscosity. 00:17:20.310 --> 00:17:21.630 align:middle line:90% It's more flowable. 00:17:21.630 --> 00:17:23.390 align:middle line:90% Or it can be shear thickening. 00:17:23.390 --> 00:17:26.630 align:middle line:84% As you increase strain rate, it actually becomes thicker. 00:17:26.630 --> 00:17:27.970 align:middle line:90% It becomes more viscous. 00:17:27.970 --> 00:17:31.730 align:middle line:84% Now, you can also have a so-called Bingham plastic. 00:17:31.730 --> 00:17:34.010 align:middle line:84% Bingham plastic has this interesting behavior 00:17:34.010 --> 00:17:37.710 align:middle line:84% that if your stress is below a certain threshold, 00:17:37.710 --> 00:17:39.810 align:middle line:90% it behaves more like a solid. 00:17:39.810 --> 00:17:42.490 align:middle line:84% It does not exhibit any kind of flow behavior. 00:17:42.490 --> 00:17:44.150 align:middle line:84% Now, once you exceed the threshold, 00:17:44.150 --> 00:17:47.850 align:middle line:84% now it starts to flow, now it behaves like a liquid. 00:17:47.850 --> 00:17:51.430 align:middle line:84% In fact, the common example of Bingham plastic is toothpaste. 00:17:51.430 --> 00:17:54.168 align:middle line:84% A lot of toothpaste is actually Bingham fluid plastic. 00:17:54.168 --> 00:17:55.710 align:middle line:84% If you think about toothpaste, right, 00:17:55.710 --> 00:17:59.890 align:middle line:84% if you just leave it there, it will hold its shape. 00:17:59.890 --> 00:18:02.390 align:middle line:84% But once you start to brush, of course, it starts to deform. 00:18:02.390 --> 00:18:04.265 align:middle line:84% That's when you actually apply enough stress, 00:18:04.265 --> 00:18:08.430 align:middle line:84% exceed the threshold to induce the viscous flow. 00:18:08.430 --> 00:18:08.930 align:middle line:90% OK. 00:18:08.930 --> 00:18:11.650 align:middle line:90% 00:18:11.650 --> 00:18:13.408 align:middle line:84% For amorphous materials, depending 00:18:13.408 --> 00:18:15.450 align:middle line:84% on what kind of material you're looking at there, 00:18:15.450 --> 00:18:20.623 align:middle line:84% they can either exhibit stress or shear thickening. 00:18:20.623 --> 00:18:22.290 align:middle line:84% And I'll give you some specific examples 00:18:22.290 --> 00:18:26.405 align:middle line:84% about this different kind of fluids there. 00:18:26.405 --> 00:18:28.530 align:middle line:84% And then on this next slide, on the left-hand side, 00:18:28.530 --> 00:18:30.610 align:middle line:84% I'm basically now, in this case, just plotting the viscosity 00:18:30.610 --> 00:18:32.105 align:middle line:90% as a function of shear rate. 00:18:32.105 --> 00:18:33.230 align:middle line:90% Same idea as the last plot. 00:18:33.230 --> 00:18:35.813 align:middle line:84% We are just now looking at the slope from the last plot there. 00:18:35.813 --> 00:18:36.650 align:middle line:90% OK. 00:18:36.650 --> 00:18:41.250 align:middle line:84% Microscopically, what's the mechanism 00:18:41.250 --> 00:18:43.650 align:middle line:84% for this different kind of fluids? 00:18:43.650 --> 00:18:46.410 align:middle line:84% Viscosity, as we have mentioned before, 00:18:46.410 --> 00:18:48.930 align:middle line:90% is internal friction in liquids. 00:18:48.930 --> 00:18:52.090 align:middle line:84% Viscous flow is when one part of liquid, some of the molecules, 00:18:52.090 --> 00:18:54.010 align:middle line:90% has to move past the others. 00:18:54.010 --> 00:18:56.158 align:middle line:84% And viscosity is the resistance of the material 00:18:56.158 --> 00:18:58.450 align:middle line:84% to this kind of relative motion between different parts 00:18:58.450 --> 00:18:59.730 align:middle line:90% of molecules. 00:18:59.730 --> 00:19:04.490 align:middle line:84% So for shear thickening, what happens 00:19:04.490 --> 00:19:07.010 align:middle line:84% there is that, as you increase the strain rate, 00:19:07.010 --> 00:19:09.610 align:middle line:84% the molecules start to self-assemble together 00:19:09.610 --> 00:19:11.810 align:middle line:90% to form larger clusters. 00:19:11.810 --> 00:19:13.730 align:middle line:84% And with larger clusters, it becomes 00:19:13.730 --> 00:19:15.590 align:middle line:84% more difficult to actually deform it. 00:19:15.590 --> 00:19:17.650 align:middle line:84% And as a result, you see apparent increase 00:19:17.650 --> 00:19:20.090 align:middle line:90% of the viscosity. 00:19:20.090 --> 00:19:23.617 align:middle line:84% So this is a phenomenon called hydroclustering. 00:19:23.617 --> 00:19:24.950 align:middle line:90% It's basically illustrated here. 00:19:24.950 --> 00:19:27.770 align:middle line:84% When there is no shear stress or the molecular fragments 00:19:27.770 --> 00:19:29.630 align:middle line:90% stay separated. 00:19:29.630 --> 00:19:31.830 align:middle line:84% But once you start to apply large shear rate, 00:19:31.830 --> 00:19:34.920 align:middle line:84% then they start to organize, self-assemble together to form 00:19:34.920 --> 00:19:38.720 align:middle line:84% larger structures, which impedes viscous flow. 00:19:38.720 --> 00:19:42.320 align:middle line:84% So lots of liquids actually exhibit a shear thickening 00:19:42.320 --> 00:19:44.280 align:middle line:90% behavior. 00:19:44.280 --> 00:19:47.160 align:middle line:84% I'm showing you this little video here. 00:19:47.160 --> 00:19:53.440 align:middle line:84% It basically shows someone that's running on liquid. 00:19:53.440 --> 00:19:56.285 align:middle line:84% This liquid, this is called oobleck. 00:19:56.285 --> 00:19:57.660 align:middle line:84% You can actually make it at home. 00:19:57.660 --> 00:19:58.420 align:middle line:90% It's quite straightforward. 00:19:58.420 --> 00:19:59.940 align:middle line:90% It's basically starch and water. 00:19:59.940 --> 00:20:01.880 align:middle line:84% You mix it with about one-to-two ratio, 00:20:01.880 --> 00:20:03.585 align:middle line:84% and then you get liquid like this. 00:20:03.585 --> 00:20:05.960 align:middle line:84% It is quite remarkable because if you do it, what happens 00:20:05.960 --> 00:20:09.360 align:middle line:84% is that if you just try to use a spoon or something to screw it 00:20:09.360 --> 00:20:11.520 align:middle line:90% up, it behaves just like liquid. 00:20:11.520 --> 00:20:14.140 align:middle line:84% But if you try to change its shape, you put it in your hand, 00:20:14.140 --> 00:20:15.960 align:middle line:84% try to mold it into some shape, as long 00:20:15.960 --> 00:20:19.520 align:middle line:84% as you do it quick enough, it behaves more like a solid. 00:20:19.520 --> 00:20:20.020 align:middle line:90% OK. 00:20:20.020 --> 00:20:22.602 align:middle line:84% So that's one good example of this shear thickening behavior. 00:20:22.602 --> 00:20:24.560 align:middle line:84% And that's why you see that people can actually 00:20:24.560 --> 00:20:25.980 align:middle line:90% run on this kind of liquid. 00:20:25.980 --> 00:20:28.320 align:middle line:84% As long as you do it fast enough, 00:20:28.320 --> 00:20:30.930 align:middle line:84% you are not risking sinking into the liquid. 00:20:30.930 --> 00:20:32.680 align:middle line:84% Actually, you can find some YouTube videos 00:20:32.680 --> 00:20:34.860 align:middle line:84% where people actually play soccer on this oobleck, 00:20:34.860 --> 00:20:37.440 align:middle line:84% like a big swimming pool filled with oobleck. 00:20:37.440 --> 00:20:39.460 align:middle line:84% But you have to keep it running all the time. 00:20:39.460 --> 00:20:45.240 align:middle line:84% As soon as you stop, pssh, you sink into liquid. 00:20:45.240 --> 00:20:48.960 align:middle line:90% Some other examples. 00:20:48.960 --> 00:20:51.260 align:middle line:90% Any of you know Silly Putty? 00:20:51.260 --> 00:20:51.760 align:middle line:90% Oh, yeah. 00:20:51.760 --> 00:20:53.260 align:middle line:90% Silly Putty. 00:20:53.260 --> 00:20:54.960 align:middle line:90% This is similar. 00:20:54.960 --> 00:20:57.623 align:middle line:84% Silly Putty, you can shape, mold into a ball. 00:20:57.623 --> 00:21:00.040 align:middle line:84% And if you throw it on the floor, it actually bounce back. 00:21:00.040 --> 00:21:02.060 align:middle line:84% It's basically like a rock, a solid. 00:21:02.060 --> 00:21:04.333 align:middle line:84% But if you try to let it flow a little bit, 00:21:04.333 --> 00:21:06.000 align:middle line:84% you put it into a container, it actually 00:21:06.000 --> 00:21:07.760 align:middle line:84% can flow and conform to the shape. 00:21:07.760 --> 00:21:11.580 align:middle line:84% So as long as you have a low stress, 00:21:11.580 --> 00:21:14.240 align:middle line:84% then its viscosity decreases and then you allow it to flow. 00:21:14.240 --> 00:21:17.640 align:middle line:84% So these are the examples of this kind of fluids there. 00:21:17.640 --> 00:21:19.400 align:middle line:90% Shear thickening. 00:21:19.400 --> 00:21:20.580 align:middle line:90% Shear thinning. 00:21:20.580 --> 00:21:23.560 align:middle line:90% 00:21:23.560 --> 00:21:27.800 align:middle line:84% The common example of shear thinning is paint-- 00:21:27.800 --> 00:21:28.700 align:middle line:90% house paint. 00:21:28.700 --> 00:21:32.200 align:middle line:90% 00:21:32.200 --> 00:21:34.720 align:middle line:84% So shear thinning is quite desirable for paint 00:21:34.720 --> 00:21:36.602 align:middle line:84% because when you're trying to brush it, 00:21:36.602 --> 00:21:38.060 align:middle line:84% you want to make sure it's a fluid, 00:21:38.060 --> 00:21:40.160 align:middle line:84% you can actually apply it uniformly on the wall. 00:21:40.160 --> 00:21:41.640 align:middle line:90% So you need low viscosity. 00:21:41.640 --> 00:21:44.260 align:middle line:84% But once you put it on the wall, you want it to stick there. 00:21:44.260 --> 00:21:46.360 align:middle line:84% You don't want it to continue to flow. 00:21:46.360 --> 00:21:48.500 align:middle line:84% So that's why people actually engineer it 00:21:48.500 --> 00:21:50.880 align:middle line:84% so it has shear thinning characteristics such 00:21:50.880 --> 00:21:53.720 align:middle line:84% that when you stop applying any stress, 00:21:53.720 --> 00:21:55.340 align:middle line:84% its viscosity actually increases. 00:21:55.340 --> 00:21:56.240 align:middle line:84% And that's why you can actually have 00:21:56.240 --> 00:21:58.240 align:middle line:84% a uniform coating on the wall without continuing 00:21:58.240 --> 00:22:00.100 align:middle line:90% to flow before it dries. 00:22:00.100 --> 00:22:02.600 align:middle line:84% Another more state-of-the-art example where people are using 00:22:02.600 --> 00:22:05.240 align:middle line:84% this kind of shear thinning characteristic to some benefits 00:22:05.240 --> 00:22:08.680 align:middle line:84% here is when people are doing 3D printing. 00:22:08.680 --> 00:22:13.440 align:middle line:84% So 3D printing involves-- you have some polymer. 00:22:13.440 --> 00:22:16.280 align:middle line:84% You start to squeeze it out of a nozzle. 00:22:16.280 --> 00:22:19.460 align:middle line:84% And as you translate this nozzle in 3D space, 00:22:19.460 --> 00:22:23.760 align:middle line:84% you then leave behind a trace of this polymer in 3D space. 00:22:23.760 --> 00:22:26.040 align:middle line:84% Now, shear thinning is, again, advantageous 00:22:26.040 --> 00:22:28.960 align:middle line:84% here, because when you're trying to squeeze polymer out 00:22:28.960 --> 00:22:32.480 align:middle line:84% of a nozzle, this is basically a viscous flow process. 00:22:32.480 --> 00:22:34.340 align:middle line:84% If you have a very high viscosity, 00:22:34.340 --> 00:22:37.160 align:middle line:84% it becomes very difficult just to force the polymer out 00:22:37.160 --> 00:22:37.960 align:middle line:90% of the nozzle. 00:22:37.960 --> 00:22:40.360 align:middle line:84% And again, once you are printed or you 00:22:40.360 --> 00:22:42.360 align:middle line:84% have finished your printing, you want your shape 00:22:42.360 --> 00:22:43.520 align:middle line:90% to actually stay static. 00:22:43.520 --> 00:22:45.812 align:middle line:84% You don't want it to continue to flow to deform things. 00:22:45.812 --> 00:22:48.520 align:middle line:84% So that's why, if you have shear thinning fluids, then 00:22:48.520 --> 00:22:51.020 align:middle line:84% at the nozzle, this is where you have very large shear rate, 00:22:51.020 --> 00:22:52.620 align:middle line:84% you have a decrease of viscosity. 00:22:52.620 --> 00:22:54.620 align:middle line:84% But once it comes out, you relax all the stress, 00:22:54.620 --> 00:22:57.600 align:middle line:84% you release all the stress, then you can have high viscosity 00:22:57.600 --> 00:23:00.540 align:middle line:90% to hold the shape. 00:23:00.540 --> 00:23:04.520 align:middle line:90% So now coming back to glass. 00:23:04.520 --> 00:23:07.680 align:middle line:84% So what I'm plotting here, this is actually for soda-lime glass. 00:23:07.680 --> 00:23:10.440 align:middle line:84% It plots how the viscosity actually 00:23:10.440 --> 00:23:13.480 align:middle line:84% changes as a function of the strain rate. 00:23:13.480 --> 00:23:15.440 align:middle line:84% And according to this plot, you can 00:23:15.440 --> 00:23:18.560 align:middle line:84% see that soda-lime glass actually exhibits a fairly clear 00:23:18.560 --> 00:23:21.840 align:middle line:90% shear thinning behavior. 00:23:21.840 --> 00:23:23.840 align:middle line:84% So viscosity of soda-lime glasses 00:23:23.840 --> 00:23:26.220 align:middle line:84% decreases as you increase the strain rate. 00:23:26.220 --> 00:23:29.480 align:middle line:90% 00:23:29.480 --> 00:23:32.000 align:middle line:90% Now, why is this important? 00:23:32.000 --> 00:23:34.440 align:middle line:84% When it comes to glass processing, 00:23:34.440 --> 00:23:37.680 align:middle line:84% especially in glass processes, where, in the same process, 00:23:37.680 --> 00:23:40.720 align:middle line:84% you have large differences of shear rate, 00:23:40.720 --> 00:23:44.160 align:middle line:84% then this is something that has to be taken into account. 00:23:44.160 --> 00:23:47.920 align:middle line:84% One example there would be an optical fiber join. 00:23:47.920 --> 00:23:50.680 align:middle line:84% So we will be talking about optical fiber 00:23:50.680 --> 00:23:52.620 align:middle line:84% joining processes later on in the class. 00:23:52.620 --> 00:23:56.200 align:middle line:84% But essentially, what you do is you have a macroscopic preform, 00:23:56.200 --> 00:23:58.040 align:middle line:84% which is about a couple of centimeters 00:23:58.040 --> 00:23:59.740 align:middle line:90% in diameter, a cylinder. 00:23:59.740 --> 00:24:01.760 align:middle line:84% You then put it into a furnace, so 00:24:01.760 --> 00:24:03.700 align:middle line:84% that you start to induce viscous flow, 00:24:03.700 --> 00:24:07.160 align:middle line:84% and you apply tensile stress on one end, which 00:24:07.160 --> 00:24:13.780 align:middle line:84% then deforms this cylinder into a very thin strand of the fiber. 00:24:13.780 --> 00:24:15.880 align:middle line:84% Now, if you look at the process here, 00:24:15.880 --> 00:24:20.280 align:middle line:84% the deformation rate, or shear rate, is very non-uniform. 00:24:20.280 --> 00:24:22.760 align:middle line:84% At this part, at this macroscopic preform 00:24:22.760 --> 00:24:26.250 align:middle line:84% here, the shear rate is actually very, very small. 00:24:26.250 --> 00:24:27.250 align:middle line:90% It barely deforms. 00:24:27.250 --> 00:24:29.590 align:middle line:84% But the shear rate scales, actually, 00:24:29.590 --> 00:24:32.570 align:middle line:84% inversely with the diameter of the glass. 00:24:32.570 --> 00:24:35.470 align:middle line:84% So when you come to the fiber part here, 00:24:35.470 --> 00:24:37.910 align:middle line:84% you actually have a very large shear rate 00:24:37.910 --> 00:24:40.190 align:middle line:90% during the formation process. 00:24:40.190 --> 00:24:41.710 align:middle line:84% So when you're actually developing 00:24:41.710 --> 00:24:46.510 align:middle line:84% any kind of a modeling process for this fiber drawing 00:24:46.510 --> 00:24:49.950 align:middle line:84% technique, you need to account for the viscosity change. 00:24:49.950 --> 00:24:52.350 align:middle line:84% The actual viscosity-- apparent viscosity of the glass 00:24:52.350 --> 00:24:55.450 align:middle line:84% is much lower here compared to up here, 00:24:55.450 --> 00:24:58.710 align:middle line:84% even if you are at the same temperature. 00:24:58.710 --> 00:25:02.742 align:middle line:84% Otherwise, you may risk breaking the fiber 00:25:02.742 --> 00:25:04.950 align:middle line:84% or having non-uniformity there, if you don't properly 00:25:04.950 --> 00:25:07.070 align:middle line:84% account for this kind of shear rate 00:25:07.070 --> 00:25:08.450 align:middle line:90% dependence of the viscosity. 