WEBVTT 00:00:00.030 --> 00:00:02.400 The following content is provided under a Creative 00:00:02.400 --> 00:00:03.830 Commons license. 00:00:03.830 --> 00:00:06.850 Your support will help MIT OpenCourseWare continue to 00:00:06.850 --> 00:00:10.510 offer high-quality educational resources for free. 00:00:10.510 --> 00:00:13.390 To make a donation or view additional material from 00:00:13.390 --> 00:00:17.490 hundreds of MIT courses, visit MIT OpenCourseWare at 00:00:17.490 --> 00:00:18.740 ocw.mit.edu. 00:00:21.570 --> 00:00:21.930 PROFESSOR: All right. 00:00:21.930 --> 00:00:27.260 So today we're going to start the last section. 00:00:27.260 --> 00:00:30.980 We're going to do three lectures on phase diagrams. 00:00:30.980 --> 00:00:36.460 And I've given this the label here of Stability, Sustaining 00:00:36.460 --> 00:00:37.320 the Solid State. 00:00:37.320 --> 00:00:40.500 We've talked a lot about the solid state in 3.091 as the 00:00:40.500 --> 00:00:43.870 vehicle for teaching the rudiments of chemistry. 00:00:43.870 --> 00:00:47.370 One of the things we have not talked about, is what are the 00:00:47.370 --> 00:00:50.600 conditions that sustain the solid state? 00:00:50.600 --> 00:00:52.730 How do I know whether something's going to be a 00:00:52.730 --> 00:00:54.845 solid, or a liquid, or a gas? 00:00:54.845 --> 00:00:56.250 This is very important. 00:00:56.250 --> 00:00:59.060 For example, if you're in a foundry, you're running 00:00:59.060 --> 00:01:01.350 places, making auto parts, you have to know what the 00:01:01.350 --> 00:01:03.790 solidification temperature is of the alloys, so you can get 00:01:03.790 --> 00:01:07.150 the parts out quickly and keep productivity high. 00:01:07.150 --> 00:01:08.850 It's even important in failure analysis. 00:01:08.850 --> 00:01:11.950 You know, when they were looking at things like the 00:01:11.950 --> 00:01:16.420 rubble from the World Trade Center by understanding phase 00:01:16.420 --> 00:01:20.670 stability, the thermal history was imprinted in the metal. 00:01:20.670 --> 00:01:23.600 It's possible to determine what temperatures were 00:01:23.600 --> 00:01:27.720 achieved, and therefore, what the chain of events was that 00:01:27.720 --> 00:01:29.860 led to the collapse of those buildings. 00:01:29.860 --> 00:01:31.680 Now you might say, well, isn't this straightforward? 00:01:31.680 --> 00:01:34.350 I mean, for example, you just look up the melting point or 00:01:34.350 --> 00:01:35.200 boiling point. 00:01:35.200 --> 00:01:39.800 Water, 0 degrees C. Melting point, boiling point, 100 00:01:39.800 --> 00:01:41.210 degrees C. 00:01:41.210 --> 00:01:44.090 Well, suppose you decide to realize your life's ambition. 00:01:44.090 --> 00:01:46.150 You're going to go and scale Mount Everest. 00:01:46.150 --> 00:01:48.440 So you pay the $10,000, you get a license from the 00:01:48.440 --> 00:01:50.390 Nepalese Government, and you're at base 00:01:50.390 --> 00:01:51.710 camp at 20,000 feet. 00:01:51.710 --> 00:01:53.870 You're sitting there, you've got your campfire going, 00:01:53.870 --> 00:01:56.185 you've got a hankering for a hard-boiled egg. 00:01:56.185 --> 00:01:58.570 And you start, you put the eggs into boiling water and 00:01:58.570 --> 00:02:01.550 you cook them 10 minutes, you take them out, and they're 00:02:01.550 --> 00:02:03.020 still runny. 00:02:03.020 --> 00:02:04.550 You say, I must've lost track of time. 00:02:04.550 --> 00:02:06.940 So you cook them 20 minutes, and they're still runny. 00:02:06.940 --> 00:02:09.250 And you cook them 30 minutes, and they're still runny. 00:02:09.250 --> 00:02:12.470 And you eventually come to the realization that at 20,000 00:02:12.470 --> 00:02:17.290 feet, the boiling point of water is below the denaturing 00:02:17.290 --> 00:02:20.300 temperature of egg yolk. 00:02:20.300 --> 00:02:23.930 So now the boiling point is a function of pressure. 00:02:28.040 --> 00:02:33.360 So you know, we could have one of these Iron Chef cookoffs, 00:02:33.360 --> 00:02:40.360 only the dish is souffle, only we'll have the contest at 00:02:40.360 --> 00:02:44.510 Flagstaff, Arizona, where the altitude is so high that the 00:02:44.510 --> 00:02:48.940 classical recipes won't work, because the boiling point, the 00:02:48.940 --> 00:02:51.820 atmospheric pressure, and everything conspire so that 00:02:51.820 --> 00:02:54.235 you're not going to be able to support the souffle. 00:02:54.235 --> 00:02:56.360 So you're going to have to understand phase diagrams. 00:02:56.360 --> 00:02:59.150 In fact, if you understand phase diagrams, that's your 00:02:59.150 --> 00:03:02.650 ticket to being a four-star chef in the kitchen. 00:03:02.650 --> 00:03:05.560 Well, here's another place we can look at, where pressure 00:03:05.560 --> 00:03:06.760 has an important role. 00:03:06.760 --> 00:03:08.650 Let's look under the hood of a car. 00:03:08.650 --> 00:03:11.360 You're running an internal combustion engine. 00:03:11.360 --> 00:03:16.160 So this is the engine block, and there's 00:03:16.160 --> 00:03:17.530 combustion going on inside. 00:03:17.530 --> 00:03:19.290 We've got to keep this thing from overeating. 00:03:19.290 --> 00:03:20.620 It could damage the metal. 00:03:20.620 --> 00:03:22.510 In extreme, you could melt the metal. 00:03:22.510 --> 00:03:27.360 So we've got cooling channels in here with water flow. 00:03:27.360 --> 00:03:28.880 But then the water's going to heat up, and the 00:03:28.880 --> 00:03:29.860 water's going to boil. 00:03:29.860 --> 00:03:34.280 So we've got, over here, the radiator. 00:03:34.280 --> 00:03:36.500 So it's really a double cooling system. 00:03:36.500 --> 00:03:39.290 The water cools the block, and then the 00:03:39.290 --> 00:03:40.820 radiator cools the water. 00:03:40.820 --> 00:03:41.840 So how's that going to work? 00:03:41.840 --> 00:03:45.340 Well, here, the temperature is on the order of about 90 00:03:45.340 --> 00:03:50.110 degrees C, and here the temperature inside the engine 00:03:50.110 --> 00:03:52.680 block is much greater than 90 degrees C. It's several 00:03:52.680 --> 00:03:55.580 hundred degrees C inside that engine block, and we've got 00:03:55.580 --> 00:03:57.330 water going like this. 00:03:57.330 --> 00:04:02.270 So we've got cooling water flow in this manner. 00:04:02.270 --> 00:04:05.630 And now cold water goes in and hot water comes out, and then 00:04:05.630 --> 00:04:08.480 we get into the radiator, and we've got channels here, and 00:04:08.480 --> 00:04:11.515 we've either got a fan or some kind of air flow. 00:04:14.940 --> 00:04:17.200 And so now, what's the gambit here? 00:04:17.200 --> 00:04:20.920 I want to see what's going on inside this radiator. 00:04:20.920 --> 00:04:28.130 So if this is the wall of the radiator, and in here I've got 00:04:28.130 --> 00:04:35.220 water, and over here I've got air, the idea is to have a 00:04:35.220 --> 00:04:43.510 high heat flux to get the energy out of the water and 00:04:43.510 --> 00:04:44.750 cool it down. 00:04:44.750 --> 00:04:47.790 Now, if things get really, really hot in here-- let's say 00:04:47.790 --> 00:04:50.690 you're zooming along down the highway at about 90, I mean, 00:04:50.690 --> 00:04:54.910 about 65 miles an hour, and all of a sudden you come upon 00:04:54.910 --> 00:04:58.400 a collision, and you have to go to a dead stop, all that 00:04:58.400 --> 00:05:02.220 energy in the engine is now dumped, and 00:05:02.220 --> 00:05:03.580 the water could overheat. 00:05:03.580 --> 00:05:06.860 And in the extreme, if it overheats, it can actually go 00:05:06.860 --> 00:05:09.080 into a boil. 00:05:09.080 --> 00:05:10.070 And this is bad. 00:05:10.070 --> 00:05:14.510 Because heat transfer is really good between a liquid 00:05:14.510 --> 00:05:16.180 and a solid, and it's really poor 00:05:16.180 --> 00:05:18.780 between a gas and a solid. 00:05:18.780 --> 00:05:25.380 This is a low heat flux, and this is bad. 00:05:25.380 --> 00:05:28.220 High heat flux, that's good. 00:05:28.220 --> 00:05:29.710 This is the bubbles. 00:05:29.710 --> 00:05:32.480 This is boiling. 00:05:32.480 --> 00:05:33.520 And why? 00:05:33.520 --> 00:05:36.430 Because what transfers energy? 00:05:36.430 --> 00:05:37.370 It's the atoms. 00:05:37.370 --> 00:05:39.950 And what's the atom density in a liquid versus the atom 00:05:39.950 --> 00:05:41.230 density in a gas? 00:05:41.230 --> 00:05:44.870 You just have really crummy heat transfer. 00:05:44.870 --> 00:05:48.050 That's why insulation involves dead airspace. 00:05:48.050 --> 00:05:52.210 Because you have very poor atom density. 00:05:52.210 --> 00:05:57.080 So what can we do in order to try to 00:05:57.080 --> 00:05:59.360 repress the bubble formation? 00:05:59.360 --> 00:06:03.690 Well, we said if we went up Mount Everest, we went to high 00:06:03.690 --> 00:06:08.180 altitude, the boiling point went down. 00:06:08.180 --> 00:06:09.470 And why did it go down? 00:06:09.470 --> 00:06:11.880 Because the atmospheric pressure is lower. 00:06:11.880 --> 00:06:15.180 So why don't we go the inverse here, and we'll put a pressure 00:06:15.180 --> 00:06:18.990 cap on the radiator, and make the pressure go up, and when 00:06:18.990 --> 00:06:21.930 the pressure goes up, it exerts a back pressure and 00:06:21.930 --> 00:06:23.620 represses bubble formation? 