THERMAL PROPAGATION IN CARBONS AND GRAPHITES AT VERY HIGH TEMPERATURES.
Rept. for Oct 65-Mar 67,
AEROSPACE CORP EL SEGUNDO CALIF LABS DIV
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Improved and new steady periodic heat flow methods for the direct measurement of the thermal diffusivity of carbons and graphites at very high temperatures have been recently developed. Their main features are techniques that overcome the difficulties caused by a radiative environment with thermal conductance much greater than that of the material under investigation. The results obtained with these methods indicate clearly that thermal propagation in carbons and graphites becomes essentially independent of temperature above 2000 K. This behavior contradicts the widely accepted claim that thermal conduction in carbons and graphites at high temperatures occurs via phonons. It is shown on the basis of existing band theories that all known facts about thermal and electrical transport phenomena at high temperatures can be reconciled by a bipolar electronic theory of the thermal conduction mechanism. In particular it is shown that, in this temperature region, the Wiedemann-Franz law holds with a Lorenz number of about 9ke to the 2nd power. Author