00:25:08.450 --> 00:25:13.310 align:middle line:90% 00:25:13.310 --> 00:25:18.292 align:middle line:84% So before I talk about how to measure viscosity, 00:25:18.292 --> 00:25:19.750 align:middle line:84% I just want to show you this slide. 00:25:19.750 --> 00:25:21.230 align:middle line:84% When I was looking for literature 00:25:21.230 --> 00:25:26.470 align:middle line:84% on non-Newtonian fluids, people, obviously, have identified cats 00:25:26.470 --> 00:25:28.590 align:middle line:90% as non-Newtonian fluids. 00:25:28.590 --> 00:25:30.030 align:middle line:90% They actually published a paper. 00:25:30.030 --> 00:25:33.630 align:middle line:84% They tried to fit all kinds of fluid dynamic equations 00:25:33.630 --> 00:25:35.560 align:middle line:84% and used that to describe cat behavior. 00:25:35.560 --> 00:25:36.810 align:middle line:90% And in the illustration here-- 00:25:36.810 --> 00:25:38.435 align:middle line:84% I don't know if you can see it clearly, 00:25:38.435 --> 00:25:40.590 align:middle line:84% but it shows a few examples why they consider cat 00:25:40.590 --> 00:25:43.710 align:middle line:84% as being a fluid instead of a solid. 00:25:43.710 --> 00:25:45.870 align:middle line:84% Obviously, they can conform into different shapes. 00:25:45.870 --> 00:25:48.132 align:middle line:84% They can handle uneven substrates. 00:25:48.132 --> 00:25:49.590 align:middle line:84% You can see there they can actually 00:25:49.590 --> 00:25:52.550 align:middle line:84% have non-wetting behavior on water surface. 00:25:52.550 --> 00:25:54.690 align:middle line:84% And this one, they can glide on a smooth surface. 00:25:54.690 --> 00:25:56.690 align:middle line:84% They can also hang onto vertical walls. 00:25:56.690 --> 00:25:59.990 align:middle line:84% So all those behaviors are unique to liquids, 00:25:59.990 --> 00:26:01.050 align:middle line:90% not to solids. 00:26:01.050 --> 00:26:03.695 align:middle line:84% So that's why they conclude that cat is actually a liquid. 00:26:03.695 --> 00:26:05.070 align:middle line:84% And they have some equations that 00:26:05.070 --> 00:26:07.750 align:middle line:84% consider the relations to actually describe cats. 00:26:07.750 --> 00:26:10.610 align:middle line:84% So quite an entertaining paper if you ever want to read it. 00:26:10.610 --> 00:26:13.970 align:middle line:84% And this is also won the Ig Nobel Prize, this research. 00:26:13.970 --> 00:26:18.350 align:middle line:84% AUDIENCE: So they're like the author affiliations? 00:26:18.350 --> 00:26:19.310 align:middle line:90% PROFESSOR: Oh, yeah. 00:26:19.310 --> 00:26:23.890 align:middle line:84% AUDIENCE: [INAUDIBLE] superior radiologist? 00:26:23.890 --> 00:26:27.170 align:middle line:90% 00:26:27.170 --> 00:26:29.670 align:middle line:84% PROFESSOR: I was hoping they should include some of the cats 00:26:29.670 --> 00:26:31.670 align:middle line:90% as coauthors. 00:26:31.670 --> 00:26:33.520 align:middle line:84% But they are important experimental subjects 00:26:33.520 --> 00:26:34.770 align:middle line:90% that contributed to the study. 00:26:34.770 --> 00:26:35.530 align:middle line:90% But whatever. 00:26:35.530 --> 00:26:38.870 align:middle line:90% 00:26:38.870 --> 00:26:40.750 align:middle line:90% Anyway. 00:26:40.750 --> 00:26:41.250 align:middle line:90% All right. 00:26:41.250 --> 00:26:44.550 align:middle line:84% So the last point I want to mention here about viscosity 00:26:44.550 --> 00:26:47.490 align:middle line:84% is how do people characterize viscosity in glass melts. 00:26:47.490 --> 00:26:50.390 align:middle line:84% Now, viscosity is one of the phenomena that can span 00:26:50.390 --> 00:26:52.150 align:middle line:90% many, many orders of magnitude. 00:26:52.150 --> 00:26:53.870 align:middle line:84% So it's not surprising at all that you 00:26:53.870 --> 00:26:56.037 align:middle line:84% have to use different techniques to actually measure 00:26:56.037 --> 00:26:57.430 align:middle line:90% viscosity in different ranges. 00:26:57.430 --> 00:26:59.990 align:middle line:84% So if you're trying to measure viscosity 00:26:59.990 --> 00:27:02.430 align:middle line:84% in the low-viscosity regime, it behaves more 00:27:02.430 --> 00:27:04.590 align:middle line:90% like liquid, flowable liquid. 00:27:04.590 --> 00:27:06.390 align:middle line:84% So what you're typically supposed to do 00:27:06.390 --> 00:27:08.670 align:middle line:84% is use this kind of rotating cylinder approach. 00:27:08.670 --> 00:27:11.670 align:middle line:84% You essentially put the liquid in between the rotating cylinder 00:27:11.670 --> 00:27:13.110 align:middle line:90% and the container. 00:27:13.110 --> 00:27:15.190 align:middle line:84% And you can then measure what torque 00:27:15.190 --> 00:27:18.350 align:middle line:84% you need to apply depending on the spin rate. 00:27:18.350 --> 00:27:20.830 align:middle line:84% So from that, you can actually infer 00:27:20.830 --> 00:27:23.910 align:middle line:84% what is the viscosity, the friction the liquid exerts 00:27:23.910 --> 00:27:25.210 align:middle line:90% on the spinning cylinder. 00:27:25.210 --> 00:27:28.530 align:middle line:84% Now, if you go to a higher viscosity, 00:27:28.530 --> 00:27:31.130 align:middle line:84% this is somewhere around the working range. 00:27:31.130 --> 00:27:34.190 align:middle line:90% So chewing gum, like glasses. 00:27:34.190 --> 00:27:36.390 align:middle line:84% Instead of using this kind of rotating cylinder, 00:27:36.390 --> 00:27:38.870 align:middle line:84% you actually use a parallel plate approach. 00:27:38.870 --> 00:27:42.550 align:middle line:84% So you put some glass materials between two parallel plates. 00:27:42.550 --> 00:27:44.590 align:middle line:84% And then you start to rotate one of the plates 00:27:44.590 --> 00:27:46.030 align:middle line:90% with respect to another. 00:27:46.030 --> 00:27:49.430 align:middle line:84% And similarly, you measure what is the torque 00:27:49.430 --> 00:27:54.590 align:middle line:84% you need to apply as a function of the rotational speed. 00:27:54.590 --> 00:27:57.710 align:middle line:84% Now, this only applies to this relatively high viscosity range, 00:27:57.710 --> 00:28:02.350 align:middle line:84% because if the glass melt flows like a liquid, 00:28:02.350 --> 00:28:04.110 align:middle line:84% it's going to leak out from the edges, 00:28:04.110 --> 00:28:05.690 align:middle line:90% so you cannot hold the shape. 00:28:05.690 --> 00:28:11.230 align:middle line:84% So that's why this applies only to intermediate viscosity range. 00:28:11.230 --> 00:28:13.230 align:middle line:84% Now, if you go to even higher viscosity, 00:28:13.230 --> 00:28:16.602 align:middle line:84% like a round glass transition temperature, 00:28:16.602 --> 00:28:18.810 align:middle line:84% the glass will behave more like a solid in this case. 00:28:18.810 --> 00:28:21.550 align:middle line:84% The deformation actually gets pretty small. 00:28:21.550 --> 00:28:24.330 align:middle line:84% So to measure the viscosity at this high viscosity range, 00:28:24.330 --> 00:28:27.710 align:middle line:84% you use techniques that you borrow from solid mechanics, 00:28:27.710 --> 00:28:28.550 align:middle line:90% like beam bending. 00:28:28.550 --> 00:28:30.390 align:middle line:84% This is like three-point beam bending. 00:28:30.390 --> 00:28:33.430 align:middle line:84% But the difference there, that in a conventional three-point 00:28:33.430 --> 00:28:36.030 align:middle line:84% beam bending, where we're trying to measure elastic material, 00:28:36.030 --> 00:28:37.870 align:middle line:84% you are trying to measure the force 00:28:37.870 --> 00:28:41.790 align:middle line:84% as a function of deformation, of displacement. 00:28:41.790 --> 00:28:42.630 align:middle line:90% That's what you do. 00:28:42.630 --> 00:28:44.630 align:middle line:84% That's how you infer the elastic constants. 00:28:44.630 --> 00:28:46.150 align:middle line:84% But in this case, if you're trying 00:28:46.150 --> 00:28:48.750 align:middle line:84% to measure viscosity, what we're trying to measure 00:28:48.750 --> 00:28:54.110 align:middle line:84% is the force as a function of deformation rate. 00:28:54.110 --> 00:28:56.110 align:middle line:84% It's not the absolute deformation that matters, 00:28:56.110 --> 00:28:58.590 align:middle line:90% it's how fast the beam sets. 00:28:58.590 --> 00:29:04.730 align:middle line:84% It's the movement speed is what really matters there. 00:29:04.730 --> 00:29:06.830 align:middle line:84% So this kind of a beam bending approach 00:29:06.830 --> 00:29:09.810 align:middle line:84% allows you to measure viscosity up to about 10 to the 13. 00:29:09.810 --> 00:29:13.412 align:middle line:84% So somewhere around, like, straining point. 00:29:13.412 --> 00:29:14.870 align:middle line:84% What if you want to study something 00:29:14.870 --> 00:29:19.230 align:middle line:90% with even higher viscosity? 00:29:19.230 --> 00:29:22.110 align:middle line:84% You may feel like that's not important, but turns out 00:29:22.110 --> 00:29:23.830 align:middle line:84% it can be quite relevant if you are 00:29:23.830 --> 00:29:26.790 align:middle line:84% trying to develop precision glass instruments, 00:29:26.790 --> 00:29:28.473 align:middle line:90% like big telescope mirrors. 00:29:28.473 --> 00:29:29.890 align:middle line:84% So a lot of big telescope mirrors, 00:29:29.890 --> 00:29:32.510 align:middle line:84% they obviously are quite heavy and they 00:29:32.510 --> 00:29:34.450 align:middle line:84% need to achieve extremely high precision. 00:29:34.450 --> 00:29:37.350 align:middle line:84% The surface has to have a shape deviation that's 00:29:37.350 --> 00:29:41.310 align:middle line:84% less than a fraction of the wavelength of the light. 00:29:41.310 --> 00:29:43.870 align:middle line:84% Otherwise, you risk distortion of optical images there. 00:29:43.870 --> 00:29:46.290 align:middle line:84% So over time, a time period of several years, 00:29:46.290 --> 00:29:50.110 align:middle line:84% these big mirrors, they can slowly deform, 00:29:50.110 --> 00:29:52.470 align:middle line:84% mostly due to gravitational force. 00:29:52.470 --> 00:29:56.910 align:middle line:84% So how do you measure this kind of a viscous flow 00:29:56.910 --> 00:29:59.830 align:middle line:84% in an instrument like this, where the viscosity is obviously 00:29:59.830 --> 00:30:00.870 align:middle line:90% very high? 00:30:00.870 --> 00:30:04.150 align:middle line:84% So the technique they use is basically optical interference. 00:30:04.150 --> 00:30:09.050 align:middle line:84% So what they will do, they can, for example, 00:30:09.050 --> 00:30:13.910 align:middle line:84% put the piece of glass you want to measure, 00:30:13.910 --> 00:30:16.790 align:middle line:84% you hold it on the side, and then 00:30:16.790 --> 00:30:19.080 align:middle line:84% you put it against the reference plate. 00:30:19.080 --> 00:30:21.720 align:middle line:84% So the bottom one, this will be your reference plate. 00:30:21.720 --> 00:30:22.800 align:middle line:90% And this is your sample. 00:30:22.800 --> 00:30:25.460 align:middle line:90% 00:30:25.460 --> 00:30:31.140 align:middle line:84% What you do, you then shine a light from on top. 00:30:31.140 --> 00:30:33.580 align:middle line:84% So then when light passes through this gap 00:30:33.580 --> 00:30:35.220 align:middle line:84% in between these two samples here, 00:30:35.220 --> 00:30:37.140 align:middle line:84% it can bounce back and forth many times 00:30:37.140 --> 00:30:39.660 align:middle line:84% between the sample and the reference plate. 00:30:39.660 --> 00:30:41.780 align:middle line:84% And then depending on whether you 00:30:41.780 --> 00:30:44.380 align:middle line:84% get integral, multiple wavelengths or maybe 00:30:44.380 --> 00:30:46.520 align:middle line:84% half-integral or multiple wavelengths, 00:30:46.520 --> 00:30:49.420 align:middle line:84% you can get constructive versus destructive interference. 00:30:49.420 --> 00:30:53.180 align:middle line:84% So if you use a white light to shine through this plate here, 00:30:53.180 --> 00:30:55.860 align:middle line:84% some wavelengths constructively interfere, some wavelengths 00:30:55.860 --> 00:30:57.220 align:middle line:90% destructively interfere. 00:30:57.220 --> 00:31:01.380 align:middle line:84% So you actually see color in the reflected image. 00:31:01.380 --> 00:31:04.020 align:middle line:84% So this is very similar to when you have 00:31:04.020 --> 00:31:05.235 align:middle line:90% oil films spreading on water. 00:31:05.235 --> 00:31:07.360 align:middle line:84% And then you see this kind of color oil film there. 00:31:07.360 --> 00:31:07.860 align:middle line:90% Same idea. 00:31:07.860 --> 00:31:09.500 align:middle line:84% This is basically called interference. 00:31:09.500 --> 00:31:11.980 align:middle line:84% So from the color fringe, you can now 00:31:11.980 --> 00:31:16.420 align:middle line:84% infer what is the gap width between these two pieces 00:31:16.420 --> 00:31:18.180 align:middle line:84% here with very high precision, down to, 00:31:18.180 --> 00:31:21.340 align:middle line:84% like, single-digit-- a few nanometers of precision. 00:31:21.340 --> 00:31:23.660 align:middle line:84% So now with this technique, you can then 00:31:23.660 --> 00:31:26.500 align:middle line:84% carry out this measurement over an extended period of time 00:31:26.500 --> 00:31:30.100 align:middle line:84% to determine what is the viscosity at this high viscosity 00:31:30.100 --> 00:31:30.807 align:middle line:90% range. 00:31:30.807 --> 00:31:31.640 align:middle line:90% So I'm quoting here. 00:31:31.640 --> 00:31:33.700 align:middle line:84% This is basically from one paper. 00:31:33.700 --> 00:31:35.620 align:middle line:84% The authors perform the measurement 00:31:35.620 --> 00:31:37.940 align:middle line:90% over a period of six years. 00:31:37.940 --> 00:31:39.740 align:middle line:84% And they were able to measure deformation 00:31:39.740 --> 00:31:42.220 align:middle line:84% of the order of a few nanometers to calculate 00:31:42.220 --> 00:31:46.120 align:middle line:84% viscosity of the order of 10 to 15, 16, 17 Pascal-second. 00:31:46.120 --> 00:31:49.040 align:middle line:90% 00:31:49.040 --> 00:31:49.540 align:middle line:90% Yes. 00:31:49.540 --> 00:31:52.340 align:middle line:84% Again, not a very good topic for PhD 00:31:52.340 --> 00:31:55.320 align:middle line:84% thesis, but you know, six years, maybe tolerable. 00:31:55.320 --> 00:31:59.540 align:middle line:84% Better than the pitch drop experiment. 00:31:59.540 --> 00:32:01.712 align:middle line:84% You get one paper after six years? 00:32:01.712 --> 00:32:02.920 align:middle line:90% That's actually a true story. 00:32:02.920 --> 00:32:06.093 align:middle line:84% I was actually at a glass conference. 00:32:06.093 --> 00:32:08.260 align:middle line:84% Someone was-- the thesis topic was actually studying 00:32:08.260 --> 00:32:10.705 align:middle line:90% glass aging or relaxation. 00:32:10.705 --> 00:32:12.580 align:middle line:84% So they actually inherited a bunch of samples 00:32:12.580 --> 00:32:15.295 align:middle line:90% from previous PhD students. 00:32:15.295 --> 00:32:17.420 align:middle line:84% And then they actually measured all the properties. 00:32:17.420 --> 00:32:20.920 align:middle line:84% And then studying why you have this kind of relaxation. 00:32:20.920 --> 00:32:23.260 align:middle line:84% So yeah, some of these long-term experiments 00:32:23.260 --> 00:32:24.820 align:middle line:90% can be legit PhD topics. 00:32:24.820 --> 00:32:27.740 align:middle line:84% But it requires transition of samples 00:32:27.740 --> 00:32:29.760 align:middle line:84% between different generations of PhD students. 00:32:29.760 --> 00:32:32.900 align:middle line:90% 00:32:32.900 --> 00:32:36.700 align:middle line:84% So now if we are now able to measure or characterize 00:32:36.700 --> 00:32:39.537 align:middle line:84% the viscosity of glasses, even to this very high range there, 00:32:39.537 --> 00:32:41.620 align:middle line:84% we can now come back to the question we have asked 00:32:41.620 --> 00:32:42.920 align:middle line:90% in the beginning of the class. 00:32:42.920 --> 00:32:48.540 align:middle line:84% So is glass a solid or a viscous fluid? 00:32:48.540 --> 00:32:51.740 align:middle line:84% Is the flow of glass completely negligible 00:32:51.740 --> 00:32:54.083 align:middle line:90% under ambient conditions? 00:32:54.083 --> 00:32:55.500 align:middle line:84% So this question has actually been 00:32:55.500 --> 00:32:57.460 align:middle line:90% investigated by a few authors. 