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Physics, Astronomy & Cosmology / How does Negative Thermal Expansion work?
« on: 02/03/2009 21:58:30 »
I was listening to a science podcast today and it stated that some substances shrink as they heat up. Apparently this is called negative thermal expansion. Eh? As any schoolboy knows, as a material heats up the atoms take on energy, vibrate more vigorously and expand into a larger space. Schoolboys also know that girls can’t throw and sometimes flap their arms about when they run, like….. well, like girls! But that’s the subject for another thread.
Silicon and Germanium apparently exhibit the characteristic of negative thermal expansion.
So my question is this:
How is negative thermal expansion possible?
Also, what would happen if you mixed a negative thermally conductive material with a positive one? Would you end up with a composite that doesn’t change size as it changes temperature? Or would it, on a microscopic level, expand at one molecule whilst contracting at it’s neighbouring molecule and then collapse into a pile of molecular size dust as soon as heat is applied?
Silicon and Germanium apparently exhibit the characteristic of negative thermal expansion.
So my question is this:
How is negative thermal expansion possible?
Also, what would happen if you mixed a negative thermally conductive material with a positive one? Would you end up with a composite that doesn’t change size as it changes temperature? Or would it, on a microscopic level, expand at one molecule whilst contracting at it’s neighbouring molecule and then collapse into a pile of molecular size dust as soon as heat is applied?