I was just wondering what other crystalline structures would be thermally conductive. So went looking around. Seems Ruby is meant to be very conductive at low temperatures, bad at high temperatures, 20C figures don't look good, didn't know whether "low temperatures" meant subzero, cryogenic, or ultra cryogenic. Anyhoo, for people with low temp setups it might be worth investigating.
Silicon Carbide, or synthetic moissanite as it is often known also may be worth investigating. It is very diamond like in structure, and is classed almost as an element in that the structure is very strong and regular more like an element than a compound. I am finding a very wide range of thermal conductivities for it. Jewellers and gemologists say "The thermal conductivity is so close to diamond that it's hard to tell them apart" other sources say it's between copper and aluminum, and others say that it's around about the value of nickel. So that's darn confusing. If it was near copper even, you'd think that even highly inaccurate thermal conductivity tests that jewellers might use would notice that diamond is 3 times better or so than SiC.
Anyhoo, there's also another crystalline material being touted for IC packaging called AlSiC which is up there near aluminum, dunno what AMD are using now, but they might like to think about that for their CPUs.
So a Ruby slice as a cold plate in a high pressure low temp peltier sandwich might be a viable idea, or might not.
Also an idea with CPUs with heatplates might be to get some real fine silicon carbide grinding powder, and instead of using thermal paste, just mash your sink into the heatspreader, grinding them into each other to get a kind of SiC and metal powder mix mating them. Might work good with a very light dab of boron bearing grease to help stick stuff together a bit.
Well whatever, there might be some interesting crystalline compounds out there to play with. Thermal conductivity charts seem hugely variable for off the wall materials though.
Here's one of them, showing the low value for SiC.
http://www.ai.mit.edu/people/tk/tks/tcon.html
Road Warrior