00:32:57.460 --> 00:32:59.620 align:middle line:84% This is one of the most recent attempts 00:32:59.620 --> 00:33:02.040 align:middle line:84% that people from a group of scientists from Corning, 00:33:02.040 --> 00:33:03.940 align:middle line:84% they actually performed some calculations. 00:33:03.940 --> 00:33:07.340 align:middle line:84% Essentially, they experimentally measured the viscosity of glass 00:33:07.340 --> 00:33:10.000 align:middle line:84% using whatever technique we mentioned there. 00:33:10.000 --> 00:33:11.780 align:middle line:84% Then they can extrapolate this viscosity 00:33:11.780 --> 00:33:14.718 align:middle line:84% to room temperature using the [INAUDIBLE] equation. 00:33:14.718 --> 00:33:16.260 align:middle line:84% Remember the equation we talked about 00:33:16.260 --> 00:33:18.552 align:middle line:84% for how to describe viscosity dependent on temperature? 00:33:18.552 --> 00:33:20.415 align:middle line:84% So then they could use that to then infer 00:33:20.415 --> 00:33:22.540 align:middle line:84% what's the viscosity of glass, normal glass at room 00:33:22.540 --> 00:33:23.340 align:middle line:90% temperature. 00:33:23.340 --> 00:33:24.940 align:middle line:84% And then from that, they can then 00:33:24.940 --> 00:33:27.780 align:middle line:84% estimate what is the time that's needed 00:33:27.780 --> 00:33:32.460 align:middle line:84% to deform the glass, for example, for a few nanometers. 00:33:32.460 --> 00:33:36.560 align:middle line:84% And the conclusion there is that at room temperature, 00:33:36.560 --> 00:33:39.100 align:middle line:84% the viscosity is of the order of 10 to 24 to 10 00:33:39.100 --> 00:33:41.220 align:middle line:90% to the 25 Pascal-second. 00:33:41.220 --> 00:33:45.220 align:middle line:84% That's 12 orders of magnitude higher than glass transition 00:33:45.220 --> 00:33:46.100 align:middle line:90% temperature. 00:33:46.100 --> 00:33:47.940 align:middle line:84% And if you think about pitch, this 00:33:47.940 --> 00:33:50.340 align:middle line:84% is like 16 orders of magnitude higher viscosity compared 00:33:50.340 --> 00:33:52.060 align:middle line:90% to pitch. 00:33:52.060 --> 00:33:54.580 align:middle line:84% So it's not surprising that it would 00:33:54.580 --> 00:33:56.460 align:middle line:84% take some-- the conclusion here is 00:33:56.460 --> 00:33:59.380 align:middle line:84% that it takes a billion years to just 00:33:59.380 --> 00:34:03.900 align:middle line:84% have a maximum flow of order of about 1 nanometer. 00:34:03.900 --> 00:34:07.820 align:middle line:84% So conclusion-- glasses at room temperature-- 00:34:07.820 --> 00:34:09.280 align:middle line:90% I mean soda-lime glass. 00:34:09.280 --> 00:34:11.460 align:middle line:84% You're not talking about these low-Tg glasses. 00:34:11.460 --> 00:34:13.040 align:middle line:84% For things like soda-lime glasses, 00:34:13.040 --> 00:34:15.780 align:middle line:84% you can pretty much treat them just like [? electric ?] solids. 00:34:15.780 --> 00:34:19.540 align:middle line:84% The viscous behavior is pretty much completely negligible 00:34:19.540 --> 00:34:21.520 align:middle line:84% because it's extremely high viscosity. 00:34:21.520 --> 00:34:23.968 align:middle line:90% 00:34:23.968 --> 00:34:25.260 align:middle line:90% Now, you may have the question. 00:34:25.260 --> 00:34:28.120 align:middle line:84% For those medieval cathedral color windows, 00:34:28.120 --> 00:34:31.500 align:middle line:84% why the bottom tend to be wider than the top? 00:34:31.500 --> 00:34:33.060 align:middle line:84% The answer is actually quite simple. 00:34:33.060 --> 00:34:35.760 align:middle line:84% Because when the construction workers, when they assemble it, 00:34:35.760 --> 00:34:37.840 align:middle line:84% they know at the time the window is not uniform, 00:34:37.840 --> 00:34:38.960 align:middle line:90% thickness is not uniform. 00:34:38.960 --> 00:34:40.880 align:middle line:84% So in order to ensure mechanical stability, 00:34:40.880 --> 00:34:43.219 align:middle line:84% they tend to put the thicker side at the bottom, then 00:34:43.219 --> 00:34:46.380 align:middle line:90% the thinner side on top. 00:34:46.380 --> 00:34:49.020 align:middle line:84% Now, one of the examples to support this 00:34:49.020 --> 00:34:50.840 align:middle line:90% is that people do find mistakes. 00:34:50.840 --> 00:34:53.340 align:middle line:84% They do sometimes see these window 00:34:53.340 --> 00:34:56.155 align:middle line:84% pane glasses where the thicker side is actually on top. 00:34:56.155 --> 00:34:57.780 align:middle line:84% That's just because it's assembly error 00:34:57.780 --> 00:34:58.960 align:middle line:90% of the construction workers. 00:34:58.960 --> 00:35:01.500 align:middle line:90% 00:35:01.500 --> 00:35:05.140 align:middle line:84% So just to conclude what we have talked about here, 00:35:05.140 --> 00:35:07.660 align:middle line:90% I decided to put this quote-- 00:35:07.660 --> 00:35:11.802 align:middle line:84% "chocolate smells, flowers wilt, diamonds are forever." 00:35:11.802 --> 00:35:13.510 align:middle line:84% You can obviously see where this is from. 00:35:13.510 --> 00:35:16.450 align:middle line:84% This is from a shop that sells diamonds. 00:35:16.450 --> 00:35:18.070 align:middle line:84% But from what we have learned here, 00:35:18.070 --> 00:35:20.605 align:middle line:84% you see that glasses can do equally well. 00:35:20.605 --> 00:35:22.730 align:middle line:84% In fact, diamonds are not thermodynamically stable. 00:35:22.730 --> 00:35:24.605 align:middle line:84% Graphite is a thermodynamically stable state. 00:35:24.605 --> 00:35:27.690 align:middle line:90% So glasses are forever. 00:35:27.690 --> 00:35:29.230 align:middle line:90% So forget about diamond rings. 00:35:29.230 --> 00:35:31.330 align:middle line:84% I think glass rings can work equally well. 00:35:31.330 --> 00:35:33.970 align:middle line:90% OK. 00:35:33.970 --> 00:35:35.150 align:middle line:90% Think twice about it. 00:35:35.150 --> 00:35:39.170 align:middle line:90% 00:35:39.170 --> 00:35:40.290 align:middle line:90% That's the next chapter. 00:35:40.290 --> 00:35:42.415 align:middle line:84% We're going to talk about mechanical property next. 00:35:42.415 --> 00:35:43.242 align:middle line:90% So hold on to that. 00:35:43.242 --> 00:35:45.450 align:middle line:84% You are going to see some surprising numbers there as 00:35:45.450 --> 00:35:45.950 align:middle line:90% well. 00:35:45.950 --> 00:35:50.530 align:middle line:84% Glasses are also pretty good in terms of mechanical properties. 00:35:50.530 --> 00:35:51.750 align:middle line:90% You should be more precise. 00:35:51.750 --> 00:35:54.770 align:middle line:84% It's a hardness that really makes a difference. 00:35:54.770 --> 00:35:57.210 align:middle line:84% Mechanical properties-- glasses are quite good as long 00:35:57.210 --> 00:36:00.290 align:middle line:90% as they are defect-free. 00:36:00.290 --> 00:36:01.170 align:middle line:90% OK. 00:36:01.170 --> 00:36:03.850 align:middle line:84% So just to quickly summarize what we have talked about here, 00:36:03.850 --> 00:36:06.076 align:middle line:84% we have discussed about two kinds 00:36:06.076 --> 00:36:09.230 align:middle line:84% of contrasting phenomena-- elasticity and viscosity. 00:36:09.230 --> 00:36:11.770 align:middle line:84% We talked about elasticity being instantaneous. 00:36:11.770 --> 00:36:15.450 align:middle line:84% Viscosity, the key point here is that it's rate-dependent. 00:36:15.450 --> 00:36:18.210 align:middle line:84% It's permanent but then the shear stress 00:36:18.210 --> 00:36:20.270 align:middle line:84% depends on the shear strain rate. 00:36:20.270 --> 00:36:24.610 align:middle line:84% So these come from different microscopic mechanisms 00:36:24.610 --> 00:36:26.250 align:middle line:90% of viscosity versus elasticity. 00:36:26.250 --> 00:36:29.050 align:middle line:84% Elasticity comes from the repulsive and attractive forces 00:36:29.050 --> 00:36:30.030 align:middle line:90% between molecules. 00:36:30.030 --> 00:36:32.570 align:middle line:84% And that's why they become very temperature-insensitive. 00:36:32.570 --> 00:36:37.410 align:middle line:84% Versus viscosity always involves relative motion 00:36:37.410 --> 00:36:40.650 align:middle line:84% of molecules or atoms with respect to each other. 00:36:40.650 --> 00:36:45.270 align:middle line:84% So once you involve motion of atoms or molecules, 00:36:45.270 --> 00:36:47.550 align:middle line:84% this tends to be a thermally activated process. 00:36:47.550 --> 00:36:50.810 align:middle line:84% And that's why you tend to see a large change of viscosity 00:36:50.810 --> 00:36:52.790 align:middle line:90% as a function of temperature. 00:36:52.790 --> 00:36:54.410 align:middle line:84% You describe the phenomena depending 00:36:54.410 --> 00:36:55.827 align:middle line:84% on whether you have a strong fluid 00:36:55.827 --> 00:36:57.590 align:middle line:90% or you have a fragile fluid. 00:36:57.590 --> 00:36:59.690 align:middle line:84% You can either use the Arrhenius equation or maybe 00:36:59.690 --> 00:37:03.530 align:middle line:84% the [INAUDIBLE] equation, or VFT equation for those kinds 00:37:03.530 --> 00:37:04.530 align:middle line:90% of behaviors there. 00:37:04.530 --> 00:37:08.890 align:middle line:84% And finally, we talked about this simple Newtonian model does 00:37:08.890 --> 00:37:10.510 align:middle line:90% not always hold for glasses. 00:37:10.510 --> 00:37:14.410 align:middle line:84% You can have a non-Newtonian viscous flow. 00:37:14.410 --> 00:37:17.530 align:middle line:84% So the viscosity actually depends on strain rate as well. 00:37:17.530 --> 00:37:20.090 align:middle line:90% 00:37:20.090 --> 00:37:24.050 align:middle line:84% So that's pretty much about the basic knowledge about viscosity 00:37:24.050 --> 00:37:24.550 align:middle line:90% there. 00:37:24.550 --> 00:37:26.650 align:middle line:84% Any questions before we move on to talk 00:37:26.650 --> 00:37:29.710 align:middle line:84% about how to apply the [? phantom ?] side 00:37:29.710 --> 00:37:33.850 align:middle line:84% we have learned into shaping glass products? 00:37:33.850 --> 00:37:36.950 align:middle line:90% Questions? 00:37:36.950 --> 00:37:38.450 align:middle line:90% All good? 00:37:38.450 --> 00:37:39.030 align:middle line:90% All right. 00:37:39.030 --> 00:37:40.750 align:middle line:90% So now glass shaping. 00:37:40.750 --> 00:37:43.225 align:middle line:90% 00:37:43.225 --> 00:37:45.350 align:middle line:84% Before I go in to talk about any technical details, 00:37:45.350 --> 00:37:46.930 align:middle line:84% I just want to show you this little paragraph, 00:37:46.930 --> 00:37:49.290 align:middle line:84% which I exerted from an online forum, where people 00:37:49.290 --> 00:37:52.370 align:middle line:84% are essentially asking questions about why people like 00:37:52.370 --> 00:37:54.730 align:middle line:84% to use glasses to make all different kinds 00:37:54.730 --> 00:37:56.270 align:middle line:90% of everyday products. 00:37:56.270 --> 00:37:58.570 align:middle line:84% What's the benefits there in terms of processing? 00:37:58.570 --> 00:38:00.770 align:middle line:90% So I quite like this quote here. 00:38:00.770 --> 00:38:03.410 align:middle line:84% It says that viscosity makes things happen essentially 00:38:03.410 --> 00:38:04.970 align:middle line:90% in slow motion. 00:38:04.970 --> 00:38:06.570 align:middle line:84% And this is a unique behavior that 00:38:06.570 --> 00:38:09.610 align:middle line:84% only exists in glass, where you have this continuous viscosity 00:38:09.610 --> 00:38:10.950 align:middle line:90% temperature behavior. 00:38:10.950 --> 00:38:13.090 align:middle line:84% So you can tune viscosity precisely with respect 00:38:13.090 --> 00:38:14.570 align:middle line:90% to temperature. 00:38:14.570 --> 00:38:18.050 align:middle line:84% So to illustrate the difference here 00:38:18.050 --> 00:38:21.930 align:middle line:84% between a crystalline material and glass, let's think about-- 00:38:21.930 --> 00:38:24.430 align:middle line:84% let's say this is, for example, volume versus temperature. 00:38:24.430 --> 00:38:27.970 align:middle line:84% This is a curve we have seen many, many times. 00:38:27.970 --> 00:38:32.530 align:middle line:84% So if it's a crystalline material, then what you will get 00:38:32.530 --> 00:38:34.850 align:middle line:90% is a curve like this. 00:38:34.850 --> 00:38:38.770 align:middle line:84% You have a liquid state, but when you get to melting point, 00:38:38.770 --> 00:38:43.690 align:middle line:84% abruptly, you suddenly change from a solid into a liquid. 00:38:43.690 --> 00:38:47.610 align:middle line:84% So there's a very large switch of the deformation behavior 00:38:47.610 --> 00:38:48.510 align:middle line:90% of the material. 00:38:48.510 --> 00:38:52.010 align:middle line:84% Liquid tend to have a low viscosity. 00:38:52.010 --> 00:38:54.150 align:middle line:84% So as a result, things start to chip away. 00:38:54.150 --> 00:38:55.530 align:middle line:90% That's what I'm showing there. 00:38:55.530 --> 00:38:58.490 align:middle line:84% Essentially, you cannot hold the shape when it goes through this 00:38:58.490 --> 00:39:00.170 align:middle line:90% abrupt transition there. 00:39:00.170 --> 00:39:03.130 align:middle line:84% Glass, on the other hand, you have a continuous viscosity 00:39:03.130 --> 00:39:03.985 align:middle line:90% temperature curve. 00:39:03.985 --> 00:39:05.610 align:middle line:84% As you go through this glass transition 00:39:05.610 --> 00:39:08.230 align:middle line:84% here, by controlling temperature, 00:39:08.230 --> 00:39:10.410 align:middle line:84% you can quite precisely determine 00:39:10.410 --> 00:39:15.410 align:middle line:84% the viscosity of the glass melt. And by choosing a glass melt 00:39:15.410 --> 00:39:18.170 align:middle line:84% with appropriate viscosity, you can ensure that you can easily 00:39:18.170 --> 00:39:20.360 align:middle line:84% deform it, but yet it can also hold 00:39:20.360 --> 00:39:22.110 align:middle line:84% its shape, in that it's not dripping away, 00:39:22.110 --> 00:39:23.970 align:middle line:90% it's not collapsing. 00:39:23.970 --> 00:39:25.230 align:middle line:90% That's what is put here. 00:39:25.230 --> 00:39:29.130 align:middle line:84% So if it's a crystalline solid, as soon 00:39:29.130 --> 00:39:31.130 align:middle line:84% as you reach the melting point, a drop of liquid 00:39:31.130 --> 00:39:34.090 align:middle line:84% forms and falls away from the melting surface. 00:39:34.090 --> 00:39:36.290 align:middle line:84% Glass, on the other hand, can gradually 00:39:36.290 --> 00:39:39.770 align:middle line:84% transform from a high solid to a slowly softening liquid. 00:39:39.770 --> 00:39:42.410 align:middle line:84% And the liquid now allows you to-- 00:39:42.410 --> 00:39:45.170 align:middle line:84% it gradually stiffens as it cools, because the viscosity 00:39:45.170 --> 00:39:45.930 align:middle line:90% increases. 00:39:45.930 --> 00:39:49.368 align:middle line:84% And it gives you a window to allow glass workers 00:39:49.368 --> 00:39:51.410 align:middle line:84% to then process it into different kinds of shapes 00:39:51.410 --> 00:39:53.250 align:middle line:90% by manipulating it. 00:39:53.250 --> 00:39:55.810 align:middle line:84% So the key takeaway message here is 00:39:55.810 --> 00:39:57.770 align:middle line:84% that this continuous viscosity temperature 00:39:57.770 --> 00:39:59.870 align:middle line:90% curve is really important. 00:39:59.870 --> 00:40:02.290 align:middle line:84% That underlies the process versatility 00:40:02.290 --> 00:40:04.190 align:middle line:90% of amorphous glass materials. 00:40:04.190 --> 00:40:08.490 align:middle line:90% 00:40:08.490 --> 00:40:12.430 align:middle line:84% I just also want to mention that in a couple of weeks, 00:40:12.430 --> 00:40:15.250 align:middle line:84% we're going to have a demo session at the MIT Glass Lab. 00:40:15.250 --> 00:40:21.330 align:middle line:84% You can find the date on the first slide deck in the class 00:40:21.330 --> 00:40:21.830 align:middle line:90% there. 00:40:21.830 --> 00:40:23.550 align:middle line:84% It's basically the first lesson in March. 00:40:23.550 --> 00:40:26.510 align:middle line:84% So we are going to meet directly at the MIT Glass Lab. 00:40:26.510 --> 00:40:28.330 align:middle line:84% We are going to show some demos about how 00:40:28.330 --> 00:40:32.770 align:middle line:84% to use this viscous flow behavior to shape 00:40:32.770 --> 00:40:34.090 align:middle line:90% different glass products. 