00:06:23.620 --> 00:06:28.690 So by increasing pressure, we can increase the temperature, 00:06:28.690 --> 00:06:30.190 and get the temperature up. 00:06:30.190 --> 00:06:32.880 So let's say p equals-- if you look on the top of the 00:06:32.880 --> 00:06:36.290 pressure cap, it will say 15 psi. 00:06:36.290 --> 00:06:44.100 And 15 psi is almost 14.7 psi, which is exactly 1 atmosphere, 00:06:44.100 --> 00:06:48.020 which in SI units is, and I know this to six significant 00:06:48.020 --> 00:06:51.340 figures, 101325 Pascals. 00:06:51.340 --> 00:06:55.760 Or, you know, from Torricelli, 760 millimeters of mercury, 00:06:55.760 --> 00:06:57.510 that's the column that's supported. 00:06:57.510 --> 00:07:00.530 So we're at 2 atmospheres pressure in there, and with 00:07:00.530 --> 00:07:02.905 two atmospheres of pressure, we can raise the boiling point 00:07:02.905 --> 00:07:09.050 to 106 degrees C. And then what we can do, is now change 00:07:09.050 --> 00:07:09.970 the composition. 00:07:09.970 --> 00:07:12.970 So we change the pressure, and I change the boiling point. 00:07:12.970 --> 00:07:14.400 I change the composition. 00:07:14.400 --> 00:07:17.260 add 50% ethylene glycol. 00:07:20.320 --> 00:07:21.690 So now I've got a one-to-one mix, 00:07:21.690 --> 00:07:23.210 ethylene glycol and water. 00:07:23.210 --> 00:07:27.170 And that takes the boiling point up to 130 degrees C, or 00:07:27.170 --> 00:07:31.640 265 degrees Fahrenheit. 00:07:31.640 --> 00:07:37.600 So another example of how we can manage systems. 00:07:37.600 --> 00:07:41.030 So when I'm showing you by these several examples, is 00:07:41.030 --> 00:07:46.770 that the boiling point is a function of pressure and 00:07:46.770 --> 00:07:48.260 composition. 00:07:48.260 --> 00:07:50.640 So we can tune the boiling point. 00:07:50.640 --> 00:07:54.600 See we were tuning materials properties before. 00:07:54.600 --> 00:07:57.900 Now we're tuning physical chemical properties, because 00:07:57.900 --> 00:07:59.280 that's what chemistry is all about. 00:07:59.280 --> 00:08:00.730 It's about control. 00:08:00.730 --> 00:08:02.430 It's about management. 00:08:02.430 --> 00:08:05.220 Management to advantage. 00:08:05.220 --> 00:08:08.270 So how do we know what to do here? 00:08:08.270 --> 00:08:10.240 Can we predict this from first principles? 00:08:10.240 --> 00:08:11.080 No. 00:08:11.080 --> 00:08:12.860 Systems are still too complicated. 00:08:12.860 --> 00:08:14.390 Our models aren't robust enough. 00:08:14.390 --> 00:08:18.150 So instead, we turn to an archive. 00:08:18.150 --> 00:08:20.165 So we have phase diagrams. 00:08:22.800 --> 00:08:27.370 And the phase diagrams guide us in our search for better 00:08:27.370 --> 00:08:30.140 management of material systems. 00:08:30.140 --> 00:08:32.670 And these are stability maps. 00:08:32.670 --> 00:08:35.570 They tell us which phases are stable under which conditions 00:08:35.570 --> 00:08:39.100 of pressure, temperature, composition. 00:08:39.100 --> 00:08:41.220 You can consider them as archives. 00:08:45.070 --> 00:08:47.460 So that's what I want to talk about, because it's really 00:08:47.460 --> 00:08:49.540 important to know this stuff. 00:08:49.540 --> 00:08:49.950 OK. 00:08:49.950 --> 00:08:51.190 So what are we going to do? 00:08:51.190 --> 00:08:53.510 So first of all, let's-- 00:08:53.510 --> 00:08:54.650 I don't want to write on that one. 00:08:54.650 --> 00:08:55.400 This is interesting. 00:08:55.400 --> 00:08:56.960 This could be a work of art. 00:08:56.960 --> 00:08:58.850 I'd hate to desecrate it. 00:08:58.850 --> 00:08:59.860 You like? 00:08:59.860 --> 00:09:02.250 This is really good! 00:09:02.250 --> 00:09:03.540 So I'm just going to leave that. 00:09:03.540 --> 00:09:07.680 That's very good. 00:09:07.680 --> 00:09:08.330 That's excellent. 00:09:08.330 --> 00:09:08.630 OK. 00:09:08.630 --> 00:09:12.200 So I've been talking about phase. 00:09:12.200 --> 00:09:13.080 What is a phase? 00:09:13.080 --> 00:09:14.490 Let's get the right definition here. 00:09:14.490 --> 00:09:15.440 What is a phase? 00:09:15.440 --> 00:09:19.920 It's a region uniform chemical composition. 00:09:19.920 --> 00:09:21.940 Just to get it down. 00:09:21.940 --> 00:09:25.630 it's a region in a material, region of uniform chemical 00:09:25.630 --> 00:09:33.060 composition, and it has these other properties. 00:09:33.060 --> 00:09:35.130 Uniform chemical composition. 00:09:35.130 --> 00:09:38.790 It's physically distinct. 00:09:38.790 --> 00:09:41.130 And I'll show you by examples, but let's just get the 00:09:41.130 --> 00:09:42.340 definition down. 00:09:42.340 --> 00:09:45.980 It's physically distinct, and in the extreme case-- 00:09:45.980 --> 00:09:47.500 so that means it's bounded. 00:09:47.500 --> 00:09:48.710 It's physically distinct. 00:09:48.710 --> 00:09:51.460 That's a fancy way of saying that you can put a 00:09:51.460 --> 00:09:53.150 boundary around it. 00:09:53.150 --> 00:09:54.480 It's bounded. 00:09:54.480 --> 00:09:57.490 And then the other property that it has, it's mechanically 00:09:57.490 --> 00:09:58.740 separable in the extreme. 00:10:05.930 --> 00:10:09.320 And so that's in the case where you have 00:10:09.320 --> 00:10:10.640 a multi-phase system. 00:10:10.640 --> 00:10:12.730 You can point to the different p. 00:10:12.730 --> 00:10:14.450 So what I'm going to do, is I'm going to 00:10:14.450 --> 00:10:15.430 give you some examples. 00:10:15.430 --> 00:10:20.400 And so I'm going to let circle p equal number of phases. 00:10:23.200 --> 00:10:24.530 I'll give you some examples. 00:10:24.530 --> 00:10:25.870 Why am I using circle p? 00:10:25.870 --> 00:10:28.720 Because just plain old p is already pressure. 00:10:28.720 --> 00:10:31.410 So pressure, so this is kind of a Western motif, you know? 00:10:31.410 --> 00:10:33.800 Like a Circle Bar Ranch or something. 00:10:33.800 --> 00:10:34.890 So it's a p with a circle. 00:10:34.890 --> 00:10:36.640 That's my font. 00:10:36.640 --> 00:10:38.110 That's how I say number of phases. 00:10:38.110 --> 00:10:40.600 So let's take a look at some examples. 00:10:40.600 --> 00:10:43.760 So here's some examples of p equals 1. 00:10:43.760 --> 00:10:46.730 So simple one is pure water. 00:10:46.730 --> 00:10:47.980 Pure H2O liquid. 00:10:47.980 --> 00:10:49.300 It has all of this. 00:10:49.300 --> 00:10:52.700 Wherever I have the water, all right, here's some water, it's 00:10:52.700 --> 00:10:55.200 all of the same chemical composition. 00:10:55.200 --> 00:10:56.940 It is physically distinct. 00:10:56.940 --> 00:10:58.510 I can put a boundary around it. 00:10:58.510 --> 00:11:00.840 And in this case, there's nothing to separate, because 00:11:00.840 --> 00:11:03.010 it's just a one-phase system. 00:11:03.010 --> 00:11:05.480 White gold. 00:11:05.480 --> 00:11:07.170 White gold is one phase. 00:11:07.170 --> 00:11:09.050 Because we have gold. 00:11:09.050 --> 00:11:10.160 Obviously we have gold. 00:11:10.160 --> 00:11:12.570 If you market something as white gold, it has no gold, 00:11:12.570 --> 00:11:13.620 you'll go to prison. 00:11:13.620 --> 00:11:17.270 And how do we make white gold go to its white color from the 00:11:17.270 --> 00:11:18.190 normal yellow? 00:11:18.190 --> 00:11:19.930 We add silver and we add nickel. 00:11:19.930 --> 00:11:23.100 And these are all FCC metals, and they substitute for one 00:11:23.100 --> 00:11:25.670 another on the lattice, and if you sample anywhere in the 00:11:25.670 --> 00:11:27.700 white gold, you get the same chemical 00:11:27.700 --> 00:11:29.410 composition, and so on. 00:11:29.410 --> 00:11:31.970 Air is an example of a one-phase system. 00:11:31.970 --> 00:11:35.230 It's a gas, and in decreasing order, we 00:11:35.230 --> 00:11:36.860 have nitrogen, oxygen. 00:11:36.860 --> 00:11:37.900 So it's a solution. 00:11:37.900 --> 00:11:39.590 We're breathing a solution. 00:11:39.590 --> 00:11:43.600 Nitrogen, oxygen, argon are the main constituents. 00:11:43.600 --> 00:11:47.730 There's some CO2, some sulfur dioxide if you live near a 00:11:47.730 --> 00:11:50.870 power plant, NOx if you're near a tailpipe, and 00:11:50.870 --> 00:11:52.490 so on and so forth. 00:11:52.490 --> 00:11:59.740 And then the last one I'll give as an example is 00:11:59.740 --> 00:12:00.990 calcia-zirconia. 00:12:02.760 --> 00:12:03.820 Or cubic zirconia. 00:12:03.820 --> 00:12:06.530 Let's just call it cubic zirconia. 00:12:06.530 --> 00:12:09.010 The holidays are coming, so we better get 00:12:09.010 --> 00:12:10.460 cubic zirconia up here. 00:12:10.460 --> 00:12:11.950 That's the poor man's diamond. 00:12:11.950 --> 00:12:16.100 Cubic zirconia, which consists of a solid solution of calcium 00:12:16.100 --> 00:12:18.700 oxide in zirconium oxide. 00:12:18.700 --> 00:12:23.160 This is a solid solution, so it's continuous and chemical 00:12:23.160 --> 00:12:25.230 composition identical. 00:12:25.230 --> 00:12:29.920 Now, contrast that with two-phase system. 00:12:29.920 --> 00:12:31.640 So p equals 2 looks like this. 00:12:31.640 --> 00:12:35.830 So let's look at, instead of simple water liquid, if I have 00:12:35.830 --> 00:12:37.320 ice cubes in water. 00:12:40.560 --> 00:12:43.980 So now I have two different phases, and they're separated 00:12:43.980 --> 00:12:46.720 by state of matter. 