|Sep25-06, 08:57 AM||#1|
(ceramics) random walk approach to gases, liquids, or solids...
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...
|Sep25-06, 10:27 AM||#2|
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.
|Sep27-06, 08:24 AM||#3|
Ok, I got it! Thank you very much!
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