00:40:34.090 --> 00:40:37.830 align:middle line:90% 00:40:37.830 --> 00:40:40.388 align:middle line:84% So as I promised you, I'm going to show you this plot again, 00:40:40.388 --> 00:40:42.930 align:middle line:84% because this is actually quite important to glass processing. 00:40:42.930 --> 00:40:46.690 align:middle line:84% Key takeaway message is that most of the glass processes 00:40:46.690 --> 00:40:49.010 align:middle line:84% takes place in this working range, where 00:40:49.010 --> 00:40:51.730 align:middle line:84% you have a chewing gum-like fluids that you can easily 00:40:51.730 --> 00:40:53.450 align:middle line:90% shape and deform. 00:40:53.450 --> 00:40:55.490 align:middle line:84% You do notice here that this float glass 00:40:55.490 --> 00:40:58.137 align:middle line:84% goes in the relatively low viscosity end. 00:40:58.137 --> 00:40:59.970 align:middle line:84% And that's because in a float glass process, 00:40:59.970 --> 00:41:01.845 align:middle line:84% we're going to talk about it in a few slides, 00:41:01.845 --> 00:41:04.760 align:middle line:84% is when you have molten glass floating on a tin bath 00:41:04.760 --> 00:41:07.900 align:middle line:84% to get large, flat sheets, because in this case, 00:41:07.900 --> 00:41:09.240 align:middle line:90% the glass needs to flow. 00:41:09.240 --> 00:41:12.440 align:middle line:84% So that's why people like to do it at slightly lower viscosity 00:41:12.440 --> 00:41:13.040 align:middle line:90% points. 00:41:13.040 --> 00:41:17.720 align:middle line:84% Now, this one, this is precision glass molding. 00:41:17.720 --> 00:41:19.560 align:middle line:84% So precision glass molding takes place 00:41:19.560 --> 00:41:21.920 align:middle line:84% at higher viscosity ranges, sometimes right 00:41:21.920 --> 00:41:23.520 align:middle line:90% outside the working range. 00:41:23.520 --> 00:41:26.960 align:middle line:84% Because unlike other processes here, precision glass molding, 00:41:26.960 --> 00:41:30.060 align:middle line:90% you apply very large pressure. 00:41:30.060 --> 00:41:31.800 align:middle line:84% If you apply large pressure, we know 00:41:31.800 --> 00:41:33.880 align:middle line:84% that the shear rate depends on-- it linearly 00:41:33.880 --> 00:41:35.532 align:middle line:90% scales with shear stress. 00:41:35.532 --> 00:41:37.240 align:middle line:84% So high stress essentially means that you 00:41:37.240 --> 00:41:39.920 align:middle line:84% can afford to have low viscosity while still maintaining 00:41:39.920 --> 00:41:41.880 align:middle line:90% a decent stress rate. 00:41:41.880 --> 00:41:45.020 align:middle line:84% So basically, pressure expedites the process. 00:41:45.020 --> 00:41:49.400 align:middle line:84% That's why you can afford to have a higher pressure there. 00:41:49.400 --> 00:41:52.280 align:middle line:90% Now, last one. 00:41:52.280 --> 00:41:54.440 align:middle line:90% Annealing Lehr. 00:41:54.440 --> 00:41:57.273 align:middle line:84% Lehr is basically just another name of "furnace." 00:41:57.273 --> 00:41:59.440 align:middle line:84% So when we talk about glass shaping in this chapter, 00:41:59.440 --> 00:42:01.440 align:middle line:84% you're going to see a lot of terminologies 00:42:01.440 --> 00:42:03.945 align:middle line:84% that's pretty unique only to glass processing. 00:42:03.945 --> 00:42:05.320 align:middle line:84% "Lehr" is one of them, but "Lehr" 00:42:05.320 --> 00:42:07.278 align:middle line:84% basically is just a furnace, annealing furnace. 00:42:07.278 --> 00:42:10.520 align:middle line:84% In a Lehr, you anneal the glass, so it releases 00:42:10.520 --> 00:42:11.700 align:middle line:90% any kind of internal stress. 00:42:11.700 --> 00:42:14.480 align:middle line:84% So prevent any premature cracking of the glass products 00:42:14.480 --> 00:42:17.280 align:middle line:90% during usage. 00:42:17.280 --> 00:42:21.400 align:middle line:84% So now, in this slide, I'm summarizing 00:42:21.400 --> 00:42:23.440 align:middle line:84% the typical viscosity reference points 00:42:23.440 --> 00:42:25.040 align:middle line:84% for different conditional glasses-- 00:42:25.040 --> 00:42:27.880 align:middle line:84% soda-lime, borosilicate, fused silica. 00:42:27.880 --> 00:42:31.960 align:middle line:84% Takeaway message-- fused silica, you see this temperature, 00:42:31.960 --> 00:42:34.060 align:middle line:84% it's softening point is very high, 00:42:34.060 --> 00:42:37.360 align:middle line:84% working point is basically absent. 00:42:37.360 --> 00:42:38.580 align:middle line:90% Its temperature is too high. 00:42:38.580 --> 00:42:42.960 align:middle line:84% So that's why, as I said, nobody really processes fused silica. 00:42:42.960 --> 00:42:45.200 align:middle line:84% You can get them, they get quite expensive. 00:42:45.200 --> 00:42:47.495 align:middle line:84% Borosilicate, due to a higher network connectivity, 00:42:47.495 --> 00:42:49.120 align:middle line:84% all of this temperature reference point 00:42:49.120 --> 00:42:51.960 align:middle line:84% is actually higher than the corresponding soda-lime glass. 00:42:51.960 --> 00:42:55.600 align:middle line:84% They also have a much lower coefficient 00:42:55.600 --> 00:42:58.040 align:middle line:90% of thermal expansion. 00:42:58.040 --> 00:42:59.920 align:middle line:84% So that's why, when you're trying 00:42:59.920 --> 00:43:01.840 align:middle line:84% to make borosilicate products, you 00:43:01.840 --> 00:43:03.760 align:middle line:84% can make it in the glass workshop, 00:43:03.760 --> 00:43:06.000 align:middle line:84% but it becomes very difficult if you're 00:43:06.000 --> 00:43:10.705 align:middle line:84% trying to mix soda-lime glass with borosilicate glass. 00:43:10.705 --> 00:43:12.580 align:middle line:84% Because when you're processing these glasses, 00:43:12.580 --> 00:43:14.520 align:middle line:84% when you're shaping them, you do it at a high temperature. 00:43:14.520 --> 00:43:15.937 align:middle line:84% If you're trying to fuse something 00:43:15.937 --> 00:43:18.000 align:middle line:84% together, then, as you cool down, 00:43:18.000 --> 00:43:20.000 align:middle line:84% due to the large CTE mismatch, you 00:43:20.000 --> 00:43:24.080 align:middle line:84% accumulate a huge thermal stress in between the soda-lime glass 00:43:24.080 --> 00:43:25.280 align:middle line:90% and borosilicate glass. 00:43:25.280 --> 00:43:27.400 align:middle line:84% And that tends to actually fracture. 00:43:27.400 --> 00:43:29.350 align:middle line:84% In fact, when you go to a glass workshop, 00:43:29.350 --> 00:43:31.100 align:middle line:84% you're going to do one of the demos there, 00:43:31.100 --> 00:43:34.620 align:middle line:84% we're going to draw canes out of both borosilicate and soda-lime, 00:43:34.620 --> 00:43:36.560 align:middle line:84% essentially long glass, thin glass wires. 00:43:36.560 --> 00:43:38.820 align:middle line:84% We are then trying to fuse two canes together, 00:43:38.820 --> 00:43:40.945 align:middle line:90% borosilicate with the soda-lime. 00:43:40.945 --> 00:43:43.320 align:middle line:84% And once it cools down, you'll notice that it immediately 00:43:43.320 --> 00:43:45.880 align:middle line:84% bends, much like a bimetallic strip, 00:43:45.880 --> 00:43:48.360 align:middle line:84% and it eventually cracks into small pieces. 00:43:48.360 --> 00:43:52.800 align:middle line:84% So you're going to see that when we go to the glass shop demo. 00:43:52.800 --> 00:43:54.640 align:middle line:90% All right. 00:43:54.640 --> 00:43:56.660 align:middle line:90% Questions? 00:43:56.660 --> 00:43:57.280 align:middle line:90% OK. 00:43:57.280 --> 00:43:59.837 align:middle line:84% So in the next few slides in this part here, 00:43:59.837 --> 00:44:01.920 align:middle line:84% I'm going to show you a few processes-- how people 00:44:01.920 --> 00:44:04.003 align:middle line:84% use to actually shape glasses into different kinds 00:44:04.003 --> 00:44:05.240 align:middle line:90% of products. 00:44:05.240 --> 00:44:08.720 align:middle line:84% The earliest process that people do for the common glass form 00:44:08.720 --> 00:44:11.840 align:middle line:84% factor, which is flat glass, like window pane glass. 00:44:11.840 --> 00:44:13.520 align:middle line:84% The earliest process people developed 00:44:13.520 --> 00:44:17.560 align:middle line:90% is so-called crown glass. 00:44:17.560 --> 00:44:21.600 align:middle line:84% So crown glass, you have a big bubble of molten glass. 00:44:21.600 --> 00:44:24.520 align:middle line:84% You open the hole there at the end, 00:44:24.520 --> 00:44:26.640 align:middle line:90% so it becomes a big, flat piece. 00:44:26.640 --> 00:44:28.200 align:middle line:90% And then you start to spin. 00:44:28.200 --> 00:44:31.560 align:middle line:84% You put it onto a little steel rod. 00:44:31.560 --> 00:44:33.240 align:middle line:84% At the end, this is your glass piece. 00:44:33.240 --> 00:44:35.680 align:middle line:84% You start to spin it, so then this glass piece 00:44:35.680 --> 00:44:36.780 align:middle line:90% starts to rotate. 00:44:36.780 --> 00:44:40.140 align:middle line:84% And due to the centrifuge force, it forms this thin, flat sheet. 00:44:40.140 --> 00:44:43.400 align:middle line:84% So like a cylindrical, big, thin, flat sheet. 00:44:43.400 --> 00:44:45.440 align:middle line:84% So you can then use that to actually create 00:44:45.440 --> 00:44:48.260 align:middle line:84% this-- cut it and create this kind of flat glass panels there. 00:44:48.260 --> 00:44:50.200 align:middle line:84% But then you notice, obviously, this process 00:44:50.200 --> 00:44:51.840 align:middle line:90% is not very well controlled. 00:44:51.840 --> 00:44:55.120 align:middle line:84% You see that there's actually a big defect right in the center. 00:44:55.120 --> 00:44:57.900 align:middle line:84% This is where your glass rose, or pontil, 00:44:57.900 --> 00:45:00.240 align:middle line:84% as the glass workers call it, comes into contact 00:45:00.240 --> 00:45:01.640 align:middle line:90% with the glass piece. 00:45:01.640 --> 00:45:03.590 align:middle line:90% OK. 00:45:03.590 --> 00:45:07.128 align:middle line:84% AUDIENCE: Is it like pizza spinning? 00:45:07.128 --> 00:45:07.920 align:middle line:90% PROFESSOR: Similar. 00:45:07.920 --> 00:45:08.820 align:middle line:90% Very similar to that. 00:45:08.820 --> 00:45:11.040 align:middle line:90% Yeah. 00:45:11.040 --> 00:45:12.860 align:middle line:90% You are doing it this way, OK? 00:45:12.860 --> 00:45:14.140 align:middle line:90% And you're just rotating it. 00:45:14.140 --> 00:45:15.320 align:middle line:90% Yeah. 00:45:15.320 --> 00:45:17.320 align:middle line:84% So in fact, I was looking at some Instagrams. 00:45:17.320 --> 00:45:19.320 align:middle line:84% They have pictures of this [INAUDIBLE] glassware 00:45:19.320 --> 00:45:20.897 align:middle line:84% of preparing for a glass lecture. 00:45:20.897 --> 00:45:23.480 align:middle line:84% And people were commenting here, like, whoa, this glass window 00:45:23.480 --> 00:45:24.340 align:middle line:90% looks so cute. 00:45:24.340 --> 00:45:27.910 align:middle line:84% Why you only see in Europe and not in the US? 00:45:27.910 --> 00:45:29.660 align:middle line:84% Because we don't have those old buildings. 00:45:29.660 --> 00:45:30.760 align:middle line:90% That's it. 00:45:30.760 --> 00:45:37.000 align:middle line:84% We all use a newer process to actually make the windows. 00:45:37.000 --> 00:45:40.200 align:middle line:84% So one of the standard process that people 00:45:40.200 --> 00:45:42.960 align:middle line:84% use today to make large flat glass sheet, 00:45:42.960 --> 00:45:45.080 align:middle line:84% this is called float glass process. 00:45:45.080 --> 00:45:50.180 align:middle line:84% So what I'm illustrating here is a continuous process flow-- 00:45:50.180 --> 00:45:53.320 align:middle line:84% how people actually manufacture this kind of flat glasses here. 00:45:53.320 --> 00:45:54.940 align:middle line:90% It's all a continuous process. 00:45:54.940 --> 00:45:56.910 align:middle line:84% You started out from feeding the raw material 00:45:56.910 --> 00:45:59.390 align:middle line:84% all the way to coming out, having glass sheets coming out 00:45:59.390 --> 00:46:00.210 align:middle line:90% continuously. 00:46:00.210 --> 00:46:02.750 align:middle line:90% And non-stop. 00:46:02.750 --> 00:46:03.783 align:middle line:90% 24/7. 00:46:03.783 --> 00:46:05.450 align:middle line:84% It's a continuous manufacturing process. 00:46:05.450 --> 00:46:08.070 align:middle line:84% So basically, the process involves 00:46:08.070 --> 00:46:10.630 align:middle line:84% starting with mixing different kinds of ingredients. 00:46:10.630 --> 00:46:15.270 align:middle line:84% So for soda-lime glasses, the ingredient would be sand, SiO2. 00:46:15.270 --> 00:46:22.470 align:middle line:84% You have soda, which is sodium carbonate, for example. 00:46:22.470 --> 00:46:26.830 align:middle line:84% You also have some minerals that actually contain calcium oxide, 00:46:26.830 --> 00:46:28.190 align:middle line:90% like dolomite. 00:46:28.190 --> 00:46:29.550 align:middle line:90% OK. 00:46:29.550 --> 00:46:33.710 align:middle line:84% That gives you the rare earth element. 00:46:33.710 --> 00:46:38.410 align:middle line:84% And then finally, you also add some broken glasses, 00:46:38.410 --> 00:46:40.030 align:middle line:90% used glasses. 00:46:40.030 --> 00:46:44.130 align:middle line:84% Those used glasses are called cullets. 00:46:44.130 --> 00:46:48.310 align:middle line:90% 00:46:48.310 --> 00:46:49.250 align:middle line:90% OK. 00:46:49.250 --> 00:46:50.590 align:middle line:90% This is a name to use-- 00:46:50.590 --> 00:46:53.910 align:middle line:84% you put some weighted glasses into your feeding material, 00:46:53.910 --> 00:46:55.110 align:middle line:90% into the furnace. 00:46:55.110 --> 00:46:56.730 align:middle line:84% Now, this is actually quite important. 00:46:56.730 --> 00:46:58.350 align:middle line:84% Why do they need to put cullets there? 00:46:58.350 --> 00:47:00.142 align:middle line:84% Because if you think about it, if you don't 00:47:00.142 --> 00:47:01.558 align:middle line:84% need to have the cullets, you just 00:47:01.558 --> 00:47:03.370 align:middle line:84% have all the raw minerals coming in there, 00:47:03.370 --> 00:47:06.770 align:middle line:84% they're all solid, crystalline solid-- in order to melt it, 00:47:06.770 --> 00:47:09.350 align:middle line:84% you need to go all the way to the melting point, 00:47:09.350 --> 00:47:12.270 align:middle line:84% and then you start forming the liquid phase. 00:47:12.270 --> 00:47:15.510 align:middle line:84% On the other hand, if you have cullets, they are glasses. 00:47:15.510 --> 00:47:17.590 align:middle line:84% It means that they start to soften, 00:47:17.590 --> 00:47:21.150 align:middle line:84% and you form an early liquid phase well before you actually 00:47:21.150 --> 00:47:24.270 align:middle line:90% reach the melting point. 00:47:24.270 --> 00:47:27.430 align:middle line:84% Now, that's important because for any kind 00:47:27.430 --> 00:47:30.270 align:middle line:84% of solid-state reaction, diffusion 00:47:30.270 --> 00:47:31.830 align:middle line:84% or any kind of transport phenomena 00:47:31.830 --> 00:47:33.870 align:middle line:84% always happens a lot faster in the liquid phase 00:47:33.870 --> 00:47:35.930 align:middle line:84% compared to the solid phase, which makes a lot of sense. 00:47:35.930 --> 00:47:37.490 align:middle line:84% Liquid phase molecules move around. 00:47:37.490 --> 00:47:39.270 align:middle line:84% So of course, you can get much higher 00:47:39.270 --> 00:47:42.650 align:middle line:84% molecular transport or reaction compared to any solid. 00:47:42.650 --> 00:47:45.390 align:middle line:84% So having these cullets allows you 00:47:45.390 --> 00:47:48.070 align:middle line:84% to form this early liquid phase, and that 00:47:48.070 --> 00:47:51.972 align:middle line:84% helps you to reduce the energy consumption in the process. 00:47:51.972 --> 00:47:53.430 align:middle line:84% You don't have to melt the material 00:47:53.430 --> 00:47:56.610 align:middle line:84% all the way by going all the way up to the melting point. 00:47:56.610 --> 00:47:59.110 align:middle line:84% So then you can significantly cut down the power consumption 00:47:59.110 --> 00:48:01.750 align:middle line:84% by something like 20% by just adding cullets 00:48:01.750 --> 00:48:02.930 align:middle line:90% into the process there. 00:48:02.930 --> 00:48:04.870 align:middle line:84% So that's why waste glasses is actually 00:48:04.870 --> 00:48:09.230 align:middle line:90% quite important ingredient. 