00:12:46.720 --> 00:12:49.290 State of matter is the issue here. 00:12:49.290 --> 00:12:51.000 Because I have a solid-- 00:12:51.000 --> 00:12:52.400 this is solid-- 00:12:52.400 --> 00:12:54.490 and I'm going to put the boundary around them. 00:12:54.490 --> 00:12:58.170 The composition of the solid is different from the 00:12:58.170 --> 00:12:59.300 composition of liquid. 00:12:59.300 --> 00:13:01.820 They're both the same water, but you can tell it's a 00:13:01.820 --> 00:13:03.740 different crystal structure and so on. 00:13:03.740 --> 00:13:06.820 And I can put boundaries around, and it's 00:13:06.820 --> 00:13:07.910 mechanically separable. 00:13:07.910 --> 00:13:09.880 You can pull the ice cubes out of the mix. 00:13:09.880 --> 00:13:11.710 Milk is two-phase. 00:13:11.710 --> 00:13:16.780 Milk has a fatty phase and it has an aqueous phase. 00:13:16.780 --> 00:13:18.650 The aqueous phase contains the minerals. 00:13:18.650 --> 00:13:20.650 That's why you can drink skim milk and still get your 00:13:20.650 --> 00:13:23.560 calcium, because calcium, even the general public knows 00:13:23.560 --> 00:13:25.030 calcium is a mineral. 00:13:25.030 --> 00:13:28.050 It's not elemental calcium, it's a calcium compound. 00:13:28.050 --> 00:13:32.290 But it's ionic, it's soluble in water, and the fat contains 00:13:32.290 --> 00:13:33.150 the other parts. 00:13:33.150 --> 00:13:36.730 You know from last day, this is one of the lipids. 00:13:36.730 --> 00:13:39.910 And so you have fat globules that are mechanically 00:13:39.910 --> 00:13:42.150 separable and distinct from aqueous. 00:13:42.150 --> 00:13:43.730 So they actually have a different chemical 00:13:43.730 --> 00:13:46.370 composition, different type of bonding. 00:13:46.370 --> 00:13:46.640 Right? 00:13:46.640 --> 00:13:50.500 This is largely nonpolar, and nonpolar doesn't like to 00:13:50.500 --> 00:13:54.990 dissolve in something that is polar and hydrogen-bonded. 00:13:54.990 --> 00:13:56.860 So they phase separate. 00:13:56.860 --> 00:13:58.580 I've been saying phase separate all along. 00:13:58.580 --> 00:14:01.290 Now you know what we mean by phase separate. 00:14:01.290 --> 00:14:02.890 Here's a third one. 00:14:02.890 --> 00:14:05.500 This is really cool, because you won't get this in any 00:14:05.500 --> 00:14:08.640 other chemistry class, because only 3.091 00:14:08.640 --> 00:14:10.060 talks about such things. 00:14:10.060 --> 00:14:12.100 David, can we cut to the document camera? 00:14:12.100 --> 00:14:14.580 I want to show you a piece of snowflake obsidian. 00:14:18.870 --> 00:14:21.880 Obsidian is a volcanic glass. 00:14:27.060 --> 00:14:28.450 So here's the piece of obsidian. 00:14:28.450 --> 00:14:33.410 And what you're looking at is, the black area is the glassy 00:14:33.410 --> 00:14:38.000 part, and the white is actually some of the obsidian 00:14:38.000 --> 00:14:40.510 that has decided to devitrify. 00:14:40.510 --> 00:14:42.200 And it is turning crystalline. 00:14:42.200 --> 00:14:47.560 And so those are islands of obsidian crystal sitting in a 00:14:47.560 --> 00:14:51.305 matrix of obsidian glass. 00:14:51.305 --> 00:14:54.460 If we go back to the-- 00:14:54.460 --> 00:14:57.020 I picked that up in Yellowstone Park. 00:14:57.020 --> 00:14:57.980 It's fantastic. 00:14:57.980 --> 00:15:01.690 There's a wall, just a wall of obsidian that comes down. 00:15:01.690 --> 00:15:05.150 And I think I've got an image here. 00:15:05.150 --> 00:15:05.720 There it is. 00:15:05.720 --> 00:15:09.060 This one I pulled off the internet. 00:15:09.060 --> 00:15:12.720 So this is crystalline phase, and this is 00:15:12.720 --> 00:15:14.200 the amorphous phase. 00:15:14.200 --> 00:15:18.030 And the overall composition, it's a glass, it's a silicate. 00:15:18.030 --> 00:15:20.050 And why isn't it transparent to visible light? 00:15:20.050 --> 00:15:21.440 Because it's got iron in it. 00:15:21.440 --> 00:15:24.400 The iron gives it the absorption and capabilities. 00:15:24.400 --> 00:15:27.250 The band gap is invisible, so it's black. 00:15:27.250 --> 00:15:29.500 But then when this crystallizes, it's got a 00:15:29.500 --> 00:15:32.060 different index, and it's mainly SiO2. 00:15:32.060 --> 00:15:35.740 It's really the cristobalite phase of the obsidian. 00:15:35.740 --> 00:15:37.180 So that's cool. 00:15:37.180 --> 00:15:41.690 So this is actually differentiated on the basis of 00:15:41.690 --> 00:15:50.700 amorphous and crystalline of something that's virtually the 00:15:50.700 --> 00:15:51.960 same chemical composition. 00:15:51.960 --> 00:15:57.020 So this could give you an idea of what happens in the area of 00:15:57.020 --> 00:15:58.660 phase separation. 00:15:58.660 --> 00:15:59.430 OK. 00:15:59.430 --> 00:16:02.340 Now the second thing that I have to bring to your 00:16:02.340 --> 00:16:05.830 attention, is that these phase diagrams treat systems at 00:16:05.830 --> 00:16:07.150 equilibrium. 00:16:07.150 --> 00:16:09.990 They're stability maps, and they treat systems at 00:16:09.990 --> 00:16:10.680 equilibrium. 00:16:10.680 --> 00:16:12.560 So what is equilibrium? 00:16:12.560 --> 00:16:16.340 Let's just get one time up here a definition of 00:16:16.340 --> 00:16:17.000 equilibrium. 00:16:17.000 --> 00:16:22.680 Equilibrium is a condition which there is no net reaction 00:16:22.680 --> 00:16:23.270 taking place. 00:16:23.270 --> 00:16:24.540 The system could be reacting. 00:16:24.540 --> 00:16:27.230 If you're looking at the ice cubes in water, the ice could 00:16:27.230 --> 00:16:30.260 be dissolving, and some of the water could be freezing, but 00:16:30.260 --> 00:16:33.430 overall, with time, there's no net reaction. 00:16:33.430 --> 00:16:36.420 It's a dynamic system with no net reaction. 00:16:36.420 --> 00:16:39.430 And it's characterized as the lowest energy state. 00:16:42.590 --> 00:16:46.270 Systems strive towards equilibrium. 00:16:46.270 --> 00:16:49.040 If it's the lowest energy state, no net reaction then. 00:16:49.040 --> 00:16:52.050 If a system is truly at equilibrium, the properties 00:16:52.050 --> 00:16:55.190 should be invariant over time, because 00:16:55.190 --> 00:16:58.130 there's no net reaction. 00:16:58.130 --> 00:16:59.980 You can't prove equilibrium. 00:16:59.980 --> 00:17:03.150 You can only demonstrate the absence of equilibrium. 00:17:03.150 --> 00:17:04.990 Because at equilibrium, there's nothing, there's no 00:17:04.990 --> 00:17:06.240 net reaction. 00:17:11.950 --> 00:17:14.070 And it could be attainable by multiple paths. 00:17:14.070 --> 00:17:18.910 So in other words, if I have ice as the equilibrium phase, 00:17:18.910 --> 00:17:22.940 I can make it by freezing water, and get to the same ice 00:17:22.940 --> 00:17:24.700 at the given temperature and pressure. 00:17:24.700 --> 00:17:26.960 Or I could sublime. 00:17:26.960 --> 00:17:31.150 But if I specify the pressure and the composition, I should 00:17:31.150 --> 00:17:33.100 always end up with the same system. 00:17:33.100 --> 00:17:35.663 So attainable by multiple paths. 00:17:41.030 --> 00:17:42.900 Because it's a stable state, so it doesn't 00:17:42.900 --> 00:17:44.490 matter how you got there. 00:17:44.490 --> 00:17:45.440 It's a state function. 00:17:45.440 --> 00:17:47.840 And you know from your physics, a state function has 00:17:47.840 --> 00:17:50.880 the same value, regardless of how you arrived there. 00:17:50.880 --> 00:17:53.400 And then the last thing is, I want to differentiate. 00:17:53.400 --> 00:17:56.370 See, these are all single phase, but some of them are 00:17:56.370 --> 00:18:00.470 just one element, some of them are just one compound, and 00:18:00.470 --> 00:18:01.720 some of them have a whole mix. 00:18:01.720 --> 00:18:05.780 So we have a way of quantifying the degree of 00:18:05.780 --> 00:18:10.270 chemical complexity by using the term called component. 00:18:10.270 --> 00:18:12.195 It's a measure of chemical complexity. 00:18:21.790 --> 00:18:27.715 It's the number of chemically distinguishable constituents. 00:18:32.670 --> 00:18:34.060 And again, these are definitions. 00:18:34.060 --> 00:18:38.160 I'll give you some examples so then the 00:18:38.160 --> 00:18:40.880 definition comes to life. 00:18:40.880 --> 00:18:43.395 I like to think of it as the number of bottles you've got 00:18:43.395 --> 00:18:47.460 to pull off the shelf to make the final product. 00:18:47.460 --> 00:18:48.210 The building blocks. 00:18:48.210 --> 00:18:49.950 So for example, water is just water. 00:18:49.950 --> 00:18:51.580 You could say, but it's hydrogen and oxygen. 00:18:51.580 --> 00:18:54.830 But if you take 560 or some other thermal class, you'll 00:18:54.830 --> 00:18:57.560 learn that they're bound by mole ratio. 00:18:57.560 --> 00:19:00.220 You don't have freedom of hydrogen and oxygen. 00:19:00.220 --> 00:19:02.980 So it's just one bottle, whereas to make white gold, 00:19:02.980 --> 00:19:05.600 you need three bottles. 00:19:05.600 --> 00:19:07.810 You need a bottle of gold, a bottle of silver, 00:19:07.810 --> 00:19:08.590 and a bottle of nickel. 00:19:08.590 --> 00:19:10.240 So that's a three component system. 00:19:10.240 --> 00:19:13.440 And I'm going to designate the components by c with a 00:19:13.440 --> 00:19:14.280 circle around it. 00:19:14.280 --> 00:19:18.670 Because c without a circle is already composition, 00:19:18.670 --> 00:19:20.270 concentration. 