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[SQUEAKING]
[RUSTLING] [CLICKING]

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ISAAC METCALF: In
this video, we'll

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be discussing Goodie Bag
7, or crystalline defects.

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The objectives are to
visualize zero dimensional, one

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dimensional, and two
dimensional defects

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in crystalline materials.

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You'll need a double-sided
strip of adhesive,

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two Plexiglas panels, and
500 1/16th-inch metal beads.

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First, pull off
the protective film

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on the top of your
acrylic sheet.

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Take four pieces of
double-sided tape

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and put one piece on each of
the edges of the acrylic sheet.

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Then carefully put your balls
in the middle of the square made

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by the four pieces of tape.

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Finally remove the film on the
top of the other acrylic sheet

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and put it on top.

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When you're finished, you
should have a completed defect

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modeling kit.

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CAROLYN JONS: Now that
you've built your model,

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let's use it to visualize how
material processing impacts

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the number of defects
visible in a crystal.

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When looking at our
original crystal,

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you can see several defects.

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These are a vacancy,
line defect,

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and grain boundary defect.

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Material processing can lead
to both increases and decreases

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in the number of
defects in the material.

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A process that leads to an
increased number of defects

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is extrusion or rolling,
because when we extrude or roll

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a material, we force the atoms
to go into certain places

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and those aren't necessarily
the most energetically

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favorable states.

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Let's look at our
model to understand

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how material processing leads to
an increased number of defects.

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When we shake the model,
we're able to add defects

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to the system.

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As you can see now, our
model has an increased number

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of vacancies, line defects,
and grain boundary defects.

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Other material
processing methods

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allow for a decrease in
the number of vacancies.

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One possibility for
this is annealing.

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When we anneal, we
heat the material up,

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and then we cool it slowly and
allow the atoms to move back

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to their more favorable states.

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To illustrate annealing,
let's tap gently

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on the side of our model.

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As you can see, the number
of defects in our material

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has been substantially reduced.

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In this Goodie Bag, we
were able to visualize

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some of the defects
seen in many crystals,

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and we were also able to see
how processing conditions impact

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the number of
defects in a crystal.