00:48:09.230 --> 00:48:10.710 align:middle line:84% In fact, I have seen people doing-- 00:48:10.710 --> 00:48:12.710 align:middle line:84% they do internship at glass products. 00:48:12.710 --> 00:48:14.570 align:middle line:84% They make glass bottles and stuff. 00:48:14.570 --> 00:48:16.528 align:middle line:84% If they see any glass bottles that's defective, 00:48:16.528 --> 00:48:18.070 align:middle line:84% they don't try to fix it or anything. 00:48:18.070 --> 00:48:20.110 align:middle line:84% Just take it out, throw it into a cullet piece, 00:48:20.110 --> 00:48:21.490 align:middle line:90% because they need it anyway. 00:48:21.490 --> 00:48:21.990 align:middle line:90% Yeah. 00:48:21.990 --> 00:48:24.590 align:middle line:90% 00:48:24.590 --> 00:48:25.090 align:middle line:90% OK. 00:48:25.090 --> 00:48:28.380 align:middle line:84% So then once you mix the material, you then melt it. 00:48:28.380 --> 00:48:30.380 align:middle line:84% And then the melting furnace has the liquid that 00:48:30.380 --> 00:48:32.150 align:middle line:90% then feed into a floating bath. 00:48:32.150 --> 00:48:35.990 align:middle line:84% So for the floating bath, you basically have molten tin. 00:48:35.990 --> 00:48:39.010 align:middle line:84% So molten tin has a density that's higher than glass melts. 00:48:39.010 --> 00:48:40.750 align:middle line:84% So then this molten glass is then 00:48:40.750 --> 00:48:43.070 align:middle line:90% going to float on top of tin. 00:48:43.070 --> 00:48:50.190 align:middle line:84% And now, due to the action of surface tension and gravity, 00:48:50.190 --> 00:48:53.030 align:middle line:84% then the liquid then spreads on top of this molten tin 00:48:53.030 --> 00:48:55.630 align:middle line:90% to form a flat glass surface. 00:48:55.630 --> 00:48:56.310 align:middle line:90% OK. 00:48:56.310 --> 00:48:59.450 align:middle line:84% At the end, when it comes out from this floating furnace 00:48:59.450 --> 00:49:04.870 align:middle line:84% there, then it enters into the annealing Lehr. 00:49:04.870 --> 00:49:08.830 align:middle line:84% So annealing Lehr then helps you to relax any internal stress 00:49:08.830 --> 00:49:11.630 align:middle line:84% inside this flat glass sheet before it really comes out 00:49:11.630 --> 00:49:13.190 align:middle line:90% from here to get your-- 00:49:13.190 --> 00:49:15.910 align:middle line:84% then it can be cut and packaged into all kinds of flat glass 00:49:15.910 --> 00:49:16.610 align:middle line:90% products. 00:49:16.610 --> 00:49:20.470 align:middle line:84% So what I will do next is I'm actually 00:49:20.470 --> 00:49:22.990 align:middle line:84% going to play a little YouTube video, which probably talks 00:49:22.990 --> 00:49:24.870 align:middle line:84% all about this process and gives you 00:49:24.870 --> 00:49:30.016 align:middle line:84% a visual feeling of how things are done much better than I do. 00:49:30.016 --> 00:49:31.990 align:middle line:90% [VIDEO PLAYBACK] 00:49:31.990 --> 00:49:34.390 align:middle line:84% - Today a modern float glass line 00:49:34.390 --> 00:49:38.310 align:middle line:84% produces an average of several hundred tons of glass each day. 00:49:38.310 --> 00:49:44.870 align:middle line:84% It runs 24 hours a day, 365 days a year for over 15 years. 00:49:44.870 --> 00:49:49.070 align:middle line:84% There are about 450 float glass lines around the world. 00:49:49.070 --> 00:49:52.430 align:middle line:84% Together, they produce more than a million tons of float glass 00:49:52.430 --> 00:49:54.130 align:middle line:90% worldwide every year. 00:49:54.130 --> 00:50:01.870 align:middle line:90% 00:50:01.870 --> 00:50:05.710 align:middle line:84% Until the 1960s, flat glass was produced using the sheet 00:50:05.710 --> 00:50:08.150 align:middle line:84% and plate glass manufacturing process. 00:50:08.150 --> 00:50:11.390 align:middle line:84% This method was highly labor-intensive. 00:50:11.390 --> 00:50:13.610 align:middle line:84% Invented by Sir Alastair Pilkington, 00:50:13.610 --> 00:50:15.870 align:middle line:84% the float glass manufacturing process quickly 00:50:15.870 --> 00:50:18.190 align:middle line:84% became the universal method for producing 00:50:18.190 --> 00:50:21.230 align:middle line:90% high-quality flat glass. 00:50:21.230 --> 00:50:24.190 align:middle line:84% Today, float glass manufacturing supplies glass 00:50:24.190 --> 00:50:26.090 align:middle line:84% to a variety of different markets, 00:50:26.090 --> 00:50:29.530 align:middle line:84% including automotive, architectural, solar panel, 00:50:29.530 --> 00:50:32.190 align:middle line:84% and many other technical applications. 00:50:32.190 --> 00:50:34.910 align:middle line:84% Glassmaking uses some of the Earth's most abundant 00:50:34.910 --> 00:50:36.270 align:middle line:90% raw materials. 00:50:36.270 --> 00:50:38.630 align:middle line:84% The primary ingredient is sand, accounting 00:50:38.630 --> 00:50:41.430 align:middle line:84% for 60% of what is called the batch. 00:50:41.430 --> 00:50:44.430 align:middle line:84% Lime and dolomite are added to assist the weathering properties 00:50:44.430 --> 00:50:47.430 align:middle line:84% of the finished glass, while soda and sulfate lower 00:50:47.430 --> 00:50:50.220 align:middle line:84% the temperature at which sand will melt. 00:50:50.220 --> 00:50:53.560 align:middle line:84% But glass itself is also an important ingredient. 00:50:53.560 --> 00:50:56.700 align:middle line:90% 00:50:56.700 --> 00:51:00.220 align:middle line:84% Broken glass, called cullet, is recovered from the manufacturing 00:51:00.220 --> 00:51:04.340 align:middle line:84% process and then crushed before being added to the batch. 00:51:04.340 --> 00:51:06.620 align:middle line:84% This further accelerates the melting process 00:51:06.620 --> 00:51:08.740 align:middle line:84% and reduces the amount of energy required 00:51:08.740 --> 00:51:11.660 align:middle line:90% for melting by up to a fifth. 00:51:11.660 --> 00:51:14.020 align:middle line:84% All raw materials are rigorously checked 00:51:14.020 --> 00:51:16.040 align:middle line:84% to ensure the purity of the batch. 00:51:16.040 --> 00:51:20.660 align:middle line:90% 00:51:20.660 --> 00:51:23.060 align:middle line:84% It is then fed automatically into the filling 00:51:23.060 --> 00:51:24.660 align:middle line:90% end of a furnace. 00:51:24.660 --> 00:51:28.180 align:middle line:84% Natural gas burned in preheated combustion air then heats 00:51:28.180 --> 00:51:31.100 align:middle line:84% the batch up to 2,800 degrees Fahrenheit. 00:51:31.100 --> 00:51:34.020 align:middle line:84% Once heated, the batch materials melt and change 00:51:34.020 --> 00:51:37.180 align:middle line:84% from a semi-molten state to molten glass. 00:51:37.180 --> 00:51:39.420 align:middle line:84% Melting, refining, and homogenizing 00:51:39.420 --> 00:51:41.860 align:middle line:84% take place within separate zones of the furnace. 00:51:41.860 --> 00:51:45.060 align:middle line:84% Processes within the furnaces are managed from the control 00:51:45.060 --> 00:51:50.380 align:middle line:84% room to ensure that the glass is homogeneous and free of bubbles. 00:51:50.380 --> 00:51:53.700 align:middle line:84% Inside the furnace, heat is applied from alternate sides 00:51:53.700 --> 00:51:55.900 align:middle line:90% in 15-minute cycles. 00:51:55.900 --> 00:51:58.460 align:middle line:84% This assists fuel efficiency by ensuring 00:51:58.460 --> 00:52:02.100 align:middle line:84% that combustion takes place in the presence of preheated air. 00:52:02.100 --> 00:52:06.540 align:middle line:84% This continuous melting process can last as long as 50 hours. 00:52:06.540 --> 00:52:08.820 align:middle line:84% The glass leaves the conditioning end of the melting 00:52:08.820 --> 00:52:12.020 align:middle line:84% zone at a temperature of 2,000 degrees Fahrenheit through 00:52:12.020 --> 00:52:15.140 align:middle line:84% a narrow canal, where it passes to the heart of the process, 00:52:15.140 --> 00:52:17.260 align:middle line:90% the tin bath. 00:52:17.260 --> 00:52:19.700 align:middle line:84% Molten glass enters the tin bath and floats 00:52:19.700 --> 00:52:23.780 align:middle line:84% on top of the more dense, molten tin like oil floating on water. 00:52:23.780 --> 00:52:26.820 align:middle line:84% Here, the glass spreads out, following the perfect flatness 00:52:26.820 --> 00:52:30.020 align:middle line:84% of the tin, so that the upper and lower surfaces of the glass 00:52:30.020 --> 00:52:32.380 align:middle line:84% remain absolutely flat and parallel 00:52:32.380 --> 00:52:34.780 align:middle line:84% with perfect spectral properties. 00:52:34.780 --> 00:52:36.620 align:middle line:84% The glass is made thicker by confining 00:52:36.620 --> 00:52:39.300 align:middle line:84% its initial outward spread over the tin. 00:52:39.300 --> 00:52:41.203 align:middle line:84% To make thinner glass, the top rollers 00:52:41.203 --> 00:52:42.620 align:middle line:84% controlling the width of the glass 00:52:42.620 --> 00:52:45.940 align:middle line:84% are sped up to produce a gentle stretching action. 00:52:45.940 --> 00:52:48.580 align:middle line:84% A controlled atmosphere of hydrogen and nitrogen 00:52:48.580 --> 00:52:52.580 align:middle line:84% within the bath prevents the tin from oxidizing. 00:52:52.580 --> 00:52:54.480 align:middle line:84% When it emerges from the tin bath, 00:52:54.480 --> 00:52:56.660 align:middle line:84% the glass is sufficiently hard so as not 00:52:56.660 --> 00:52:59.140 align:middle line:84% to be marked by the conveyor rollers. 00:52:59.140 --> 00:53:01.060 align:middle line:84% The float glass manufacturing process 00:53:01.060 --> 00:53:05.180 align:middle line:84% can produce clear, tinted, and coated glass products. 00:53:05.180 --> 00:53:07.340 align:middle line:84% Online pyrolytic hard coatings are 00:53:07.340 --> 00:53:10.260 align:middle line:84% produced by depositing microscopically thin layers 00:53:10.260 --> 00:53:13.540 align:middle line:84% of metallic oxides using the chemical vapor deposition 00:53:13.540 --> 00:53:15.500 align:middle line:90% process. 00:53:15.500 --> 00:53:18.540 align:middle line:84% This process produces extremely durable products 00:53:18.540 --> 00:53:23.300 align:middle line:84% that can be easily handled, cut, tempered, bent, and fabricated. 00:53:23.300 --> 00:53:26.180 align:middle line:84% Pyrolytic-coated glass include low-E coatings 00:53:26.180 --> 00:53:30.160 align:middle line:84% for solar and thermal control, self-cleaning, anti-reflective, 00:53:30.160 --> 00:53:32.620 align:middle line:84% and many other special applications. 00:53:32.620 --> 00:53:35.220 align:middle line:84% The glass now enters the annealing Lehr, 00:53:35.220 --> 00:53:39.460 align:middle line:84% where any stresses are removed by a controlled cooling process. 00:53:39.460 --> 00:53:42.980 align:middle line:84% In a length of over 800 feet, equivalent to three football 00:53:42.980 --> 00:53:47.340 align:middle line:84% fields, the glass is taken from 1,100 degrees Fahrenheit down 00:53:47.340 --> 00:53:48.460 align:middle line:90% to room temperature. 00:53:48.460 --> 00:53:51.800 align:middle line:84% At this stage, the glass is perfect. 00:53:51.800 --> 00:53:58.580 align:middle line:90% 00:53:58.580 --> 00:54:01.220 align:middle line:84% Now the glass is scored, so it can be 00:54:01.220 --> 00:54:04.580 align:middle line:90% snapped to predetermined sizes. 00:54:04.580 --> 00:54:08.500 align:middle line:84% Indentations left by the top rollers are removed on conveyors 00:54:08.500 --> 00:54:11.540 align:middle line:84% and sent to be reintroduced as cullet at the beginning 00:54:11.540 --> 00:54:12.920 align:middle line:90% of the melting process. 00:54:12.920 --> 00:54:16.980 align:middle line:90% 00:54:16.980 --> 00:54:19.840 align:middle line:84% After passing through the automatic handling stages, 00:54:19.840 --> 00:54:21.620 align:middle line:84% customers' orders, which might involve 00:54:21.620 --> 00:54:23.640 align:middle line:84% a range of thicknesses and sizes, 00:54:23.640 --> 00:54:26.640 align:middle line:84% as well as special coatings, are packaged for delivery. 00:54:26.640 --> 00:54:29.580 align:middle line:90% 00:54:29.580 --> 00:54:32.040 align:middle line:84% As a leading global glass manufacturer, 00:54:32.040 --> 00:54:35.380 align:middle line:84% the NSG Group provides one of the broadest ranges of-- 00:54:35.380 --> 00:54:36.275 align:middle line:90% [END PLAYBACK] 00:54:36.275 --> 00:54:38.900 align:middle line:84% PROFESSOR: OK, so basically you see the visuals of the process, 00:54:38.900 --> 00:54:41.233 align:middle line:84% yeah-- it's that the temperature monotonically decreases 00:54:41.233 --> 00:54:42.700 align:middle line:90% from one end to the other end. 00:54:42.700 --> 00:54:44.540 align:middle line:84% And then it's a continuous process that 00:54:44.540 --> 00:54:47.180 align:middle line:90% manufactures glass products. 00:54:47.180 --> 00:54:48.860 align:middle line:84% So one thing I also mentioned here 00:54:48.860 --> 00:54:50.902 align:middle line:84% is about the ingredient they have mentioned here. 00:54:50.902 --> 00:54:52.820 align:middle line:84% They talk about dolomite increasing weathering 00:54:52.820 --> 00:54:53.362 align:middle line:90% properties. 00:54:53.362 --> 00:54:55.820 align:middle line:84% That's one way to mention is to say that they are improving 00:54:55.820 --> 00:54:57.278 align:middle line:84% the chemical resistance or chemical 00:54:57.278 --> 00:54:58.695 align:middle line:90% stability of the material. 00:54:58.695 --> 00:55:00.320 align:middle line:84% So when we talk about glass structures, 00:55:00.320 --> 00:55:02.180 align:middle line:84% we say that these rare earth elements, 00:55:02.180 --> 00:55:03.880 align:middle line:84% they have a twofold coordination. 00:55:03.880 --> 00:55:06.060 align:middle line:84% So they help to maintain some network connectivity 00:55:06.060 --> 00:55:07.940 align:middle line:84% and therefore improving the-- reducing 00:55:07.940 --> 00:55:09.280 align:middle line:90% the chemical sensitivity there. 00:55:09.280 --> 00:55:10.988 align:middle line:84% So that's why they added dolomites there. 00:55:10.988 --> 00:55:14.540 align:middle line:84% The sodium sulfates, those are to add the alkaline 00:55:14.540 --> 00:55:18.640 align:middle line:84% to decrease the glass processing temperature. 00:55:18.640 --> 00:55:19.140 align:middle line:90% All right. 00:55:19.140 --> 00:55:23.020 align:middle line:84% So the video shows here-- this is basically talking 00:55:23.020 --> 00:55:25.780 align:middle line:84% about a standard process for making things 00:55:25.780 --> 00:55:27.920 align:middle line:84% like windowpane glasses or architectural glasses. 00:55:27.920 --> 00:55:31.620 align:middle line:84% I want to mention that this float glass process has also 00:55:31.620 --> 00:55:33.090 align:middle line:90% been further advanced. 00:55:33.090 --> 00:55:35.340 align:middle line:84% You can now even actually get high-end glass products, 00:55:35.340 --> 00:55:38.540 align:middle line:84% like consumer electronic products for [? hover glasses ?] 00:55:38.540 --> 00:55:41.300 align:middle line:84% and things like that, also using the float glass process. 00:55:41.300 --> 00:55:43.140 align:middle line:90% So this is actually one example. 00:55:43.140 --> 00:55:45.220 align:middle line:84% This paper basically reports the manufacturing 00:55:45.220 --> 00:55:48.460 align:middle line:84% of ultra-thin glass with a thickness that's 00:55:48.460 --> 00:55:50.920 align:middle line:90% down to about 0.1 millimeters. 00:55:50.920 --> 00:55:53.860 align:middle line:84% That's about a human hair thickness, OK? 00:55:53.860 --> 00:55:57.580 align:middle line:84% And it's a four-meter-wide flat sheet. 00:55:57.580 --> 00:55:59.260 align:middle line:84% So I actually had the opportunity 00:55:59.260 --> 00:56:01.860 align:middle line:90% to visit one of these plants. 00:56:01.860 --> 00:56:06.060 align:middle line:84% And when this glass kind of moves around on the rollers, 00:56:06.060 --> 00:56:08.032 align:middle line:90% you can basically see ripples. 00:56:08.032 --> 00:56:09.240 align:middle line:90% They are essentially flexing. 00:56:09.240 --> 00:56:10.240 align:middle line:90% They are flexible. 00:56:10.240 --> 00:56:11.985 align:middle line:84% So it's quite a remarkable process. 00:56:11.985 --> 00:56:13.860 align:middle line:84% Now, if you look at how they actually did it, 00:56:13.860 --> 00:56:17.220 align:middle line:84% they spent lots of time trying to optimize the temperature 00:56:17.220 --> 00:56:19.900 align:middle line:90% distribution across zones here. 00:56:19.900 --> 00:56:21.740 align:middle line:84% They even spent lots of time optimizing 00:56:21.740 --> 00:56:24.100 align:middle line:84% the location of these rollers on the side 00:56:24.100 --> 00:56:27.260 align:middle line:84% to ensure it generates uniform stretching force rather 00:56:27.260 --> 00:56:31.930 align:middle line:84% than having stress or strain localization. 