00:19:20.270 --> 00:19:20.560 OK. 00:19:20.560 --> 00:19:25.160 So now we can put all of this together, and we'll show the 00:19:25.160 --> 00:19:28.480 difference between multicomponent and multiphase. 00:19:28.480 --> 00:19:33.070 So we'll make a little table here, and here I'm going to 00:19:33.070 --> 00:19:37.260 talk about one-phase systems, and distinguish on the basis 00:19:37.260 --> 00:19:38.320 of components. 00:19:38.320 --> 00:19:42.540 So if it's single phase single component, that's just water. 00:19:42.540 --> 00:19:43.860 One phase, one component. 00:19:43.860 --> 00:19:45.160 Simple liquid. 00:19:45.160 --> 00:19:50.640 If it's two components one phase, that could be 00:19:50.640 --> 00:19:52.930 calcia-zirconia. 00:19:52.930 --> 00:19:56.340 I need a bottle of calcia and a bottle of zirconia in order 00:19:56.340 --> 00:20:00.350 to make this two component single-phase system. 00:20:00.350 --> 00:20:02.320 And then to have three components, 00:20:02.320 --> 00:20:05.070 that's the white gold. 00:20:05.070 --> 00:20:09.680 It's still single phase, but I need the gold, silver, and the 00:20:09.680 --> 00:20:12.860 nickel, whereas if I come over here, I've got two phases. 00:20:12.860 --> 00:20:15.480 That could be slush. 00:20:15.480 --> 00:20:16.910 Slush, that's ice water. 00:20:20.360 --> 00:20:21.420 It's just one component. 00:20:21.420 --> 00:20:26.550 I just start with water, and drop it down to 0 Centigrade, 00:20:26.550 --> 00:20:29.230 and I'm going to end up with ice crystals in the water. 00:20:29.230 --> 00:20:30.600 So that's one component. 00:20:30.600 --> 00:20:31.930 I just needed one bottle. 00:20:31.930 --> 00:20:33.800 Literally, one bottle. 00:20:33.800 --> 00:20:34.230 All right. 00:20:34.230 --> 00:20:37.210 Now what about two components, two phases? 00:20:37.210 --> 00:20:39.950 Well, we saw earlier when we started thinking about 00:20:39.950 --> 00:20:43.720 solubility, we did the bilayer with carbon 00:20:43.720 --> 00:20:45.690 tetrachloride and water. 00:20:45.690 --> 00:20:49.270 Remember, we dropped potassium permanganate and iodine, and 00:20:49.270 --> 00:20:51.380 the potassium permanganate dissolved in the water, and 00:20:51.380 --> 00:20:53.540 the iodine dissolved in the carbon tetrachloride? 00:20:53.540 --> 00:20:55.200 Two different components. 00:20:55.200 --> 00:20:57.550 I need a bottle of carbon tet and a bottle of water. 00:20:57.550 --> 00:20:59.010 And they'll phase separate. 00:20:59.010 --> 00:21:01.150 They don't dissolve in one another, because this is a 00:21:01.150 --> 00:21:04.460 nonpolar liquid, and this is polar hydrogen bonded. 00:21:04.460 --> 00:21:06.890 That's the origin of phase separation. 00:21:06.890 --> 00:21:08.700 It's all about bonding, and bonding is all about 00:21:08.700 --> 00:21:11.690 electronic structure, and that sounds like a good topic for a 00:21:11.690 --> 00:21:13.280 class in chemistry. 00:21:13.280 --> 00:21:15.260 And then the last one here is obsidian. 00:21:19.260 --> 00:21:22.780 The snowflake obsidian, in which the 00:21:22.780 --> 00:21:25.220 components are SiO2-- 00:21:25.220 --> 00:21:27.020 so I'm going to have three components and 00:21:27.020 --> 00:21:28.070 end up with two phases. 00:21:28.070 --> 00:21:32.210 SiO2, there's some magnesia, and then the black comes from 00:21:32.210 --> 00:21:33.710 the magnetite. 00:21:33.710 --> 00:21:34.670 Fe304. 00:21:34.670 --> 00:21:37.610 So I've got three bottles off the shelf, and I end up with 00:21:37.610 --> 00:21:40.990 something that is crystalline and amorphous. 00:21:40.990 --> 00:21:42.830 So that's where I get the two phases. 00:21:42.830 --> 00:21:45.040 Three components, two phases. 00:21:45.040 --> 00:21:46.540 It's great. 00:21:46.540 --> 00:21:48.560 So now I want to look at some stability maps. 00:21:48.560 --> 00:21:51.290 And I'm going to start with the simplest of all, which is 00:21:51.290 --> 00:21:53.030 the one we know best from human 00:21:53.030 --> 00:21:55.030 experience, and that's water. 00:21:55.030 --> 00:21:56.910 So we're going to look at the one-- 00:21:56.910 --> 00:22:00.150 so it's a one component. 00:22:00.150 --> 00:22:09.830 So for water, we start with c equals 1, and the example is 00:22:09.830 --> 00:22:11.470 going to be water. 00:22:11.470 --> 00:22:13.150 One component phase diagram. 00:22:13.150 --> 00:22:17.890 So we don't have a composition axis, because the only thing 00:22:17.890 --> 00:22:20.300 we can vary is pressure and temperature. 00:22:20.300 --> 00:22:22.760 If we change composition, we've lost water. 00:22:22.760 --> 00:22:27.860 So it has to be axiomatically, no variation composition. 00:22:27.860 --> 00:22:30.660 All we have is that the coordinates of 00:22:30.660 --> 00:22:35.080 temperature and pressure. 00:22:35.080 --> 00:22:38.160 So there it is out of the book, and I'm going to draw it 00:22:38.160 --> 00:22:42.740 a little bit differently, just to emphasize three of my 00:22:42.740 --> 00:22:43.500 favorite words. 00:22:43.500 --> 00:22:45.490 Not to scale. 00:22:45.490 --> 00:22:47.370 Otherwise you can't see some of the subtle features. 00:22:47.370 --> 00:22:51.005 So overall, it's a y-shaped diagram. 00:22:53.600 --> 00:22:55.020 And this is pressure. 00:22:55.020 --> 00:22:56.970 Let's make it pressure in atmospheres. 00:23:00.820 --> 00:23:03.410 Then our human experiences is at 1 atmosphere. 00:23:06.650 --> 00:23:09.400 So at the highest temperatures, we expect to 00:23:09.400 --> 00:23:16.125 have vapor, and at the lowest temperatures, we expect solid. 00:23:19.460 --> 00:23:22.660 And in between, we expect liquid. 00:23:22.660 --> 00:23:27.020 And then if we look at the 1 atmosphere isobar, what's 00:23:27.020 --> 00:23:28.440 happening on this line? 00:23:28.440 --> 00:23:30.500 On the one side of line it's liquid, and the other side of 00:23:30.500 --> 00:23:31.460 line, it's vapor. 00:23:31.460 --> 00:23:34.550 At this temperature, liquid and vapor coexist. 00:23:34.550 --> 00:23:36.030 I call that the boiling point. 00:23:36.030 --> 00:23:37.510 So I'm going to put 100 here. 00:23:40.420 --> 00:23:45.180 And we already learned from our little example of Mount 00:23:45.180 --> 00:23:48.920 Everest that this locust here, this line, is the liquid 00:23:48.920 --> 00:23:52.050 equals vapor two phase equilibrium. 00:23:52.050 --> 00:23:53.500 And you see how it changes? 00:23:53.500 --> 00:23:56.390 If I go to the top of Mount Everest, the pressure is less 00:23:56.390 --> 00:23:57.410 than 1 atmosphere. 00:23:57.410 --> 00:23:59.940 which means the boiling point of water is below the 00:23:59.940 --> 00:24:00.930 denaturing point. 00:24:00.930 --> 00:24:02.810 So this actually gives you the map. 00:24:02.810 --> 00:24:06.420 Or if I put the pressure cap on, I go up here. 00:24:06.420 --> 00:24:08.540 And you can use this in the kitchen again. 00:24:08.540 --> 00:24:12.420 If you love wild rice, and you can't wait 45 minutes when you 00:24:12.420 --> 00:24:14.760 get home, use a pressure cooker. 00:24:14.760 --> 00:24:17.750 What the pressure cooker does, is it allows you to have 00:24:17.750 --> 00:24:21.100 liquid up to 130 degrees Celsius. 00:24:21.100 --> 00:24:22.050 See, you can't steam it. 00:24:22.050 --> 00:24:23.940 You've got to soak it in water. 00:24:23.940 --> 00:24:25.175 And you know the Arrhenius Law. 00:24:25.175 --> 00:24:28.490 If you can get the temperature up by 30 degrees, you'll cut 00:24:28.490 --> 00:24:30.440 the cooking time in half. 00:24:30.440 --> 00:24:34.460 So how do you get water, liquid, at 130 degrees? 00:24:34.460 --> 00:24:36.920 Then you can cook quicker! 00:24:36.920 --> 00:24:38.240 Pressure. 00:24:38.240 --> 00:24:38.730 Seal it. 00:24:38.730 --> 00:24:42.240 And then you've got liquid water way, way up here. 00:24:42.240 --> 00:24:46.630 Now over here, this is solid goes to liquid. 00:24:46.630 --> 00:24:48.530 So this is the freezing point line. 00:24:48.530 --> 00:24:50.500 At 1 atmosphere, that's 0. 00:24:50.500 --> 00:24:51.600 0 Celsius. 00:24:51.600 --> 00:24:53.370 And you know, if you go skating-- 00:24:53.370 --> 00:24:56.720 so let's say the ice is minus 5 Celsius. 00:24:56.720 --> 00:24:59.350 And you're here, but you put your weight on the blades, and 00:24:59.350 --> 00:25:01.270 the blades have small area. 00:25:01.270 --> 00:25:05.410 So pressure is force per area. 00:25:05.410 --> 00:25:07.900 So that puts you up here, and now you cross, and now you 00:25:07.900 --> 00:25:11.170 glide on water. 00:25:11.170 --> 00:25:12.360 Film of water. 00:25:12.360 --> 00:25:13.870 You ever watch a hockey game? 00:25:13.870 --> 00:25:14.730 I grew up in Canada. 00:25:14.730 --> 00:25:16.580 We used to say, well, the ice is fast. 00:25:16.580 --> 00:25:18.520 Why is the ice fast? 00:25:18.520 --> 00:25:22.700 Because you get down to temperatures where you just 00:25:22.700 --> 00:25:24.335 get the right slickness of water. 00:25:24.335 --> 00:25:27.580 If the ice is slow, the temperature is so close that, 00:25:27.580 --> 00:25:29.910 you know, you get these big, bruising hockey players, and 00:25:29.910 --> 00:25:31.210 they're moving up into here, and it's 00:25:31.210 --> 00:25:32.770 like they're dragging. 00:25:32.770 --> 00:25:37.050 And if you ever come from Minnesota or North Dakota, if 00:25:37.050 --> 00:25:39.560 you've ever skated when the temperature gets down about 00:25:39.560 --> 00:25:43.050 minus 20, minus 30? 