PGS (Pyrolytic Graphite Sheet)

It's diamagnetic enough to hover on a rare-earth magnet.

Cheers

Phil Hobbs

Yeah, but can it core an apple?

I've never used it. The 8x conductivity is only in the plane of the sheet. Perpendicular to the sheet it's worse... you've got to get the heat into and out of the thing. At some thickness Al will still be better.

George H.

I used the Graphoil (tm) version of pyrolytic graphite as pump packing back in the '70s, when it was fairly new, and it works well for that application:

The corrugated ribbon form squishes down quite well to conform to irregular surfaces, or into the form of a packing ring, and the coefficient of friction against steel runs around 0.05 IIRC, as long as there is some moisture present; a few percent RH will do. The version intended to be used for sealing might have the spaces between graphite layers filled with water by exposure to high pressure steam as is normal for graphite lubricants; this makes the layers slide very easily and may account for the easy squish. (Graphite in the absence of water has a coefficient of friction against steel, other metals or itself of about 1.)

The lousy through-plane thermal conductivity (27 times worse than in- plane) probably has prevented wider adoption of pyrolitic graphite as a heat sink interface material, and I have to wonder how well the insulating properties of something with such a strong attraction to atmospheric water will hold up over time, for the insulating varieties. On the plus side, it should let parts with different thermal expansion slide easily, and the in-plane conductivity can help spread out small local hot spots somewhat, limited by small cross section if you use a thin enough layer for decent through conductivity.

Still good for packing though :-).

o 8x

We used graphite cloth as a thermal coupling material on both sides of our Peltier junctions in 1993. It was electrically conductive, which wasn't a p roblem in that application, squished down nicely, and seemed to do the job. I talked - implicitly - about the results in my 1996 millidegree temperatu re controller paper.

I haven't seen anything for sure, but I wouldn't be surprised if Apple is using it in the core of their iPhones or Macbooks. :-)

Tim

I've mused on it before; the data is something like:

- An equivalent piece of copper is 3 times thicker and 8 times heavier.

Considering the material isn't very thick to begin with (some mils), that's not a big deal to swing in most applications.

- An equivalent piece of copper is about 50 times cheaper.

When you need it, you need it, but... it's still very botique.

The insulating ones, I believe, are thanks to an insulating layer, not anything intrinsic to the material... guess what, even poorer Rth.

Tim