MAE381 5 2010

MAE381 5 2010 - Chapter 5 Diffusion Skip Sec 5-7 5-8 and...

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Chapter 5 Diffusion Skip Sec. 5-7, 5-8 and 5-9.
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Separated particles can mix by randomly 'walking around'. This process is called Brownian motion, because Robert Brown was the first to see it with his microscope.
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Low and high entropy. For any state of any system there is a number that describes how messy it is, this number is called entropy. Any spontaneous process will increase a system's entropy (as stated by the second law).
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The second law of thermodynamics The entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.
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Diffusion of helium out of a balloon
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Ice melting - an example of entropy increasing
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The levels of atomic arrangement in materials: (a) Inert gases have no regular ordering of atoms. (b, c) Some materials, including steam and glass, have ordering only over a short distance (d) Metals and many other solids have a regular ordering of atoms that extends through the material.
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Introduction Difference between liquid-state and solid –state diffusion is the slower diffusion rate in the solid. Tight atomic structure of atoms has an impact on the diffusion of atoms or ions within the solid. The energy requirements to squeeze most atoms or ions through a perfect crystal structure are so high that diffusion is nearly impossible.
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What is needed to make solid-state diffusion practical? POINT DEFECTS!!!
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MAE381 5 2010 - Chapter 5 Diffusion Skip Sec 5-7 5-8 and...

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