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document updated 12 years ago, on Feb 23, 2012

Using graphite powder as a heat moderator has several benefits:

it's cheaper than most other materials that have a high thermal conductivity (that table can be sorted by conductivity)
being granular, it can mold to the shape you need, and fill cracks, which increases thermal conductivity

It has some downsides:

it's *not* as conductive as metal, or metal powder (though it's cheaper)

And some things that are neutral, but might be irksome:

It is highly anisotropic — It has a MUCH higher thermal conductivity in one direction than the other. Thus, powders *do* have lower thermal conductivity than if they were heat-pressed/sintered into shape.

What is the thermal conductivity of powdered graphite?

Most statistics given online assume solid graphite, and thus assume you use graphite in its proper orientation. With powdered/flaked graphite, this isn't the case. So this data is more difficult to come by.

110 W/m K (search for "scrap", though this is for powder that has since been pressed into a hard shape)
Graphite-based thermal grease has a thermal conductivity of 0.8 - 10 W/mK. This is clearly particulate graphite, though the grease may change the thermal properties as well.

How is industrial graphite pressed?

See here, particularly the bit about "graphitization". To get the carbon to align, you need temperatures of 2500-3000°C. So, this plainly isn't something you can do at home.