00:25:43.050 --> 00:25:44.630 It's a different experience, because you never 00:25:44.630 --> 00:25:45.820 get across this line. 00:25:45.820 --> 00:25:49.950 Your blades are just, they can't get a good grip. 00:25:49.950 --> 00:25:50.250 See? 00:25:50.250 --> 00:25:51.490 Everything you need to know is here. 00:25:51.490 --> 00:25:54.800 This is four-star chef, this is 00:25:54.800 --> 00:25:56.780 prize-winning hockey player. 00:25:56.780 --> 00:25:59.530 We haven't got off the 1 atmosphere line yet. 00:25:59.530 --> 00:25:59.870 OK. 00:25:59.870 --> 00:26:02.110 So now I'm going to say, this is single phase, right? 00:26:02.110 --> 00:26:03.360 It's just vapor. 00:26:03.360 --> 00:26:05.870 This is single phase, and this is single phase. 00:26:05.870 --> 00:26:08.130 It's all solid. 00:26:08.130 --> 00:26:11.510 And along this line, it's two phase, isn't it? 00:26:14.970 --> 00:26:16.040 Solid-liquid. 00:26:16.040 --> 00:26:17.250 This is ice cubes, isn't it. 00:26:17.250 --> 00:26:20.410 Anywhere along this line is ice cubes in water. 00:26:20.410 --> 00:26:22.370 Look at this one. 00:26:22.370 --> 00:26:23.750 This is liquid vapor. 00:26:23.750 --> 00:26:25.890 This is solid, liquid-- 00:26:25.890 --> 00:26:30.210 all three of them coexist here. 00:26:30.210 --> 00:26:36.910 This is p equals 3, which means, ice cubes floating in 00:26:36.910 --> 00:26:38.160 boiling water. 00:26:41.370 --> 00:26:42.940 And this happens at only one point. 00:26:42.940 --> 00:26:50.270 It's called the triple point, and its coordinates are-- 00:26:50.270 --> 00:26:51.480 this is not to scale. 00:26:51.480 --> 00:26:55.610 So this is 0.01 degrees C. It's a 00:26:55.610 --> 00:26:57.460 1/100 of a degree higher. 00:26:57.460 --> 00:27:03.730 And the pressure here is 4.58 millimeters of mercury, which 00:27:03.730 --> 00:27:08.080 then you can convert using the 760 as 1 atmosphere. 00:27:08.080 --> 00:27:10.070 Oh, and this is solid-vapor. 00:27:10.070 --> 00:27:12.000 You can go directly from solid to vapor down here. 00:27:12.000 --> 00:27:15.300 If you hang up your clothes on a line and it's minus 20 00:27:15.300 --> 00:27:16.800 degrees outside, first thing that 00:27:16.800 --> 00:27:17.890 happens, the clothes freeze. 00:27:17.890 --> 00:27:19.330 You come back five hours later, and 00:27:19.330 --> 00:27:20.080 the clothes are dry. 00:27:20.080 --> 00:27:20.660 Well, what happened? 00:27:20.660 --> 00:27:22.580 Did somebody take them in? 00:27:22.580 --> 00:27:24.820 Run them around the clothes dryer, then 00:27:24.820 --> 00:27:25.750 hang them up for you? 00:27:25.750 --> 00:27:25.920 No. 00:27:25.920 --> 00:27:30.340 You're going directly from solid to vapor, down in here. 00:27:30.340 --> 00:27:32.590 So here's the whole story of the phase diagram. 00:27:32.590 --> 00:27:34.930 One last thing I want to point out. 00:27:34.930 --> 00:27:39.530 Here, you're at a given temperature and it's vapor. 00:27:39.530 --> 00:27:42.390 And then you squeeze, squeeze, squeeze, and now things get 00:27:42.390 --> 00:27:44.390 closer together, and you go from paper to liquid at 00:27:44.390 --> 00:27:45.180 constant temperature. 00:27:45.180 --> 00:27:46.290 That makes sense, right? 00:27:46.290 --> 00:27:48.430 I start from vapor, constant temperature. 00:27:48.430 --> 00:27:50.740 I squeeze it, I get liquid, I keep squeezing, 00:27:50.740 --> 00:27:52.150 I should make solid. 00:27:52.150 --> 00:27:52.980 Here's vapor. 00:27:52.980 --> 00:27:54.510 I squeeze, I get solid, and I squeeze 00:27:54.510 --> 00:27:55.550 harder, and I get liquid. 00:27:55.550 --> 00:27:59.910 That makes no sense at all, but that's what happens. 00:27:59.910 --> 00:28:00.850 What does this tell me? 00:28:00.850 --> 00:28:04.680 It tells me that the number of nearest neighbors in the solid 00:28:04.680 --> 00:28:05.900 is greater than the vapor. 00:28:05.900 --> 00:28:06.700 Yeah, I get that. 00:28:06.700 --> 00:28:09.040 But the number of nearest neighbors in the liquid must 00:28:09.040 --> 00:28:10.420 be greater than the number of nearest 00:28:10.420 --> 00:28:11.770 neighbors in the solid. 00:28:11.770 --> 00:28:12.980 This is an exception. 00:28:12.980 --> 00:28:16.480 When I see this negative slope, it means that ice cubes 00:28:16.480 --> 00:28:18.100 are going to float on water. 00:28:18.100 --> 00:28:20.170 That's what I learn from this negative slope. 00:28:20.170 --> 00:28:21.520 So let's put that down. 00:28:21.520 --> 00:28:26.020 dp by dt when dp by dt is less than zero. 00:28:26.020 --> 00:28:27.870 This is for solid equals liquid. 00:28:27.870 --> 00:28:31.880 That means that the density of the solid is less than the 00:28:31.880 --> 00:28:34.640 density of the liquid. 00:28:34.640 --> 00:28:36.350 All from here. 00:28:36.350 --> 00:28:36.780 OK. 00:28:36.780 --> 00:28:38.640 Good. 00:28:38.640 --> 00:28:42.810 So let's look at a few other phase diagrams. 00:28:42.810 --> 00:28:46.020 I think I've got a few things up here. 00:28:46.020 --> 00:28:47.980 Here's silicon. 00:28:47.980 --> 00:28:49.290 Pressure versus temperature. 00:28:49.290 --> 00:28:51.940 Its normal melting point is about-- 00:28:51.940 --> 00:28:53.650 see, now I said normal melting point. 00:28:53.650 --> 00:28:55.920 After today's lecture, if somebody says, what's the 00:28:55.920 --> 00:28:57.000 boiling point of water? 00:28:57.000 --> 00:28:58.050 You don't go, 100 degrees. 00:28:58.050 --> 00:28:59.300 You say, at what pressure? 00:29:01.935 --> 00:29:03.780 And they go, oh, I hate you. 00:29:03.780 --> 00:29:05.020 I hated you before. 00:29:05.020 --> 00:29:05.990 I'm going to use an adverb here. 00:29:05.990 --> 00:29:07.020 Now I really hate you. 00:29:07.020 --> 00:29:07.630 OK. 00:29:07.630 --> 00:29:10.150 So this is the normal melting point of silicon. 00:29:10.150 --> 00:29:14.110 It's about 1430 degrees Centigrade, or a 1700 00:29:14.110 --> 00:29:15.150 something Kelvin. 00:29:15.150 --> 00:29:18.080 And it also has this negative slope. 00:29:18.080 --> 00:29:18.980 And what does that tell you? 00:29:18.980 --> 00:29:22.510 That liquid silicon is denser than solid silicon, and it's a 00:29:22.510 --> 00:29:24.150 good thing it is, because we wouldn't have the 00:29:24.150 --> 00:29:26.200 microelectronics age if it weren't for that. 00:29:26.200 --> 00:29:28.460 We couldn't have Teukolsky crystal growth and everything 00:29:28.460 --> 00:29:30.420 else that makes silicon dirt cheap. 00:29:30.420 --> 00:29:31.450 You know why it's dirt cheap? 00:29:31.450 --> 00:29:32.440 Because it's made from dirt. 00:29:32.440 --> 00:29:35.510 That's why it's dirt cheap. 00:29:35.510 --> 00:29:36.240 It's true. 00:29:36.240 --> 00:29:37.020 Here's aluminum. 00:29:37.020 --> 00:29:38.260 This is normal. 00:29:38.260 --> 00:29:41.440 This is the normal solid-liquid equilibrium. 00:29:41.440 --> 00:29:44.430 This is FCC metal, which is the closest packed. 00:29:44.430 --> 00:29:47.430 Axiomatically, the liquid must be less well-packed. 00:29:47.430 --> 00:29:48.030 All right? 00:29:48.030 --> 00:29:52.460 So this is dog bites man, this is man bites dog. 00:29:52.460 --> 00:29:54.320 This is the unusual one. 00:29:54.320 --> 00:29:54.770 OK. 00:29:54.770 --> 00:29:56.430 What else do we have? 00:29:56.430 --> 00:29:57.140 Nitrogen! 00:29:57.140 --> 00:29:58.620 Here's nitrogen. 00:29:58.620 --> 00:29:59.200 I drew this. 00:29:59.200 --> 00:30:01.120 So there's the 1 atmosphere line. 00:30:01.120 --> 00:30:03.750 Nitrogen boils at 77 Kelvin, and it 00:30:03.750 --> 00:30:05.680 freezes at about 63 Kelvin. 00:30:05.680 --> 00:30:08.320 And it's got the positive slope that you'd expect, and 00:30:08.320 --> 00:30:12.570 so solid nitrogen is denser then liquid nitrogen. 00:30:12.570 --> 00:30:15.010 And you can remember 77 Kelvin. 00:30:15.010 --> 00:30:16.560 You want to remember a few of these things. 00:30:16.560 --> 00:30:20.220 I wanted to point out to you that at atmospheric 00:30:20.220 --> 00:30:22.520 temperature, ambient temperature, you 00:30:22.520 --> 00:30:24.080 can remember 20-20. 00:30:24.080 --> 00:30:25.270 20-20 vision. 00:30:25.270 --> 00:30:28.850 So at 20 degrees C, it's roughly 20 millimeters of 00:30:28.850 --> 00:30:31.120 mercury, is the vapor pressure of water. 00:30:31.120 --> 00:30:33.240 It's not exactly true, but it's close enough. 00:30:33.240 --> 00:30:34.420 I think it's really 24. 00:30:34.420 --> 00:30:36.500 But 20-20 is nice to know. 00:30:36.500 --> 00:30:39.240 And what's the street address for MIT? 00:30:39.240 --> 00:30:42.490 77 Mass Ave. That's the boiling point of liquid 00:30:42.490 --> 00:30:45.390 nitrogen, 77 Kelvin. 00:30:45.390 --> 00:30:48.170 So I thought we'd do a few things here. 00:30:48.170 --> 00:30:54.320 And I'm going to show you a little bit of fun and games 00:30:54.320 --> 00:30:55.250 with liquid nitrogen. 00:30:55.250 --> 00:30:58.120 But first, I've been instructed I have to practice 00:30:58.120 --> 00:31:01.400 safe laboratory-- 00:31:01.400 --> 00:31:05.200 So I'm going to put on my lab coat. 00:31:05.200 --> 00:31:06.780 Yes. 00:31:06.780 --> 00:31:08.140 It's a nice lab coat. 00:31:08.140 --> 00:31:09.100 Mm-hm! 00:31:09.100 --> 00:31:10.370 Yeah, look. 00:31:10.370 --> 00:31:12.030 You want to know-- 00:31:12.030 --> 00:31:13.460 let's go back to this. 00:31:13.460 --> 00:31:14.820 They have to know where the-- this is not 00:31:14.820 --> 00:31:16.990 just any old lab coat. 00:31:16.990 --> 00:31:17.990 This is a nice lab coat. 00:31:17.990 --> 00:31:18.880 This is from France. 