Thermal conductivity (ceramics)

So back to anodized aluminum. Can I treat a 2 mil anodized layer like it's 2 mils of Al2O3?

(I may have to rethink the whole design...)

George H.

Not quite :-). Diamond is carbon with 4 covalent bonds per atom (the shortest and strongest chemical bonds known) with a nominal cubic structure, graphite is carbon with 3 covalent bonds per atom and a nominal hexagonal structure. Either of these materials can be found in amorphous, polycrystalline of single crystal forms.

When thinking of amorphous materials like glass there is a tendency to think of them as a distinct state of matter; but if you look close enough, on the scale of a few atoms, you will see the same sort of bonds as in crystalline forms of the same substance, but more strained on average. If an amorphous material is heated near melting, the scale of crystalline order will slowly grow from a few atoms in an ordered group to large, distinct crystals; clearly polycrystalline, but there is no distinct phase change involved, just a continuum of increasing scale of order and decreasing average bond strain.

Neither amorphous nor polycrystalline properly describe coal, it is somewhere in between, but it is almost entirely graphite type bonds rather than diamond bonds. When the scale of order of these graphite bonds is so small and randomly ordered that material properties are essentially isotropic, the material is generally referred to as amorphous carbon. Coal can vary widely in it's scale of order, from glass-like through large graphite flakes. Most engineered carbon materials are derived from petroleum or natural gas, not coal, due to the inconsistency and high level of impurities found in coal.

What is it good for? It's not an electrical insulator. Adding any interface layer, even solid diamond, still adds theta. A little silicone grease would be better in most situations.

It might be OK for interfacing rough surfaces.

Isotopically pure crystalline diamond. Kinda hard to machine.

How about stealth aircraft models, that are actually "stealthy"? :-) Not sure about good for anything, but off the wall topic...

-bill

Sure... but it beats the snot outta 1 mil of Kapton.

George H.

Hehe.

I'm thinking of vapor deposited kind. But... yes, that too.

Jon

Looks darned good. I just hope they make the stuff safely. Machining beryllium metal is dangerous (but it has useful thermal expansion and heat dissipation characteristics.) I've used it before in places where the expansion needed to be very low. But hiring machinists for that is a different story.

Jon

AlN is almost as good thermally, but not toxic.

BeO has the best thermal conductivity/dielectric constant ratio, except for diamond.

... attched by a few mils of acrylic adhesive.

A thread that ends happily?

My only contact with Beryllium was ordering a 6 inch diameter dome from Brush-Wellman. It was the end of the vacuum chamber for an electron beam... right above the beam dump. Only 5mil thick at the center.

George H.

We had a generator from HP that advertised the Be substrate on the output diver with a warning inside the case. Our industrial safety people just about had a cow. They generators were all pulled until they got a statement from HP that they were safe to use. No one said they were bright (the security people there would only put a lock on one door to the lab because two would only be half as secure).