00:56:31.930 --> 00:56:37.080 align:middle line:84% So in the end, they were able to get glass surface roughness-- 00:56:37.080 --> 00:56:38.740 align:middle line:84% for example, on the top surface-- 00:56:38.740 --> 00:56:41.910 align:middle line:84% down to about 1.5 nanometers [? RMS ?] value, 00:56:41.910 --> 00:56:44.570 align:middle line:90% which is quite remarkable. 00:56:44.570 --> 00:56:47.050 align:middle line:84% This basically just relies on surface tension. 00:56:47.050 --> 00:56:48.782 align:middle line:90% So that's quite good. 00:56:48.782 --> 00:56:50.490 align:middle line:84% Now, the downside, though, is that if you 00:56:50.490 --> 00:56:53.870 align:middle line:84% use this kind of tin bath, on the bottom surface, 00:56:53.870 --> 00:56:57.010 align:middle line:84% you still have the contact of the glass with the tin surface. 00:56:57.010 --> 00:56:59.410 align:middle line:84% This increases the surface roughness up 00:56:59.410 --> 00:57:01.770 align:middle line:90% to about 3 or 4 nanometers. 00:57:01.770 --> 00:57:04.090 align:middle line:84% Also, at the same time, this may cause 00:57:04.090 --> 00:57:05.520 align:middle line:90% a little bit of contamination. 00:57:05.520 --> 00:57:07.770 align:middle line:84% There can be a little bit of diffusion, interdiffusion 00:57:07.770 --> 00:57:09.490 align:middle line:90% between tin and the glass. 00:57:09.490 --> 00:57:11.810 align:middle line:84% Also, any kind of a mechanical vibration 00:57:11.810 --> 00:57:13.970 align:middle line:84% or any kind of surface unevenness of the tin bath 00:57:13.970 --> 00:57:15.930 align:middle line:84% is going to translate into unevenness 00:57:15.930 --> 00:57:19.370 align:middle line:84% of the surface of the glass as well at the bottom surface. 00:57:19.370 --> 00:57:24.890 align:middle line:84% So that's why, if you're looking for very high-end, extremely 00:57:24.890 --> 00:57:28.770 align:middle line:84% high-quality surface glasses, for example, for semiconductor 00:57:28.770 --> 00:57:32.690 align:middle line:84% manufacturing processes, people tend 00:57:32.690 --> 00:57:36.650 align:middle line:84% to use a different manufacturing process. 00:57:36.650 --> 00:57:40.250 align:middle line:84% Where the glass surface is formed without contact 00:57:40.250 --> 00:57:42.970 align:middle line:90% into any substance. 00:57:42.970 --> 00:57:45.450 align:middle line:84% So there's a bunch of these kinds of variants 00:57:45.450 --> 00:57:46.690 align:middle line:90% of this process there. 00:57:46.690 --> 00:57:49.810 align:middle line:84% They are typically called down-draw process. 00:57:49.810 --> 00:57:52.490 align:middle line:84% I'm showing you two variants of this process. 00:57:52.490 --> 00:57:54.850 align:middle line:84% On the left-hand side, this is a process 00:57:54.850 --> 00:57:56.450 align:middle line:84% that's developed by Schott, which 00:57:56.450 --> 00:57:58.190 align:middle line:90% is a German glass manufacturer. 00:57:58.190 --> 00:58:01.370 align:middle line:84% So the way it works is that you have your molten glass, 00:58:01.370 --> 00:58:04.770 align:middle line:84% it comes out from an orifice at the bottom of the furnace, 00:58:04.770 --> 00:58:07.150 align:middle line:84% and then this glass melt essentially just drops. 00:58:07.150 --> 00:58:09.390 align:middle line:84% It comes down by gravitational force. 00:58:09.390 --> 00:58:13.160 align:middle line:90% 00:58:13.160 --> 00:58:15.730 align:middle line:84% And in the process here, this glass surface 00:58:15.730 --> 00:58:18.090 align:middle line:84% is not coming into contact with anything. 00:58:18.090 --> 00:58:20.210 align:middle line:84% So you maintain the pristine glass quality. 00:58:20.210 --> 00:58:22.450 align:middle line:84% And in the end, you then go through annealing furnace 00:58:22.450 --> 00:58:23.450 align:middle line:90% and then go to a roller. 00:58:23.450 --> 00:58:25.410 align:middle line:84% You can get continuous glass ribbon coming out 00:58:25.410 --> 00:58:26.570 align:middle line:90% from the furnace that way. 00:58:26.570 --> 00:58:30.470 align:middle line:84% Now, Corning has its own patented process. 00:58:30.470 --> 00:58:33.102 align:middle line:90% They call it the fusion process. 00:58:33.102 --> 00:58:34.810 align:middle line:84% I'm going to show you a little video that 00:58:34.810 --> 00:58:37.370 align:middle line:90% shows how this is done. 00:58:37.370 --> 00:58:38.310 align:middle line:90% So same idea. 00:58:38.310 --> 00:58:40.790 align:middle line:84% You start by mixing them, put them into a furnace. 00:58:40.790 --> 00:58:45.690 align:middle line:90% 00:58:45.690 --> 00:58:47.098 align:middle line:90% It's also a continuous process. 00:58:47.098 --> 00:58:48.390 align:middle line:90% It can be a continuous process. 00:58:48.390 --> 00:58:50.370 align:middle line:84% So then, you keep on adding these materials 00:58:50.370 --> 00:58:51.730 align:middle line:90% until it overflows. 00:58:51.730 --> 00:58:55.690 align:middle line:90% 00:58:55.690 --> 00:58:59.250 align:middle line:84% So you see that the glass melts comes down from the bottom, 00:58:59.250 --> 00:59:04.308 align:middle line:90% goes into a big crucible. 00:59:04.308 --> 00:59:06.350 align:middle line:84% Then because you continuously add the glass melt, 00:59:06.350 --> 00:59:08.110 align:middle line:84% it starts to overflow from the top. 00:59:08.110 --> 00:59:12.010 align:middle line:84% Then the glass doesn't come out from two sides of the crucible. 00:59:12.010 --> 00:59:14.010 align:middle line:84% You engineer the crucible so that the bottom 00:59:14.010 --> 00:59:15.610 align:middle line:90% has this kind of wedge shape. 00:59:15.610 --> 00:59:18.230 align:middle line:84% So when the liquid comes down, it comes at the bottom, 00:59:18.230 --> 00:59:21.650 align:middle line:84% merges, and forms a thin sheet of glass. 00:59:21.650 --> 00:59:24.110 align:middle line:90% And it cools down as it drops. 00:59:24.110 --> 00:59:27.810 align:middle line:90% 00:59:27.810 --> 00:59:29.890 align:middle line:84% So that's why they call it fusion process-- 00:59:29.890 --> 00:59:33.170 align:middle line:84% because it involves a fusion of two liquid streams at the bottom 00:59:33.170 --> 00:59:35.570 align:middle line:90% of the crucible there. 00:59:35.570 --> 00:59:36.530 align:middle line:90% OK. 00:59:36.530 --> 00:59:37.972 align:middle line:90% So same idea there. 00:59:37.972 --> 00:59:39.930 align:middle line:84% You want to make sure that when you're actually 00:59:39.930 --> 00:59:41.810 align:middle line:84% trying to form the glass surface, 00:59:41.810 --> 00:59:44.477 align:middle line:84% you don't have any contamination or it doesn't come into contact 00:59:44.477 --> 00:59:45.570 align:middle line:90% with any other substances. 00:59:45.570 --> 00:59:49.890 align:middle line:84% So that's why this is mostly used for high-end applications 00:59:49.890 --> 00:59:52.212 align:middle line:84% like flat-panel displays, where you 00:59:52.212 --> 00:59:54.670 align:middle line:84% need to process all kinds of electronic transistors on top. 00:59:54.670 --> 00:59:56.753 align:middle line:84% So it requires extremely high surface quality free 00:59:56.753 --> 00:59:57.810 align:middle line:90% of contamination. 00:59:57.810 --> 00:59:58.570 align:middle line:90% Question. 00:59:58.570 --> 01:00:02.370 align:middle line:84% AUDIENCE: Is-- for the Corning method, 01:00:02.370 --> 01:00:05.490 align:middle line:84% is the crucible hot on the exterior? 01:00:05.490 --> 01:00:09.113 align:middle line:84% Are there binding issues as the two glass faces-- 01:00:09.113 --> 01:00:10.530 align:middle line:84% PROFESSOR: Oh, you mean like-- ah. 01:00:10.530 --> 01:00:11.650 align:middle line:90% OK. 01:00:11.650 --> 01:00:13.210 align:middle line:84% Normally no, because it's actually 01:00:13.210 --> 01:00:14.725 align:middle line:90% at a high enough temperature. 01:00:14.725 --> 01:00:16.350 align:middle line:84% So the glass is basically just a fluid. 01:00:16.350 --> 01:00:19.083 align:middle line:84% So when they come together, it's just basically two fluids 01:00:19.083 --> 01:00:19.750 align:middle line:90% mixing together. 01:00:19.750 --> 01:00:22.510 align:middle line:84% It's not two solid sheets trying to bind together. 01:00:22.510 --> 01:00:24.150 align:middle line:90% Basically, it's a fluid stream. 01:00:24.150 --> 01:00:27.110 align:middle line:84% And it slowly cools down and the viscosity increases. 01:00:27.110 --> 01:00:28.570 align:middle line:84% That's when it becomes solid glass. 01:00:28.570 --> 01:00:28.890 align:middle line:90% OK. 01:00:28.890 --> 01:00:29.390 align:middle line:90% Yes? 01:00:29.390 --> 01:00:31.432 align:middle line:84% AUDIENCE: What is the benefit of that versus just 01:00:31.432 --> 01:00:33.620 align:middle line:90% having a thicker [INAUDIBLE]? 01:00:33.620 --> 01:00:34.745 align:middle line:90% PROFESSOR: Like this one? 01:00:34.745 --> 01:00:35.370 align:middle line:90% AUDIENCE: Yeah. 01:00:35.370 --> 01:00:37.495 align:middle line:84% What is the benefit of the Corning technique there? 01:00:37.495 --> 01:00:39.330 align:middle line:90% PROFESSOR: OK. 01:00:39.330 --> 01:00:40.070 align:middle line:90% Patent. 01:00:40.070 --> 01:00:42.470 align:middle line:90% 01:00:42.470 --> 01:00:42.970 align:middle line:90% Yeah. 01:00:42.970 --> 01:00:44.970 align:middle line:84% Each of the glass company have their own patents 01:00:44.970 --> 01:00:45.750 align:middle line:90% on the process. 01:00:45.750 --> 01:00:47.928 align:middle line:84% Schott holds patent on this process, 01:00:47.928 --> 01:00:49.470 align:middle line:84% Corning holds patent on that process. 01:00:49.470 --> 01:00:51.870 align:middle line:84% They cannot use the other people's process. 01:00:51.870 --> 01:00:54.210 align:middle line:84% So that's why they develop their own variants 01:00:54.210 --> 01:00:55.762 align:middle line:90% of the down-draw process. 01:00:55.762 --> 01:00:57.470 align:middle line:84% I mean, that's the main reason, honestly. 01:00:57.470 --> 01:00:59.070 align:middle line:84% I don't see a big difference, to be honest, 01:00:59.070 --> 01:01:00.710 align:middle line:84% between the fusion process and the down-drawn process. 01:01:00.710 --> 01:01:02.002 align:middle line:90% They are more or less the same. 01:01:02.002 --> 01:01:04.170 align:middle line:84% If you look at other glass manufacturers, AGC 01:01:04.170 --> 01:01:06.730 align:middle line:84% in Japan, Pilkington in the UK, they also 01:01:06.730 --> 01:01:09.490 align:middle line:84% have their own variants of this kind of down-draw process. 01:01:09.490 --> 01:01:11.573 align:middle line:84% AUDIENCE: I'm going to create the up-draw process. 01:01:11.573 --> 01:01:12.442 align:middle line:90% [LAUGHTER] 01:01:12.442 --> 01:01:14.150 align:middle line:84% PROFESSOR: You are going against gravity. 01:01:14.150 --> 01:01:16.390 align:middle line:84% You can patent it, but you are going against gravity. 01:01:16.390 --> 01:01:18.010 align:middle line:90% That's the downside there. 01:01:18.010 --> 01:01:19.070 align:middle line:90% This is a little easier. 01:01:19.070 --> 01:01:20.010 align:middle line:90% You just let things flow. 01:01:20.010 --> 01:01:21.110 align:middle line:84% AUDIENCE: I can corner the market. 01:01:21.110 --> 01:01:21.610 align:middle line:90% So. 01:01:21.610 --> 01:01:23.790 align:middle line:84% PROFESSOR: You could do a horizontal draw maybe. 01:01:23.790 --> 01:01:29.450 align:middle line:84% [LAUGHS] Oh, by the way, do you know when this process was 01:01:29.450 --> 01:01:31.290 align:middle line:90% first developed? 01:01:31.290 --> 01:01:33.420 align:middle line:84% AUDIENCE: Like any sort of down-draw method? 01:01:33.420 --> 01:01:34.087 align:middle line:90% PROFESSOR: Yeah. 01:01:34.087 --> 01:01:38.760 align:middle line:90% 01:01:38.760 --> 01:01:39.740 align:middle line:90% When, I mean. 01:01:39.740 --> 01:01:42.960 align:middle line:90% When was it-- yeah. 01:01:42.960 --> 01:01:44.540 align:middle line:90% AUDIENCE: Recently? 01:01:44.540 --> 01:01:47.040 align:middle line:84% PROFESSOR: I mean, the demand really only comes in recently. 01:01:47.040 --> 01:01:49.640 align:middle line:84% It's basically when all the consumer electronics companies 01:01:49.640 --> 01:01:52.580 align:middle line:84% started to want to make this kind of high-quality glasses, 01:01:52.580 --> 01:01:54.480 align:middle line:84% that's actually when the market matures. 01:01:54.480 --> 01:01:57.440 align:middle line:84% It was developed back in the 1960s. 01:01:57.440 --> 01:01:58.800 align:middle line:90% Yeah. 01:01:58.800 --> 01:02:00.680 align:middle line:84% So people at the time, they were thinking 01:02:00.680 --> 01:02:02.880 align:middle line:84% that they need a high-end glass process to make 01:02:02.880 --> 01:02:05.640 align:middle line:90% the windshields for cars. 01:02:05.640 --> 01:02:06.940 align:middle line:90% The market doesn't exist. 01:02:06.940 --> 01:02:09.600 align:middle line:84% Nobody needs these high-end glasses with a very high 01:02:09.600 --> 01:02:11.080 align:middle line:90% precision surface quality. 01:02:11.080 --> 01:02:14.033 align:middle line:84% So Corning actually goes back to their dossier, right, 01:02:14.033 --> 01:02:15.200 align:middle line:90% looking into old literature. 01:02:15.200 --> 01:02:15.700 align:middle line:90% When? 01:02:15.700 --> 01:02:18.880 align:middle line:84% Like 20 years ago when Apple was approaching them trying 01:02:18.880 --> 01:02:20.460 align:middle line:90% to make iPhone cover glasses. 01:02:20.460 --> 01:02:22.480 align:middle line:84% They actually had to go back into their dossier, 01:02:22.480 --> 01:02:26.080 align:middle line:84% dig out this old process and kind of scale it up 01:02:26.080 --> 01:02:27.260 align:middle line:90% to actually manufacturing. 01:02:27.260 --> 01:02:29.340 align:middle line:84% So yeah, I mean, it's an old process, 01:02:29.340 --> 01:02:31.840 align:middle line:84% but it has a renewed interest now because of the electronics 01:02:31.840 --> 01:02:32.460 align:middle line:90% industry. 01:02:32.460 --> 01:02:35.640 align:middle line:90% 01:02:35.640 --> 01:02:36.800 align:middle line:90% OK. 01:02:36.800 --> 01:02:40.280 align:middle line:90% How do I go to the next slide? 01:02:40.280 --> 01:02:41.920 align:middle line:90% Oh, all right. 01:02:41.920 --> 01:02:45.860 align:middle line:84% So far we've been talking about how to make flat-panel glasses. 01:02:45.860 --> 01:02:47.010 align:middle line:90% Big, flat glasses, right? 01:02:47.010 --> 01:02:48.760 align:middle line:84% So next, I'm going to talk about something 01:02:48.760 --> 01:02:50.010 align:middle line:90% that's a little bit different. 01:02:50.010 --> 01:02:53.560 align:middle line:84% It's glassblowing-- using air to help to conform glasses 01:02:53.560 --> 01:02:54.800 align:middle line:90% into different shapes. 01:02:54.800 --> 01:02:57.420 align:middle line:84% There are a few different variants of glassblowing here. 01:02:57.420 --> 01:03:00.440 align:middle line:84% In this slide, I'm showing you the manual version, 01:03:00.440 --> 01:03:03.050 align:middle line:84% where this is what people do in a glass workshop. 01:03:03.050 --> 01:03:05.300 align:middle line:84% This is what you're going to see in the MIT Glass Lab. 01:03:05.300 --> 01:03:06.800 align:middle line:84% We're going to try to make pumpkins, 01:03:06.800 --> 01:03:09.060 align:middle line:84% for example, that involves the glassblowing process. 01:03:09.060 --> 01:03:13.120 align:middle line:84% So in the glassblowing process, you basically 01:03:13.120 --> 01:03:16.540 align:middle line:84% have this big blow pipe, which is hollow in the middle, 01:03:16.540 --> 01:03:19.000 align:middle line:90% so you can blow air through it. 01:03:19.000 --> 01:03:23.940 align:middle line:84% You then collect a big gob of glass. 01:03:23.940 --> 01:03:25.080 align:middle line:90% Big chunk of glass. 01:03:25.080 --> 01:03:27.920 align:middle line:90% They call it big "gob" of glass. 01:03:27.920 --> 01:03:30.800 align:middle line:84% You start to see these specific terms that people use 01:03:30.800 --> 01:03:33.760 align:middle line:90% when it comes to glassmaking. 01:03:33.760 --> 01:03:36.880 align:middle line:84% This big gob of glass, then you collect it 01:03:36.880 --> 01:03:39.320 align:middle line:90% at the end of the blowpipe. 