00:31:18.880 --> 00:31:21.060 It's from MAISON DUTECH. 00:31:21.060 --> 00:31:21.680 See? 00:31:21.680 --> 00:31:22.595 Notice the collar. 00:31:22.595 --> 00:31:25.460 It's not that typical, you know. 00:31:25.460 --> 00:31:26.560 MAISON DUTECH. 00:31:26.560 --> 00:31:27.420 OK. 00:31:27.420 --> 00:31:30.880 Let's go back to the phase diagram. 00:31:30.880 --> 00:31:37.140 So Dave Broderick is going to help us here. 00:31:37.140 --> 00:31:38.990 So we're going to have some fun. 00:31:38.990 --> 00:31:41.004 I'm going to put on a face shield so 00:31:41.004 --> 00:31:44.776 I don't blind myself. 00:31:44.776 --> 00:31:47.340 All right. 00:31:47.340 --> 00:31:50.240 Here we go. 00:31:50.240 --> 00:31:51.030 All right. 00:31:51.030 --> 00:31:52.700 So let's get some liquid nitrogen. 00:31:52.700 --> 00:31:53.950 Sounds different, huh? 00:31:55.970 --> 00:31:57.912 Sounds terrible for me. 00:31:57.912 --> 00:31:58.520 All right. 00:31:58.520 --> 00:32:02.080 So we've got some liquid nitrogen here, and I'll pour 00:32:02.080 --> 00:32:03.330 it into a Dewar. 00:32:20.140 --> 00:32:24.760 So what happens when you wet a sheet of paper with ink with 00:32:24.760 --> 00:32:25.650 liquid nitrogen? 00:32:25.650 --> 00:32:27.765 What kind of bonding is there in liquid nitrogen? 00:32:30.870 --> 00:32:31.370 Look. 00:32:31.370 --> 00:32:35.480 No running, no running. 00:32:35.480 --> 00:32:36.730 If it's liquid nitrogen. 00:32:39.715 --> 00:32:42.600 I tell you, everything you learn here is so valuable 00:32:42.600 --> 00:32:45.790 compared all the other stuff you learn here-- 00:32:45.790 --> 00:32:46.110 All right. 00:32:46.110 --> 00:32:48.450 So there's a couple of things. 00:32:48.450 --> 00:32:51.140 So let's look at glass transition temperature. 00:32:51.140 --> 00:32:52.320 So this is a latex glove. 00:32:52.320 --> 00:32:55.460 You can see it's above its glass transition temperature, 00:32:55.460 --> 00:32:58.150 and the cross-links are snapping it back. 00:32:58.150 --> 00:33:00.060 What I'm going to do, is take it down below its glass 00:33:00.060 --> 00:33:03.960 transition temperature, and turn it glassy and brittle. 00:33:15.600 --> 00:33:17.440 So that it's below the TG. 00:33:21.210 --> 00:33:23.260 Here's some paraffin. 00:33:23.260 --> 00:33:28.806 Paraffin, which is also a polymer here. 00:33:28.806 --> 00:33:31.470 Take the paper off. 00:33:31.470 --> 00:33:31.760 OK. 00:33:31.760 --> 00:33:32.570 So here's paraffin. 00:33:32.570 --> 00:33:32.880 Look. 00:33:32.880 --> 00:33:34.956 Look at the van der Waals bond. 00:33:34.956 --> 00:33:35.815 All right? 00:33:35.815 --> 00:33:38.480 This is van der Waals bond. 00:33:38.480 --> 00:33:40.730 Now we're going to go below the TG. 00:33:52.220 --> 00:33:53.350 It's liquid nitrogen! 00:33:53.350 --> 00:33:54.600 It doesn't matter. 00:34:00.100 --> 00:34:01.350 OK, you can hear it already. 00:34:04.900 --> 00:34:08.340 So it's now below the glass transition temperature. 00:34:08.340 --> 00:34:09.290 So what else have we got? 00:34:09.290 --> 00:34:10.970 Oh, you've heard of the glass flowers at Harvard? 00:34:10.970 --> 00:34:14.460 Well, we've got glass flowers here, so. 00:34:14.460 --> 00:34:17.520 Here's a rose. 00:34:17.520 --> 00:34:19.818 See, in the proteins, you know, it's above the-- you 00:34:19.818 --> 00:34:21.700 know, it's soft. 00:34:21.700 --> 00:34:25.250 But now, we're going to put the-- 00:34:25.250 --> 00:34:25.730 mm-hm. 00:34:25.730 --> 00:34:26.140 Here we go. 00:34:26.140 --> 00:34:27.390 You ready? 00:34:31.360 --> 00:34:31.780 Oh, come on. 00:34:31.780 --> 00:34:32.490 It's not a kitten. 00:34:32.490 --> 00:34:33.740 What's the matter? 00:34:39.200 --> 00:34:40.490 It's still burbling here. 00:34:40.490 --> 00:34:41.854 We have to wait until it's dead. 00:34:46.580 --> 00:34:47.830 This is for science. 00:34:54.420 --> 00:34:54.630 OK. 00:34:54.630 --> 00:34:59.480 Now it's below its glass transition temperature. 00:34:59.480 --> 00:35:00.117 Oh, I'm sorry, David. 00:35:00.117 --> 00:35:01.367 I should put this over on the other side. 00:35:05.130 --> 00:35:07.420 But maybe it's the red, or maybe it's 00:35:07.420 --> 00:35:08.250 because it's a rose. 00:35:08.250 --> 00:35:11.410 So here's the chrysanthemum. 00:35:11.410 --> 00:35:12.670 Today is your day. 00:35:15.490 --> 00:35:16.740 Let's go. 00:35:19.730 --> 00:35:20.980 Get this thing moving! 00:35:24.730 --> 00:35:25.980 Yeah. 00:35:31.090 --> 00:35:31.860 So there you have it. 00:35:31.860 --> 00:35:32.830 There you have it. 00:35:32.830 --> 00:35:33.940 I think that's-- 00:35:33.940 --> 00:35:42.742 oh, there's one, may we go back to the slide? 00:35:42.742 --> 00:35:44.710 Better put the gloves on for this. 00:35:44.710 --> 00:35:45.970 I'll have to write apology letters. 00:35:49.750 --> 00:35:49.990 OK. 00:35:49.990 --> 00:35:53.660 So we're going to do next, is we're going to look at phase 00:35:53.660 --> 00:35:54.470 equilibriums. 00:35:54.470 --> 00:35:56.890 There's the melting points and boiling point of oxygen, 00:35:56.890 --> 00:35:57.780 argon, and nitrogen. 00:35:57.780 --> 00:36:00.970 And what you notice is that nitrogen boils at a lower 00:36:00.970 --> 00:36:04.060 temperature then oxygen and argon. 00:36:04.060 --> 00:36:08.860 So what I'm going to do, is I'm going to pour some liquid 00:36:08.860 --> 00:36:10.930 nitrogen into this beaker. 00:36:10.930 --> 00:36:14.550 And then inside the graduated cylinder, I'm going to let it 00:36:14.550 --> 00:36:17.070 sit here, and we're going to condense air. 00:36:17.070 --> 00:36:18.680 And the result will be that we're going to start 00:36:18.680 --> 00:36:22.170 condensing liquid oxygen, and they'll be little bits of 00:36:22.170 --> 00:36:24.995 argon ice floating in liquid oxygen. 00:36:24.995 --> 00:36:28.850 And liquid oxygen is faintly blue, and it's paramagnetic, 00:36:28.850 --> 00:36:31.800 as you know, because it's got the unpaired electrons, which 00:36:31.800 --> 00:36:36.700 means that it will levitate in a magnetic field. 00:36:36.700 --> 00:36:39.120 I couldn't bring a big magnet in here, but we'll see if we 00:36:39.120 --> 00:36:40.000 can make some blue stuff. 00:36:40.000 --> 00:36:42.160 And it's foaming, because this would be like pouring water 00:36:42.160 --> 00:36:43.990 into something that's-- 00:36:43.990 --> 00:36:44.310 I don't know. 00:36:44.310 --> 00:36:45.340 300 degrees Centigrade. 00:36:45.340 --> 00:36:48.680 But eventually, the heat transfer gets low enough that 00:36:48.680 --> 00:36:52.845 you have stability here, and-- 00:36:52.845 --> 00:36:54.095 yeah. 00:37:04.990 --> 00:37:07.080 OK. 00:37:07.080 --> 00:37:08.870 Oh, that's terrific. 00:37:08.870 --> 00:37:09.120 OK. 00:37:09.120 --> 00:37:10.500 What else have we got? 00:37:10.500 --> 00:37:15.995 Let's go back to the slide. 00:37:15.995 --> 00:37:17.245 God, I hate this thing. 00:37:24.010 --> 00:37:24.310 OK. 00:37:24.310 --> 00:37:26.390 So you've been looking at that nitrogen. 00:37:26.390 --> 00:37:27.800 Let's look at what's next. 00:37:27.800 --> 00:37:28.090 Ah. 00:37:28.090 --> 00:37:31.280 Now if you solidify nitrogen here, you get a whole bunch of 00:37:31.280 --> 00:37:32.730 different polymorphs. 00:37:32.730 --> 00:37:34.030 Different crystal structures. 00:37:34.030 --> 00:37:36.630 So there are about five or six different crystallographic 00:37:36.630 --> 00:37:39.110 forms of solid nitrogen. 00:37:39.110 --> 00:37:41.640 For that, we'd have to bring liquid helium. 00:37:41.640 --> 00:37:43.000 4.2 Kelvin. 00:37:43.000 --> 00:37:45.210 Very cool stuff. 00:37:45.210 --> 00:37:46.510 Here's carbon dioxide. 00:37:46.510 --> 00:37:49.660 Now, it also has the positive slope, so solid 00:37:49.660 --> 00:37:50.760 will sink in liquid. 00:37:50.760 --> 00:37:52.610 But look, the interesting point here. 00:37:52.610 --> 00:37:55.400 The triple point is 5 atmospheres. 00:37:55.400 --> 00:37:58.750 At atmospheric pressure, you go directly from solid to gas. 00:37:58.750 --> 00:37:59.990 It sublimes. 00:37:59.990 --> 00:38:01.120 And that's advantageous. 00:38:01.120 --> 00:38:04.830 When we use carbon dioxide as a coolant, when it gives up 00:38:04.830 --> 00:38:08.520 its enthalpy to cool, it doesn't then turn into liquid. 00:38:08.520 --> 00:38:13.560 If you chill something with ice, with water ice, when it 00:38:13.560 --> 00:38:16.680 gives up its enthalpy, the object is 00:38:16.680 --> 00:38:18.460 now swimming in water. 00:38:18.460 --> 00:38:19.210 And that's no good. 00:38:19.210 --> 00:38:22.140 So hence we have the term dry ice, because we go directly 00:38:22.140 --> 00:38:26.310 from solid to vapor. 00:38:26.310 --> 00:38:27.460 And we want to prove this. 00:38:27.460 --> 00:38:33.660 So what we've got here is a big block of dry ice. 00:38:37.470 --> 00:38:40.850 So this is at minus 78 degrees Celsius, and it's 00:38:40.850 --> 00:38:42.040 still stable here. 00:38:42.040 --> 00:38:44.670 Well, it's subliming before your eyes. 00:38:44.670 --> 00:38:47.570 It's smaller than it was when we started the lecture. 00:38:47.570 --> 00:38:50.990 So what I'm going to do now-- 00:38:50.990 --> 00:38:55.170 oh, I'm not wearing that stuff. 