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(ceramics) random walk approach to gases, liquids, or solids...

by asdf1
Tags: ceramics, gases, liquids, random, solids, walk
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asdf1
#1
Sep25-06, 08:57 AM
P: 741
For the random walk approach to gases, liquids, or solids, why isn't there a gradient? The atoms don't jump by themselves, right? They should have to feel forces to jump...
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Astronuc
#2
Sep25-06, 10:27 AM
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Quote Quote by asdf1
For the random walk approach to gases, liquids, or solids, why isn't there a gradient? The atoms don't jump by themselves, right? They should have to feel forces to jump...
Atoms vibrate - that is what temperature is - the kinetic energy of atoms. Think - Brownian motion.

And there is a gradient - the temperature gradient or concentration gradient. One can observe a concentration gradient by taking a drop of ink and dropping it in a liquid like water, and watching the ink disperse.

In the case of solids, the atoms are more or less fixed in position - that's what makes a solid solid. In liquids, the atoms/molecules are subject to interatomic/intermolecular forces, but the individual atoms/molecules can migrate. In gases, there is distance between the atoms/molecules and the interatomic/intermolecular forces are very low if existent.

Now in solids, there can be diffusion, but is very slow - orders of magnitude less than in liquids and gases. Hydrogen can diffuse in many metals. There is self-diffusion of atoms in a solid.

Think of the process of precipitation hardening of a metal.
asdf1
#3
Sep27-06, 08:24 AM
P: 741
Ok, I got it! Thank you very much!


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