01:03:39.320 --> 01:03:42.400 align:middle line:84% You can blow air bubble into it, and you essentially 01:03:42.400 --> 01:03:45.360 align:middle line:84% push it against the mold as you blow air into it. 01:03:45.360 --> 01:03:47.840 align:middle line:84% So then the outer surface of the gob 01:03:47.840 --> 01:03:50.280 align:middle line:84% then conforms to the shape of the mold. 01:03:50.280 --> 01:03:54.720 align:middle line:84% And this kind of structure is essentially a specific shape, 01:03:54.720 --> 01:03:57.200 align:middle line:84% and the air bubble in it is called a parison. 01:03:57.200 --> 01:04:00.700 align:middle line:90% 01:04:00.700 --> 01:04:02.460 align:middle line:90% Sort of like pre-formed glass. 01:04:02.460 --> 01:04:05.720 align:middle line:84% But that's the name people use to call this kind of thing. 01:04:05.720 --> 01:04:08.900 align:middle line:84% And then you can then open it up, 01:04:08.900 --> 01:04:11.260 align:middle line:84% or you can take it to different kinds of geometries. 01:04:11.260 --> 01:04:12.635 align:middle line:84% There are a ton of different ways 01:04:12.635 --> 01:04:15.200 align:middle line:84% people can modify this process to create all kinds 01:04:15.200 --> 01:04:16.600 align:middle line:90% of delicate glass products. 01:04:16.600 --> 01:04:18.200 align:middle line:84% You're going to see that at the MIT Glass Lab. 01:04:18.200 --> 01:04:19.658 align:middle line:84% It's a lot easier for you to see it 01:04:19.658 --> 01:04:22.760 align:middle line:84% than for me trying to explain it, what happens. 01:04:22.760 --> 01:04:25.080 align:middle line:84% The person that actually does the blowing job 01:04:25.080 --> 01:04:27.207 align:middle line:90% is called a gaffer. 01:04:27.207 --> 01:04:29.540 align:middle line:84% Depending on context, if you go to different industries, 01:04:29.540 --> 01:04:31.000 align:middle line:90% "gaffer" means different things. 01:04:31.000 --> 01:04:32.880 align:middle line:84% If you go to a movie industry, "gaffer" 01:04:32.880 --> 01:04:34.800 align:middle line:84% is the person in charge of lighting. 01:04:34.800 --> 01:04:37.200 align:middle line:84% If you go to a sports team, "gaffer" 01:04:37.200 --> 01:04:39.320 align:middle line:90% means the manager of the club. 01:04:39.320 --> 01:04:41.960 align:middle line:84% If you go to glass, "gaffer" is the person actually in charge 01:04:41.960 --> 01:04:42.700 align:middle line:90% of glassblowing. 01:04:42.700 --> 01:04:44.120 align:middle line:90% So it's basically like the boss. 01:04:44.120 --> 01:04:44.880 align:middle line:90% OK? 01:04:44.880 --> 01:04:48.440 align:middle line:84% So now, this job for gaffer, or glass worker, 01:04:48.440 --> 01:04:50.483 align:middle line:84% it's very much a technical know-how 01:04:50.483 --> 01:04:52.400 align:middle line:84% that's usually passed down from one generation 01:04:52.400 --> 01:04:53.860 align:middle line:90% to another of glass makers. 01:04:53.860 --> 01:04:56.660 align:middle line:84% You don't learn it from a textbook. 01:04:56.660 --> 01:04:58.360 align:middle line:84% You learn it by actually doing it. 01:04:58.360 --> 01:05:03.120 align:middle line:84% And even up till today, there's still demand, 01:05:03.120 --> 01:05:06.500 align:middle line:84% a lot of demand into making specialized glass products. 01:05:06.500 --> 01:05:08.480 align:middle line:84% These are some scientific instruments 01:05:08.480 --> 01:05:11.440 align:middle line:84% that people make using this kind of glassblowing process. 01:05:11.440 --> 01:05:13.620 align:middle line:84% And you just cannot simply buy it. 01:05:13.620 --> 01:05:15.340 align:middle line:84% This is not off-the-shelf products. 01:05:15.340 --> 01:05:18.440 align:middle line:84% You need to have a good glass blower that can actually create 01:05:18.440 --> 01:05:19.940 align:middle line:90% these kinds of things for you. 01:05:19.940 --> 01:05:23.117 align:middle line:90% So it's a very skill. 01:05:23.117 --> 01:05:24.200 align:middle line:90% It requires lots of skill. 01:05:24.200 --> 01:05:26.760 align:middle line:84% It's a job that requires a lot of skill and experience 01:05:26.760 --> 01:05:28.280 align:middle line:90% to design the process. 01:05:28.280 --> 01:05:29.880 align:middle line:90% OK. 01:05:29.880 --> 01:05:30.520 align:middle line:90% OK. 01:05:30.520 --> 01:05:33.800 align:middle line:84% So this is the more manual process here. 01:05:33.800 --> 01:05:35.760 align:middle line:84% Now, at the industrial scale, people also 01:05:35.760 --> 01:05:38.200 align:middle line:84% use a similar blowing process to create, 01:05:38.200 --> 01:05:40.520 align:middle line:90% in this case, glass containers. 01:05:40.520 --> 01:05:42.985 align:middle line:84% So what I'm showing you here, top and bottom, these 01:05:42.985 --> 01:05:44.360 align:middle line:84% are two kinds of glass containers 01:05:44.360 --> 01:05:46.560 align:middle line:84% that are created using this similar process here. 01:05:46.560 --> 01:05:49.320 align:middle line:84% On top, this is for narrow-neck containers-- 01:05:49.320 --> 01:05:52.140 align:middle line:90% like beverage bottles. 01:05:52.140 --> 01:05:56.360 align:middle line:84% So for beverage bottle, you do a so-called blow-and-blow process. 01:05:56.360 --> 01:05:59.960 align:middle line:84% So what you do, you start from a gob of glass. 01:05:59.960 --> 01:06:02.740 align:middle line:90% You put it into a mold. 01:06:02.740 --> 01:06:05.720 align:middle line:84% You have an opening at one end where you use compressed air 01:06:05.720 --> 01:06:07.480 align:middle line:90% to blow this mold. 01:06:07.480 --> 01:06:11.360 align:middle line:84% And then it's going to conform to this closed mold here. 01:06:11.360 --> 01:06:14.400 align:middle line:90% Then you get this parison. 01:06:14.400 --> 01:06:17.200 align:middle line:84% You then put this parison into a second mold, 01:06:17.200 --> 01:06:21.240 align:middle line:84% you blow compressed air again to go to final geometry. 01:06:21.240 --> 01:06:23.120 align:middle line:84% Now, you may wonder, why bother doing 01:06:23.120 --> 01:06:24.380 align:middle line:90% this two-step blowing process? 01:06:24.380 --> 01:06:26.520 align:middle line:84% Why not just simply using one-step blowing? 01:06:26.520 --> 01:06:29.160 align:middle line:84% The reason for that is a couple of things. 01:06:29.160 --> 01:06:31.160 align:middle line:84% One is that people want to minimize 01:06:31.160 --> 01:06:33.400 align:middle line:84% any kind of very large local shear strain, 01:06:33.400 --> 01:06:36.680 align:middle line:84% because those can cause strain accumulation 01:06:36.680 --> 01:06:39.120 align:middle line:84% and maybe leading to cracking of the products. 01:06:39.120 --> 01:06:41.540 align:middle line:84% So by designing this two-step process, 01:06:41.540 --> 01:06:45.760 align:middle line:84% they can separate the engineer, the deformation 01:06:45.760 --> 01:06:47.240 align:middle line:90% in the two blowing steps there. 01:06:47.240 --> 01:06:49.603 align:middle line:84% And this minimizes local strain accumulation. 01:06:49.603 --> 01:06:50.520 align:middle line:90% Makes it more uniform. 01:06:50.520 --> 01:06:54.880 align:middle line:84% Makes the deformation more uniform, basically. 01:06:54.880 --> 01:06:56.920 align:middle line:84% Now, the other thing also to consider here 01:06:56.920 --> 01:06:59.000 align:middle line:84% is that this blowing process takes place 01:06:59.000 --> 01:07:01.520 align:middle line:84% at fairly high temperature, where glass is actually liquid, 01:07:01.520 --> 01:07:02.020 align:middle line:90% right? 01:07:02.020 --> 01:07:06.520 align:middle line:84% It also involves quite a bit of friction between this glass gob 01:07:06.520 --> 01:07:09.000 align:middle line:90% and the mold you're using there. 01:07:09.000 --> 01:07:11.400 align:middle line:84% So this friction is harmful because it leads 01:07:11.400 --> 01:07:13.400 align:middle line:90% to wear and tear of the mold. 01:07:13.400 --> 01:07:15.360 align:middle line:84% So in order to ensure longevity, you 01:07:15.360 --> 01:07:19.520 align:middle line:84% want to make sure that this glass deformation takes 01:07:19.520 --> 01:07:22.540 align:middle line:84% place ideally along the surface normal direction of the mold. 01:07:22.540 --> 01:07:24.710 align:middle line:84% You try to avoid any kind of shear motion 01:07:24.710 --> 01:07:26.910 align:middle line:90% on the surface of the mold. 01:07:26.910 --> 01:07:30.650 align:middle line:84% So having a two-step process also helps with that. 01:07:30.650 --> 01:07:32.190 align:middle line:84% It gives you more degree of freedom 01:07:32.190 --> 01:07:35.790 align:middle line:84% to engineer the process to minimize any kind of wear 01:07:35.790 --> 01:07:38.870 align:middle line:84% and tear due to the shearing motion between the glass gob 01:07:38.870 --> 01:07:41.590 align:middle line:84% and the glass parison and the mold. 01:07:41.590 --> 01:07:45.550 align:middle line:84% Now, at the bottom here, this is for wide-open jars, 01:07:45.550 --> 01:07:48.030 align:middle line:84% like [? Mark's. ?] And this is done 01:07:48.030 --> 01:07:50.170 align:middle line:84% using a so-called press-and-blow process. 01:07:50.170 --> 01:07:51.130 align:middle line:90% It's quite similar. 01:07:51.130 --> 01:07:53.690 align:middle line:84% You replace the first compressed air blowing process 01:07:53.690 --> 01:07:55.210 align:middle line:90% with just a mechanical mold. 01:07:55.210 --> 01:07:57.710 align:middle line:84% You use a mechanical press to essentially form 01:07:57.710 --> 01:08:01.270 align:middle line:84% the parison shape rather than using a blowing process. 01:08:01.270 --> 01:08:02.430 align:middle line:90% OK. 01:08:02.430 --> 01:08:02.950 align:middle line:90% OK. 01:08:02.950 --> 01:08:06.590 align:middle line:84% So what I will do next is I will again 01:08:06.590 --> 01:08:09.230 align:middle line:84% show you another video that actually illustrates 01:08:09.230 --> 01:08:10.770 align:middle line:90% this glassblowing process. 01:08:10.770 --> 01:08:13.150 align:middle line:90% Hopefully no ad this time. 01:08:13.150 --> 01:08:14.670 align:middle line:90% [VIDEO PLAYBACK] 01:08:14.670 --> 01:08:15.970 align:middle line:90% - Why choose glass? 01:08:15.970 --> 01:08:19.189 align:middle line:90% 01:08:19.189 --> 01:08:22.109 align:middle line:84% The benefits of glass [INAUDIBLE]. 01:08:22.109 --> 01:08:24.270 align:middle line:90% It is sustainable. 01:08:24.270 --> 01:08:26.710 align:middle line:90% It is virtually inert. 01:08:26.710 --> 01:08:32.870 align:middle line:84% It is 100% recyclable, reusable, and refillable. 01:08:32.870 --> 01:08:35.270 align:middle line:84% It is safe to store food and drinks in it, 01:08:35.270 --> 01:08:39.670 align:middle line:84% and it is a premium way to market your products. 01:08:39.670 --> 01:08:43.710 align:middle line:84% Glass containers do not contain phthalates, or biphenyl-A, 01:08:43.710 --> 01:08:47.229 align:middle line:84% or any other potential hormone disruptors or carcinogens. 01:08:47.229 --> 01:08:50.189 align:middle line:84% It offers long shelf life as high levels of vacuum 01:08:50.189 --> 01:08:52.510 align:middle line:84% and carbonization can be maintained, 01:08:52.510 --> 01:08:55.069 align:middle line:84% and it can protect the product from the harmful effects 01:08:55.069 --> 01:08:56.590 align:middle line:90% of light. 01:08:56.590 --> 01:08:58.390 align:middle line:90% Manufacturing process. 01:08:58.390 --> 01:09:00.390 align:middle line:90% Where do we start? 01:09:00.390 --> 01:09:03.870 align:middle line:90% Stage one, raw materials. 01:09:03.870 --> 01:09:07.350 align:middle line:84% The major raw materials used in glass container production-- 01:09:07.350 --> 01:09:09.430 align:middle line:84% PROFESSOR: The same as the flat glass. 01:09:09.430 --> 01:09:10.870 align:middle line:90% Mixing different elements. 01:09:10.870 --> 01:09:12.043 align:middle line:90% - --limestone. 01:09:12.043 --> 01:09:13.210 align:middle line:90% PROFESSOR: Batching process. 01:09:13.210 --> 01:09:14.543 align:middle line:90% This is called batching process. 01:09:14.543 --> 01:09:16.510 align:middle line:84% You mix different elements together. 01:09:16.510 --> 01:09:17.029 align:middle line:90% - --cullet. 01:09:17.029 --> 01:09:19.229 align:middle line:84% Cullet is recycled glass that helps 01:09:19.229 --> 01:09:21.670 align:middle line:84% to reduce the amount of raw materials needed 01:09:21.670 --> 01:09:23.350 align:middle line:90% to make new glass. 01:09:23.350 --> 01:09:25.830 align:middle line:84% Cullet provides an important energy savings 01:09:25.830 --> 01:09:27.590 align:middle line:84% by lowering the temperature required 01:09:27.590 --> 01:09:30.790 align:middle line:84% for the melting process, helping to reduce greenhouse gas 01:09:30.790 --> 01:09:32.550 align:middle line:90% emissions. 01:09:32.550 --> 01:09:35.189 align:middle line:90% Stage two, batching. 01:09:35.189 --> 01:09:39.149 align:middle line:84% One, raw materials are delivered into the batch house, 01:09:39.149 --> 01:09:40.790 align:middle line:84% where they are visually inspected 01:09:40.790 --> 01:09:44.750 align:middle line:90% prior to being stored in silos. 01:09:44.750 --> 01:09:49.510 align:middle line:84% Two, it is then weighed and mixed to produce batch. 01:09:49.510 --> 01:09:52.290 align:middle line:84% Three, the batch is then delivered and stored 01:09:52.290 --> 01:09:56.590 align:middle line:84% at the furnace, where it is melted to form glass. 01:09:56.590 --> 01:09:58.810 align:middle line:90% Stage three, melting. 01:09:58.810 --> 01:10:02.510 align:middle line:90% 01:10:02.510 --> 01:10:06.070 align:middle line:84% The batch is continuously fed into one end of the furnace 01:10:06.070 --> 01:10:08.630 align:middle line:90% via a batch charger. 01:10:08.630 --> 01:10:11.990 align:middle line:84% A combustible mixture of natural gas and air is forced 01:10:11.990 --> 01:10:15.310 align:middle line:84% into the furnace to generate a temperature of approximately 01:10:15.310 --> 01:10:20.190 align:middle line:90% 1,565 degrees Celsius. 01:10:20.190 --> 01:10:23.170 align:middle line:84% It is here that the batch is melted to produce glass. 01:10:23.170 --> 01:10:29.870 align:middle line:90% 01:10:29.870 --> 01:10:31.850 align:middle line:90% Stage four, feeders. 01:10:31.850 --> 01:10:34.990 align:middle line:90% 01:10:34.990 --> 01:10:37.270 align:middle line:84% At the end of the forearm, the glass 01:10:37.270 --> 01:10:38.830 align:middle line:84% is then forced through an opening 01:10:38.830 --> 01:10:41.970 align:middle line:84% in the bottom of the spout called an orifice ring. 01:10:41.970 --> 01:10:46.797 align:middle line:84% The glass is then cut by blades called shears. 01:10:46.797 --> 01:10:49.130 align:middle line:84% PROFESSOR: Those are [INAUDIBLE] the technologies that-- 01:10:49.130 --> 01:10:53.430 align:middle line:84% - --elongated cylinders of glass called gobs. 01:10:53.430 --> 01:10:55.750 align:middle line:84% Each gob has the correct amount of glass 01:10:55.750 --> 01:10:57.270 align:middle line:90% to produce one container. 01:10:57.270 --> 01:11:02.430 align:middle line:84% At this stage, they are ready to be formed into glass containers 01:11:02.430 --> 01:11:04.570 align:middle line:84% and are delivered to the forming machine. 01:11:04.570 --> 01:11:07.110 align:middle line:90% 01:11:07.110 --> 01:11:09.750 align:middle line:90% Stage five, forming. 01:11:09.750 --> 01:11:12.070 align:middle line:84% The forming machine uses compressed air 01:11:12.070 --> 01:11:14.110 align:middle line:84% to transform the gobs into containers 01:11:14.110 --> 01:11:16.230 align:middle line:90% in a two-step process. 01:11:16.230 --> 01:11:19.270 align:middle line:84% The gob is delivered to the blank side of the machine, where 01:11:19.270 --> 01:11:21.190 align:middle line:84% it is formed into a parison, which 01:11:21.190 --> 01:11:22.970 align:middle line:90% is a blank form of a container. 01:11:22.970 --> 01:11:24.990 align:middle line:84% It is then transferred onto the mold side 01:11:24.990 --> 01:11:27.110 align:middle line:84% of the machine, where it is blown 01:11:27.110 --> 01:11:29.170 align:middle line:84% into the final shape of the container. 01:11:29.170 --> 01:11:32.430 align:middle line:90% 01:11:32.430 --> 01:11:35.790 align:middle line:90% Stage six, hot end coating. 01:11:35.790 --> 01:11:39.270 align:middle line:90% Tin coating. 