00:38:55.170 --> 00:38:56.720 I guess I'd better. 00:38:56.720 --> 00:39:00.540 They're going to write me up on some log, 00:39:00.540 --> 00:39:01.960 teaching you bad practice. 00:39:01.960 --> 00:39:03.145 But anyways. 00:39:03.145 --> 00:39:03.670 All right. 00:39:03.670 --> 00:39:05.170 So what we're going to do, is we're going to test the 00:39:05.170 --> 00:39:08.130 proposal that this actually goes-- so I've got some water. 00:39:08.130 --> 00:39:10.920 Here, David, let's go out to the video. 00:39:10.920 --> 00:39:11.865 So let's take some water. 00:39:11.865 --> 00:39:13.680 I think we got water from France. 00:39:13.680 --> 00:39:14.700 Goes with the lab coat. 00:39:14.700 --> 00:39:16.335 This is Evian, OK? 00:39:25.260 --> 00:39:30.180 So I pour the Evian into the Florence flask. 00:39:30.180 --> 00:39:31.430 This is Florence. 00:39:37.310 --> 00:39:42.290 Florence is round, and the Erlenmeyer is the flat one. 00:39:42.290 --> 00:39:44.850 So let's move this guy. 00:39:44.850 --> 00:39:47.070 You're going in the backstage for a while. 00:39:47.070 --> 00:39:47.540 You just keep 00:39:47.540 --> 00:39:49.900 condensing All right. 00:39:49.900 --> 00:39:51.440 So now, this is here. 00:39:51.440 --> 00:39:53.230 Now what we're going to do, is we're going to put some dry 00:39:53.230 --> 00:39:54.870 ice in there, and see if we go directly 00:39:54.870 --> 00:39:59.150 from solid to a vapor. 00:39:59.150 --> 00:40:00.910 Take a chip off the old block, here. 00:40:17.450 --> 00:40:17.680 OK. 00:40:17.680 --> 00:40:19.590 So now you can see that it's going directly 00:40:19.590 --> 00:40:22.030 from solid to vapor. 00:40:22.030 --> 00:40:23.820 So that's carbon dioxide bubbles. 00:40:23.820 --> 00:40:27.480 And we assume that the phase diagrams is correct. 00:40:27.480 --> 00:40:29.980 I mean, another thing we could do, is-- 00:40:29.980 --> 00:40:33.342 I mean, I know what club soda tastes like. 00:40:33.342 --> 00:40:34.870 I could just test it, right? 00:40:40.120 --> 00:40:40.790 Yeah. 00:40:40.790 --> 00:40:44.590 It's carbon dioxide. 00:40:44.590 --> 00:40:45.840 Now! 00:40:47.580 --> 00:40:48.870 Here's the other thing. 00:40:48.870 --> 00:40:54.140 You know, Schweppes likes to pride itself on tiny bubbles. 00:40:54.140 --> 00:40:57.370 They have a tagline, Tiny Bubbles. 00:40:57.370 --> 00:40:57.630 Right? 00:40:57.630 --> 00:41:02.550 So here's Schweppes. 00:41:02.550 --> 00:41:05.930 And you can see Schweppes, with their 00:41:05.930 --> 00:41:07.410 wimpy little tiny bubbles. 00:41:07.410 --> 00:41:09.190 Can you get that, David? 00:41:09.190 --> 00:41:11.690 But we have, we have big bubbles. 00:41:19.100 --> 00:41:19.950 I mean, this is pure. 00:41:19.950 --> 00:41:21.080 You can't get any better than that. 00:41:21.080 --> 00:41:25.280 I got Evian water, and I got a block of carbon dioxide. 00:41:25.280 --> 00:41:27.080 I like making my own carbonated water. 00:41:27.080 --> 00:41:28.770 I've taken it to a new level. 00:41:28.770 --> 00:41:29.840 OK. 00:41:29.840 --> 00:41:31.930 What else do we have? 00:41:31.930 --> 00:41:33.890 Well, let's see if we made any liquid oxygen here. 00:41:40.840 --> 00:41:42.720 Try this. 00:41:42.720 --> 00:41:45.270 I don't know if we got anything here. 00:41:45.270 --> 00:41:45.670 Oh yeah! 00:41:45.670 --> 00:41:46.140 Oh, wow. 00:41:46.140 --> 00:41:47.390 Look. 00:41:52.070 --> 00:41:52.280 OK. 00:41:52.280 --> 00:41:53.890 So that liquid in there-- oh, I see. 00:41:53.890 --> 00:41:55.023 You've got a separate thing. 00:41:55.023 --> 00:41:56.382 I don't know if you can see. 00:42:00.140 --> 00:42:02.210 It's condensing. 00:42:02.210 --> 00:42:05.750 That liquid in there, that's liquid oxygen. 00:42:05.750 --> 00:42:09.100 I won't drink this. 00:42:09.100 --> 00:42:10.990 But I can inhale it. 00:42:10.990 --> 00:42:13.440 Pure oxygen. 00:42:13.440 --> 00:42:15.570 I could have a cigarette, and just put the 00:42:15.570 --> 00:42:18.310 cigarette in there. 00:42:18.310 --> 00:42:23.640 What happens if I put the lit cigarette into the oxygen? 00:42:23.640 --> 00:42:26.200 All that happens is that it burns quickly, that's all. 00:42:26.200 --> 00:42:27.130 There's no explosion. 00:42:27.130 --> 00:42:27.950 It burns quickly. 00:42:27.950 --> 00:42:30.990 If you walk into a room full of oxygen, all that happens is 00:42:30.990 --> 00:42:32.310 you'll singe your nose, that's all. 00:42:32.310 --> 00:42:33.410 There's no explosion. 00:42:33.410 --> 00:42:34.780 It's just oxygen. 00:42:34.780 --> 00:42:35.740 There's no fuel. 00:42:35.740 --> 00:42:38.550 The fuel is just in tobacco, and there's not much. 00:42:38.550 --> 00:42:39.220 It's not a problem. 00:42:39.220 --> 00:42:40.390 A room full of oxygen? 00:42:40.390 --> 00:42:41.390 Pfft! 00:42:41.390 --> 00:42:41.660 OK. 00:42:41.660 --> 00:42:46.501 Let's go back to the slides. 00:42:46.501 --> 00:42:48.780 What have we got here? 00:42:48.780 --> 00:42:51.940 We've got some examples of other phase diagrams. 00:42:51.940 --> 00:42:53.030 All right. 00:42:53.030 --> 00:42:54.820 Yeah. 00:42:54.820 --> 00:42:56.070 [MUSIC PLAYBACK: FROM 'PHANTOM OF THE OPERA'] 00:43:02.580 --> 00:43:03.840 PROFESSOR: Actually, it's quite tasty. 00:43:03.840 --> 00:43:04.340 All right. 00:43:04.340 --> 00:43:05.080 So. 00:43:05.080 --> 00:43:08.650 Now, here's zirconia. 00:43:08.650 --> 00:43:11.440 Now, here's the thing to know about zirconia. 00:43:11.440 --> 00:43:13.170 Look at all the different phases. 00:43:13.170 --> 00:43:15.565 And cubic zirconia is the one that has a high index of 00:43:15.565 --> 00:43:20.460 refraction, but it's stable only at temperatures exceeding 00:43:20.460 --> 00:43:24.160 2000 degrees C. So that's no good. 00:43:24.160 --> 00:43:27.700 So what I'm going to show you next day is that by changing 00:43:27.700 --> 00:43:32.290 the composition, and adding calcium oxide, we open up this 00:43:32.290 --> 00:43:35.250 zone here that's labeled cubic, and we get it stable 00:43:35.250 --> 00:43:36.940 all the way down to room temperature. 00:43:36.940 --> 00:43:39.920 It's an example of changing composition to get the 00:43:39.920 --> 00:43:43.160 stability of a phase that we want. 00:43:43.160 --> 00:43:44.130 This is carbon. 00:43:44.130 --> 00:43:46.700 So down here, the normal form, as we've learned earlier, the 00:43:46.700 --> 00:43:48.070 normal form is graphite. 00:43:48.070 --> 00:43:50.860 Diamond is formed at elevated temperatures and pressures. 00:43:50.860 --> 00:43:52.812 And this is liquid carbon. 00:43:52.812 --> 00:43:53.630 All right? 00:43:53.630 --> 00:43:57.270 Now, to make artificial diamond, you can try putting 00:43:57.270 --> 00:43:59.850 graphite in an anvil, and squeezing, and squeezing, and 00:43:59.850 --> 00:44:01.610 squeezing, and coming up into here. 00:44:01.610 --> 00:44:04.330 And then it becomes metastable, and then maybe, 00:44:04.330 --> 00:44:07.470 because the activation energy to jump from that sp3 00:44:07.470 --> 00:44:11.010 hybridized state to sp2 is so high, the diamond is stable. 00:44:11.010 --> 00:44:13.820 So you don't have to go running home to see if your 00:44:13.820 --> 00:44:16.300 diamond studs are now turning into graphite. 00:44:16.300 --> 00:44:16.700 They won't. 00:44:16.700 --> 00:44:18.700 Once you get into this zone, they'll stay. 00:44:18.700 --> 00:44:20.160 The activation energy is too high. 00:44:20.160 --> 00:44:23.850 You need more than 1/40 eV to do it, is necessary. 00:44:23.850 --> 00:44:26.820 But in the 1950s, General Electric, its Schenectady 00:44:26.820 --> 00:44:30.280 research labs, reasoned that because carbon is so soluble 00:44:30.280 --> 00:44:34.130 in iron, they could dissolve carbon in liquid iron, and 00:44:34.130 --> 00:44:38.880 then raise the pressure and temperature, and then change 00:44:38.880 --> 00:44:42.660 to exsolve and cause carbon to precipitate 00:44:42.660 --> 00:44:43.560 out of molten iron. 00:44:43.560 --> 00:44:45.340 That's the birth of artificial diamond. 00:44:45.340 --> 00:44:46.100 That's how they did it. 00:44:46.100 --> 00:44:50.268 Using this concept, but then dissolving it in molten iron. 00:44:50.268 --> 00:44:52.760 [MUSIC PLAYBACK: 'DIAMONDS ARE A GIRL'S BEST FRIEND'] 00:44:52.760 --> 00:44:53.700 PROFESSOR: I don't know how that got in there. 00:44:53.700 --> 00:44:55.450 All right. 00:44:55.450 --> 00:44:56.680 Here's one for mercury. 00:44:56.680 --> 00:44:59.430 I looked it up, using the tools that you've been taught 00:44:59.430 --> 00:45:01.300 here in 3.091. 00:45:01.300 --> 00:45:04.620 So this is a paper phase diagram for mercury. 00:45:04.620 --> 00:45:07.500 And physicists drive me nuts, because they plot temperature 00:45:07.500 --> 00:45:08.330 versus pressure. 00:45:08.330 --> 00:45:10.300 I want pressure versus temperature. 00:45:10.300 --> 00:45:12.060 So I just turned it around. 00:45:12.060 --> 00:45:14.070 And so here's the liquid line. 00:45:14.070 --> 00:45:17.950 So you know that liquid mercury is going to float on 00:45:17.950 --> 00:45:21.120 solid mercury, and there's a plurality of solid phases. 00:45:21.120 --> 00:45:24.230 And these are all different crystal structures. 00:45:24.230 --> 00:45:25.370 Now I've got a treat for you. 00:45:25.370 --> 00:45:28.590 I was in Barcelona several years ago, and I saw the 00:45:28.590 --> 00:45:32.920 mercury fountain that was made by Joan Miro in collaboration 00:45:32.920 --> 00:45:33.450 with Calder. 00:45:33.450 --> 00:45:36.630 Calder has the big sail outside of East Campus. 00:45:36.630 --> 00:45:39.670 So Calder collaborated with Miro, back in 00:45:39.670 --> 00:45:41.690 the '30s and '40s. 00:45:41.690 --> 00:45:45.480 And this is in honor of the miners of Almaden, where there 00:45:45.480 --> 00:45:46.950 are cinnabar mines. 00:45:46.950 --> 00:45:50.960 And the miners fought bravely against the Fascist forces of 00:45:50.960 --> 00:45:53.600 Franco, and Miro wanted to honor them. 00:45:53.600 --> 00:45:55.872 So here's their museum. 00:45:55.872 --> 00:45:58.150 It's a beautiful place up on top of an 00:45:58.150 --> 00:46:00.200 escarpment over Barcelona. 00:46:00.200 --> 00:46:03.710 And what I'm going to show you is a mercury fountain. 00:46:03.710 --> 00:46:05.160 [MUSIC PLAYBACK] 00:46:05.160 --> 00:46:06.410 This is liquid mercury. 00:46:08.940 --> 00:46:10.636 The speed has not been altered. 00:46:10.636 --> 00:46:14.540 This is a liquid at room temperature, density 13.5, 00:46:14.540 --> 00:46:15.980 metallic bonds. 00:46:15.980 --> 00:46:19.205 Look at it. 00:46:19.205 --> 00:46:20.848 Very high surface tension. 00:46:20.848 --> 00:46:22.098 Look at the way it shimmers. 00:46:24.310 --> 00:46:25.170 Look at this shot. 00:46:25.170 --> 00:46:26.360 This has not been altered. 00:46:26.360 --> 00:46:28.130 That's the way it pours into gravity field. 00:46:30.956 --> 00:46:32.210 It's really fantastic. 00:46:32.210 --> 00:46:34.250 And of course, mercury vapor is toxic, so the 00:46:34.250 --> 00:46:35.220 whole thing is in a-- 00:46:35.220 --> 00:46:36.180 [END MUSIC PLAYBACK] 00:46:36.180 --> 00:46:37.850 PROFESSOR: Oh, that's the-- 00:46:37.850 --> 00:46:40.340 I cut that snippet out of the documentary. 00:46:40.340 --> 00:46:41.460 OK, we don't want to see that. 00:46:41.460 --> 00:46:43.960 So they have the whole thing inside of a 00:46:43.960 --> 00:46:48.930 polymethylmethacrylate cage, to keep the mercury vapor from 00:46:48.930 --> 00:46:51.060 affecting the people that work in the museum. 00:46:51.060 --> 00:46:52.630 Here are some phase diagrams from hell. 00:46:52.630 --> 00:46:53.800 This is bismuth. 00:46:53.800 --> 00:46:55.110 And look at bismuth. 00:46:55.110 --> 00:46:57.830 Bismuth is like water, and like silicon. 00:46:57.830 --> 00:47:00.590 So the solid is less dense than the liquid. 00:47:00.590 --> 00:47:04.170 But look at all of these different phases. 00:47:04.170 --> 00:47:04.800 Here's sulfur. 00:47:04.800 --> 00:47:05.570 Sulfur is crazy. 00:47:05.570 --> 00:47:08.680 Look, phases in the solid phase, there's even phases in 00:47:08.680 --> 00:47:10.330 the liquid! 00:47:10.330 --> 00:47:12.130 Different phases. 00:47:12.130 --> 00:47:12.990 They're allotropes. 00:47:12.990 --> 00:47:13.810 Here's sulfur. 00:47:13.810 --> 00:47:16.865 Elemental sulfur, the disulfide, hexasulfide. 00:47:16.865 --> 00:47:19.890 It makes rings, it makes long chains. 00:47:19.890 --> 00:47:21.320 And these are called allotropes. 00:47:21.320 --> 00:47:23.950 They're different forms of the same element. 00:47:23.950 --> 00:47:29.520 So oxygen is O. There's the diatomic molecule. 00:47:29.520 --> 00:47:32.290 And the triatomic molecule, which is ozone, these are all 00:47:32.290 --> 00:47:33.540 allotropes of oxygen. 00:47:35.790 --> 00:47:36.720 What else do we have? 00:47:36.720 --> 00:47:37.030 OK. 00:47:37.030 --> 00:47:37.880 This is polymorphs. 00:47:37.880 --> 00:47:40.090 So this is alpha goes to beta. 00:47:40.090 --> 00:47:41.310 See, different crystal structures. 00:47:41.310 --> 00:47:43.720 You could see with your naked eye what's going on here. 00:47:43.720 --> 00:47:45.720 Different crystal structures. 00:47:45.720 --> 00:47:47.820 And then this goes to lambda, and then finally, they're 00:47:47.820 --> 00:47:48.850 pouring here. 00:47:48.850 --> 00:47:50.710 And if you get a very high cooling rate, and you've got 00:47:50.710 --> 00:47:52.670 those long chains, what happens? 00:47:52.670 --> 00:47:53.880 You don't form the crystal. 00:47:53.880 --> 00:47:55.280 You form the amorphous form. 00:47:55.280 --> 00:47:58.110 So they'll call this forming plastic sulfur. 00:47:58.110 --> 00:47:58.810 We know better. 00:47:58.810 --> 00:48:00.300 It's amorphous sulfur. 00:48:00.300 --> 00:48:01.550 It's not plastic sulfur. 00:48:03.580 --> 00:48:05.350 Here's water, a complete diagram. 00:48:05.350 --> 00:48:07.400 Now, this is in kilobars. 00:48:07.400 --> 00:48:09.260 So there's all the different phases of water. 00:48:09.260 --> 00:48:10.450 There's the negative line. 00:48:10.450 --> 00:48:12.450 That's the thing here. 00:48:12.450 --> 00:48:13.850 But at very, very high. 00:48:13.850 --> 00:48:15.350 Look at all the different phases of water. 00:48:15.350 --> 00:48:16.370 And they have numbers on them. 00:48:16.370 --> 00:48:17.940 If you read Kurt Vonnegut's Cat's 00:48:17.940 --> 00:48:19.650 Cradle, there's ice nine. 00:48:19.650 --> 00:48:23.720 You get that going, it freezes the whole world, right? 00:48:23.720 --> 00:48:25.560 But here's, I draw your attention on this one. 00:48:25.560 --> 00:48:26.850 You see this point here? 00:48:26.850 --> 00:48:29.110 This is ice seven. 00:48:29.110 --> 00:48:31.840 At 100 degrees C, it's solid. 00:48:31.840 --> 00:48:32.945 You need 25 kilobars. 00:48:32.945 --> 00:48:37.000 So we could go over to the lab, take some water, put 25 00:48:37.000 --> 00:48:41.600 kilobars on it, make solid ice at 100 degrees C. 00:48:41.600 --> 00:48:43.020 And it'll be stable. 00:48:43.020 --> 00:48:43.220 Look! 00:48:43.220 --> 00:48:44.500 This is minus 78. 00:48:44.500 --> 00:48:45.730 It's been here for a long time. 00:48:45.730 --> 00:48:49.060 So now I come into a cocktail party with this, I drop this 00:48:49.060 --> 00:48:54.150 ice cube into a glass of aqueous beverage, it sinks to 00:48:54.150 --> 00:48:59.460 the bottom, and the beverage heats up to the boiling point. 00:48:59.460 --> 00:49:02.350 That's what this is telling you! 00:49:02.350 --> 00:49:06.200 That'll get you popularity instantly. 00:49:06.200 --> 00:49:07.660 How did you do that? 00:49:07.660 --> 00:49:09.850 How did you do that? 00:49:09.850 --> 00:49:12.070 And up here is the supercritical fluid, the last 00:49:12.070 --> 00:49:13.600 thing we haven't said anything about. 00:49:13.600 --> 00:49:14.040 Look. 00:49:14.040 --> 00:49:16.410 If you take a gas, and you keep squeezing it and 00:49:16.410 --> 00:49:20.080 squeezing it, eventually the gas molecules are close enough 00:49:20.080 --> 00:49:22.470 together that they're indistinguishable from the 00:49:22.470 --> 00:49:23.590 liquid phase. 00:49:23.590 --> 00:49:26.700 Or if you start here, with the liquid, and you keep raising 00:49:26.700 --> 00:49:31.540 the temperature, the density goes lower and lower until the 00:49:31.540 --> 00:49:36.090 molecules are far enough apart that you can't tell this zone, 00:49:36.090 --> 00:49:41.270 whether it's a rarefied liquid or a highly compressed gas. 00:49:41.270 --> 00:49:42.860 The properties criss-cross. 00:49:42.860 --> 00:49:43.940 This is supercritical. 00:49:43.940 --> 00:49:49.840 It has liquid-like transport properties, and vapor-like 00:49:49.840 --> 00:49:50.780 chemical properties. 00:49:50.780 --> 00:49:54.150 So you can end up doing things that are very, very different. 00:49:54.150 --> 00:49:56.300 Now, I'm going to give you an example of decaffeinating 00:49:56.300 --> 00:49:59.020 coffee by taking the coffee, going up into the 00:49:59.020 --> 00:50:01.900 supercritical regime, which allows you to extract the 00:50:01.900 --> 00:50:04.340 caffeine, and not brew the coffee. 00:50:04.340 --> 00:50:07.070 So you want to just get the-- well, if you just heat it up, 00:50:07.070 --> 00:50:09.920 you'll make the coffee. 00:50:09.920 --> 00:50:10.930 So here's an example. 00:50:10.930 --> 00:50:12.360 It's called solvent extraction. 00:50:12.360 --> 00:50:14.910 Historically, this solvent was methylene chloride, which is 00:50:14.910 --> 00:50:16.900 also used as paint stripper. 00:50:16.900 --> 00:50:19.810 We don't do that anymore to coffee. 00:50:19.810 --> 00:50:21.580 They did in the '60s! 00:50:21.580 --> 00:50:22.020 They did. 00:50:22.020 --> 00:50:24.290 They also used trichloroethylene. 00:50:24.290 --> 00:50:26.750 It works really well to leech out the caffeine. 00:50:26.750 --> 00:50:29.780 How much is left in there for you to taste in your coffee? 00:50:29.780 --> 00:50:30.210 I don't know. 00:50:30.210 --> 00:50:34.320 Maybe that's why people were so excited in the '60s to 00:50:34.320 --> 00:50:36.160 drink their decaffeinated Sanka. 00:50:36.160 --> 00:50:36.610 I don't know. 00:50:36.610 --> 00:50:41.240 But anyway, so you take the green beans in carbon dioxide 00:50:41.240 --> 00:50:45.250 as supercritical, and drop the caffeine level, and then you 00:50:45.250 --> 00:50:49.110 play with temperature and pressure to go over the KSP. 00:50:49.110 --> 00:50:54.810 The caffeine salts out, and then you recycle the CO2. 00:50:54.810 --> 00:50:55.130 OK. 00:50:55.130 --> 00:50:56.190 I hope I've given you some 00:50:56.190 --> 00:50:58.700 introduction to phase diagrams. 00:50:58.700 --> 00:51:00.320 And we'll see you on Monday.