01:11:39.270 --> 01:11:42.830 align:middle line:84% Once formed, the containers are sent through a hot end coating 01:11:42.830 --> 01:11:45.670 align:middle line:84% hood and are covered with a thin layer of tin. 01:11:45.670 --> 01:11:49.310 align:middle line:84% This is part one of a permanent coating process. 01:11:49.310 --> 01:11:51.410 align:middle line:90% Stage seven, annealing. 01:11:51.410 --> 01:11:54.870 align:middle line:90% 01:11:54.870 --> 01:11:57.230 align:middle line:84% When a new glass container is formed, 01:11:57.230 --> 01:12:01.190 align:middle line:84% the outside surface cools more rapidly than the inside surface, 01:12:01.190 --> 01:12:03.050 align:middle line:90% causing stresses in the glass. 01:12:03.050 --> 01:12:06.070 align:middle line:84% The process to relieve these stresses is called anneal 01:12:06.070 --> 01:12:08.150 align:middle line:90% and is done in a lehr. 01:12:08.150 --> 01:12:12.070 align:middle line:84% The lehr reheats the containers and gradually and evenly cools 01:12:12.070 --> 01:12:13.530 align:middle line:90% them to room temperature. 01:12:13.530 --> 01:12:15.790 align:middle line:84% The time taken to travel through the lehr 01:12:15.790 --> 01:12:18.420 align:middle line:84% depends on the container, which, on average, is 01:12:18.420 --> 01:12:21.620 align:middle line:90% between 60 and 80 minutes. 01:12:21.620 --> 01:12:24.660 align:middle line:90% Stage eight, hold and spray. 01:12:24.660 --> 01:12:27.620 align:middle line:90% Duracote. 01:12:27.620 --> 01:12:30.100 align:middle line:84% At this stage, a thin layer of polymer 01:12:30.100 --> 01:12:32.340 align:middle line:84% is applied to the container to provide them 01:12:32.340 --> 01:12:35.780 align:middle line:84% with a scratch-resistant coating. 01:12:35.780 --> 01:12:38.020 align:middle line:84% This coating will also allow the containers 01:12:38.020 --> 01:12:42.380 align:middle line:84% to travel along the customer's filling line without jamming up. 01:12:42.380 --> 01:12:44.920 align:middle line:84% PROFESSOR: It's like a lubricant, reduce the friction. 01:12:44.920 --> 01:12:47.380 align:middle line:90% - --Inspection. 01:12:47.380 --> 01:12:49.940 align:middle line:84% Before packaging, each glass container 01:12:49.940 --> 01:12:52.380 align:middle line:84% undergoes a rigorous inspection process 01:12:52.380 --> 01:12:54.540 align:middle line:90% to ensure the highest quality. 01:12:54.540 --> 01:12:57.020 align:middle line:84% It is inspected at multiple stages of the production 01:12:57.020 --> 01:12:58.060 align:middle line:90% process. 01:12:58.060 --> 01:13:02.340 align:middle line:84% Bottles that do not meet OIPJC's stringent design specifications 01:13:02.340 --> 01:13:08.140 align:middle line:84% are rejected and recycled as cullet. 01:13:08.140 --> 01:13:10.420 align:middle line:84% Finished containers are prepared for shipment 01:13:10.420 --> 01:13:12.140 align:middle line:90% by our packaging department. 01:13:12.140 --> 01:13:14.060 align:middle line:84% From our warehouses, our products 01:13:14.060 --> 01:13:17.276 align:middle line:84% are shipped all over Southeast Asia. 01:13:17.276 --> 01:13:19.045 align:middle line:90% [END PLAYBACK] 01:13:19.045 --> 01:13:19.920 align:middle line:90% PROFESSOR: All right. 01:13:19.920 --> 01:13:21.628 align:middle line:84% So there are a few things that's actually 01:13:21.628 --> 01:13:25.820 align:middle line:84% mentioned there in this process that I just want to highlight. 01:13:25.820 --> 01:13:27.800 align:middle line:84% One is that they talk about this tin coating. 01:13:27.800 --> 01:13:30.740 align:middle line:84% So the reason they do a tin coating-- 01:13:30.740 --> 01:13:32.100 align:middle line:90% there are two purposes there. 01:13:32.100 --> 01:13:36.960 align:middle line:84% One is that the tin oxide, when the glass contains tin oxide, 01:13:36.960 --> 01:13:39.332 align:middle line:84% it has a higher hardness compared to normal glass. 01:13:39.332 --> 01:13:41.540 align:middle line:84% And higher hardness is really important in preventing 01:13:41.540 --> 01:13:43.152 align:middle line:90% any kind of scratch damage. 01:13:43.152 --> 01:13:45.360 align:middle line:84% So later on when we talk about mechanical properties, 01:13:45.360 --> 01:13:47.620 align:middle line:84% you're going to find that the Achilles heel of glass 01:13:47.620 --> 01:13:48.995 align:middle line:84% in terms of mechanical properties 01:13:48.995 --> 01:13:50.225 align:middle line:90% is usually surface defects. 01:13:50.225 --> 01:13:51.600 align:middle line:84% If there are any surface defects, 01:13:51.600 --> 01:13:52.683 align:middle line:90% they become the weak link. 01:13:52.683 --> 01:13:55.060 align:middle line:84% You can have cracks initiate and propagate quickly 01:13:55.060 --> 01:13:56.160 align:middle line:90% from those defects. 01:13:56.160 --> 01:14:00.540 align:middle line:84% So that's why having a surface treatment to empower glass 01:14:00.540 --> 01:14:02.720 align:middle line:84% with a higher scratch resistance is quite important. 01:14:02.720 --> 01:14:04.095 align:middle line:84% That's why they do a tin coating. 01:14:04.095 --> 01:14:05.660 align:middle line:90% One purpose. 01:14:05.660 --> 01:14:08.760 align:middle line:84% Now, second purpose is that if you think about glass, 01:14:08.760 --> 01:14:11.640 align:middle line:84% its surface is-- if it's not treated, it's hydrophilic. 01:14:11.640 --> 01:14:15.140 align:middle line:84% That's why you see, during rain, raindrops 01:14:15.140 --> 01:14:17.180 align:middle line:90% can hang on glass windows. 01:14:17.180 --> 01:14:20.873 align:middle line:84% But after you have done the hot end coding, 01:14:20.873 --> 01:14:22.540 align:middle line:84% we're trying to do the cold end coating. 01:14:22.540 --> 01:14:24.140 align:middle line:84% That's a polymer coating, duracote, 01:14:24.140 --> 01:14:28.940 align:middle line:84% to reduce friction and also further improve 01:14:28.940 --> 01:14:30.180 align:middle line:90% scratch resistance. 01:14:30.180 --> 01:14:33.740 align:middle line:84% So the polymer coating is hydrophobic, 01:14:33.740 --> 01:14:37.020 align:middle line:84% so it doesn't stick very well to the glass surface. 01:14:37.020 --> 01:14:39.140 align:middle line:84% So by adding tin there, tin actually 01:14:39.140 --> 01:14:41.540 align:middle line:84% renders a more hydrophobic surface, 01:14:41.540 --> 01:14:45.220 align:middle line:84% which helps improve adhesion between the subsequent polymer 01:14:45.220 --> 01:14:46.900 align:middle line:90% coating with the glass surface. 01:14:46.900 --> 01:14:50.020 align:middle line:84% So that's why, actually, people do this tin coating there, 01:14:50.020 --> 01:14:51.460 align:middle line:90% just to serve their purpose. 01:14:51.460 --> 01:14:53.340 align:middle line:90% OK? 01:14:53.340 --> 01:14:53.840 align:middle line:90% Yes? 01:14:53.840 --> 01:14:55.820 align:middle line:84% AUDIENCE: Do they have to remove the coating 01:14:55.820 --> 01:14:57.600 align:middle line:90% when they recycle the glass? 01:14:57.600 --> 01:15:00.740 align:middle line:90% Or do you just get-- 01:15:00.740 --> 01:15:05.180 align:middle line:84% or maybe that concentration of tin becomes negligible? 01:15:05.180 --> 01:15:07.335 align:middle line:90% PROFESSOR: Great question. 01:15:07.335 --> 01:15:08.960 align:middle line:84% There are actually two coatings, right? 01:15:08.960 --> 01:15:11.380 align:middle line:90% There's also-- well, it depends. 01:15:11.380 --> 01:15:13.140 align:middle line:84% When you recycle glass products, there 01:15:13.140 --> 01:15:14.860 align:middle line:84% is a thin layer of polymer coatings. 01:15:14.860 --> 01:15:17.980 align:middle line:84% Those things just burn away in the glass furnace. 01:15:17.980 --> 01:15:19.220 align:middle line:90% Becomes carbon dioxide. 01:15:19.220 --> 01:15:21.480 align:middle line:84% The tin, because it's only on the surface, 01:15:21.480 --> 01:15:23.660 align:middle line:84% it's a very, very small amount, so it barely 01:15:23.660 --> 01:15:24.640 align:middle line:90% impacts the process. 01:15:24.640 --> 01:15:26.500 align:middle line:84% So that's why they can go back immediately. 01:15:26.500 --> 01:15:28.083 align:middle line:84% It's only a very thin layer of coating 01:15:28.083 --> 01:15:30.720 align:middle line:84% there, like a few hundred nanometers. 01:15:30.720 --> 01:15:34.340 align:middle line:84% So if you look at the actual fraction, it's negligible. 01:15:34.340 --> 01:15:34.940 align:middle line:90% Yes? 01:15:34.940 --> 01:15:37.440 align:middle line:84% AUDIENCE: Is it possible-- so I mean, 01:15:37.440 --> 01:15:40.180 align:middle line:84% I guess the primary way that they kind of recycle glass 01:15:40.180 --> 01:15:42.260 align:middle line:84% is by using it as cullet, which is basically, 01:15:42.260 --> 01:15:44.500 align:middle line:90% like, 30% of the [INAUDIBLE]. 01:15:44.500 --> 01:15:49.940 align:middle line:84% So is it not possible to do the full recycling of all produced 01:15:49.940 --> 01:15:50.660 align:middle line:90% glassware? 01:15:50.660 --> 01:15:51.700 align:middle line:90% PROFESSOR: You could. 01:15:51.700 --> 01:15:52.220 align:middle line:90% Yeah. 01:15:52.220 --> 01:15:54.318 align:middle line:84% If you have enough stream, a stable supply stream 01:15:54.318 --> 01:15:55.860 align:middle line:84% of weight glasses, then in principle, 01:15:55.860 --> 01:15:56.800 align:middle line:90% yeah, you can do that. 01:15:56.800 --> 01:15:57.300 align:middle line:90% Yeah. 01:15:57.300 --> 01:15:59.880 align:middle line:84% Yeah, it's a supply chain problem. 01:15:59.880 --> 01:16:01.480 align:middle line:84% It's not about the technology problem. 01:16:01.480 --> 01:16:01.700 align:middle line:90% Yeah. 01:16:01.700 --> 01:16:03.325 align:middle line:84% And that's one advantage about glasses. 01:16:03.325 --> 01:16:06.220 align:middle line:84% Glasses, in principle, they are fully recyclable, 01:16:06.220 --> 01:16:10.120 align:middle line:90% unlike other kind of products. 01:16:10.120 --> 01:16:11.922 align:middle line:84% The glass industry is very power-hungry 01:16:11.922 --> 01:16:14.380 align:middle line:84% because it takes lots of energy to actually melt the glass. 01:16:14.380 --> 01:16:16.060 align:middle line:84% So being able to recycle is quite 01:16:16.060 --> 01:16:18.940 align:middle line:84% important in reducing carbon footprint of the industry. 01:16:18.940 --> 01:16:19.578 align:middle line:90% Yeah. 01:16:19.578 --> 01:16:21.620 align:middle line:84% Now, the second thing I also want to mention here 01:16:21.620 --> 01:16:23.328 align:middle line:84% is that for this kind of container glass, 01:16:23.328 --> 01:16:26.020 align:middle line:84% they also have to go through a process called dealkalization. 01:16:26.020 --> 01:16:30.180 align:middle line:90% 01:16:30.180 --> 01:16:34.360 align:middle line:90% So these are soda-lime glasses. 01:16:34.360 --> 01:16:36.148 align:middle line:90% They have sodium. 01:16:36.148 --> 01:16:37.940 align:middle line:84% We have mentioned that sodium-- the problem 01:16:37.940 --> 01:16:40.400 align:middle line:84% is that when it comes into contact with aqueous solutions, 01:16:40.400 --> 01:16:43.140 align:middle line:84% sodium tends to slowly leach out. 01:16:43.140 --> 01:16:46.620 align:middle line:84% And when they leach out, they become sodium hydroxide. 01:16:46.620 --> 01:16:49.320 align:middle line:84% So it turns the solution more basic. 01:16:49.320 --> 01:16:52.340 align:middle line:84% It also changes the taste of the beverage over time. 01:16:52.340 --> 01:16:55.500 align:middle line:84% So that's why, for these container glasses, 01:16:55.500 --> 01:17:03.700 align:middle line:84% they tend to add basically SO2 or SO3 01:17:03.700 --> 01:17:05.320 align:middle line:90% at the end of the process. 01:17:05.320 --> 01:17:09.300 align:middle line:84% And then they let them react with the sodium on the glass 01:17:09.300 --> 01:17:16.877 align:middle line:84% surface, which then turns them basically into sodium sulfate. 01:17:16.877 --> 01:17:19.460 align:middle line:84% Sodium sulfate is water-soluble, so you can just simply remove 01:17:19.460 --> 01:17:22.780 align:middle line:90% it using the rinsing process. 01:17:22.780 --> 01:17:24.780 align:middle line:84% Now, practically, the way they implement it, 01:17:24.780 --> 01:17:27.860 align:middle line:84% instead of using glass-- sorry, using gas here, 01:17:27.860 --> 01:17:29.900 align:middle line:84% this gas is a pollutant, so they don't want 01:17:29.900 --> 01:17:31.240 align:middle line:90% to really use the gas phase. 01:17:31.240 --> 01:17:36.940 align:middle line:84% They just put something like ammonia sulfate, for example. 01:17:36.940 --> 01:17:38.200 align:middle line:90% So it's a solid material. 01:17:38.200 --> 01:17:40.783 align:middle line:84% You put a little bit into the glass container, you heat it up, 01:17:40.783 --> 01:17:42.320 align:middle line:84% it decomposes, forms these gases. 01:17:42.320 --> 01:17:44.280 align:middle line:84% In the process, you seal the glass containers, 01:17:44.280 --> 01:17:46.572 align:middle line:84% so you don't have any kind of leakage of the pollutants 01:17:46.572 --> 01:17:47.660 align:middle line:90% into the atmosphere. 01:17:47.660 --> 01:17:49.518 align:middle line:84% After you finish the reaction, you rinse it 01:17:49.518 --> 01:17:51.060 align:middle line:84% and then you actually get the surface 01:17:51.060 --> 01:17:53.540 align:middle line:90% that's depleted of sodium. 01:17:53.540 --> 01:17:57.140 align:middle line:84% So that's also how you can help improve the chemical resistance 01:17:57.140 --> 01:18:01.180 align:middle line:90% for container glasses, OK? 01:18:01.180 --> 01:18:01.680 align:middle line:90% OK. 01:18:01.680 --> 01:18:03.580 align:middle line:90% We are right on time here. 01:18:03.580 --> 01:18:06.798 align:middle line:84% Any last-minute questions before we conclude? 01:18:06.798 --> 01:18:07.340 align:middle line:90% AUDIENCE: OK. 01:18:07.340 --> 01:18:08.810 align:middle line:90% I wanted to ask. 01:18:08.810 --> 01:18:12.370 align:middle line:84% So since the cullets, they could come 01:18:12.370 --> 01:18:15.130 align:middle line:84% from different types of glasses, did 01:18:15.130 --> 01:18:17.010 align:middle line:90% they separate the different-- 01:18:17.010 --> 01:18:18.348 align:middle line:90% PROFESSOR: They have to. 01:18:18.348 --> 01:18:18.890 align:middle line:90% They have to. 01:18:18.890 --> 01:18:20.858 align:middle line:84% I mean, if it's soda-lime-- most of soda-lime 01:18:20.858 --> 01:18:23.150 align:middle line:84% are more or less the same, so it doesn't really matter. 01:18:23.150 --> 01:18:24.817 align:middle line:84% But you really cannot mix-- for example, 01:18:24.817 --> 01:18:27.270 align:middle line:84% if you have borosilicate glasses, no, 01:18:27.270 --> 01:18:28.950 align:middle line:84% it really cannot go into the same batch. 01:18:28.950 --> 01:18:30.550 align:middle line:90% It has to be separated. 01:18:30.550 --> 01:18:31.050 align:middle line:90% Yeah. 01:18:31.050 --> 01:18:33.050 align:middle line:84% Or if you have silica glass, that's 01:18:33.050 --> 01:18:34.710 align:middle line:84% creating more problems than it solves. 01:18:34.710 --> 01:18:36.170 align:middle line:90% [LAUGHS] Yeah. 01:18:36.170 --> 01:18:38.110 align:middle line:84% So you do have to sort glasses, essentially. 01:18:38.110 --> 01:18:38.610 align:middle line:90% Yeah. 01:18:38.610 --> 01:18:41.370 align:middle line:84% And if they also have any kind of specialized coatings 01:18:41.370 --> 01:18:43.387 align:middle line:84% or any kind of contaminants or whatever, 01:18:43.387 --> 01:18:45.970 align:middle line:84% they all have to be sorted out before you go into that process 01:18:45.970 --> 01:18:46.510 align:middle line:90% there. 01:18:46.510 --> 01:18:47.490 align:middle line:90% Yeah. 01:18:47.490 --> 01:18:51.330 align:middle line:84% So that's why the best cullet is the factory's own product. 01:18:51.330 --> 01:18:53.130 align:middle line:90% It's exactly the same. 01:18:53.130 --> 01:18:55.110 align:middle line:84% Any kind of a product that doesn't qualify, 01:18:55.110 --> 01:18:57.090 align:middle line:84% it doesn't meet the quality standard 01:18:57.090 --> 01:18:58.590 align:middle line:90% just goes back as cullets. 01:18:58.590 --> 01:18:59.090 align:middle line:90% Yeah. 01:18:59.090 --> 01:19:02.170 align:middle line:90% 01:19:02.170 --> 01:19:02.970 align:middle line:90% OK. 01:19:02.970 --> 01:19:03.770 align:middle line:90% All right. 01:19:03.770 --> 01:19:05.760 align:middle line:90% Thank you very much. 01:19:05.760 --> 01:20:07.000 align:middle line:90%