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Theory of the effect of crystallite boundaries on the principal thermal conductivities of highly oriented graphite—The effect of the elastic constant C44

✍ Scribed by B.T. Kelly

Publisher
Elsevier Science
Year
1968
Tongue
English
Weight
538 KB
Volume
6
Category
Article
ISSN
0008-6223

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✦ Synopsis

The theory of the principal conductivities of highly oriented graphite as limited by crystal boundaries is re-examined using the recently measured value of the elastic constant C,,. The principal conductivities are calculated using the relaxation time approximation and assuming the presence of crystal boundaries parallel and perpendicular to the hexagonal axis defining scattering lengths L. and L, respectively. The lattice dynamics are those given by the semi-continuum model of Komatsu. It is shown that the introduction of the experimental value of C,, in the lattice dynamics leads to a satisfactory explanation of the "anomalous" temperature dependence of the basal conductivity. Parallel to the hexagonal axis it is shown that, as surmised previously, the out-of-plane acoustic mode contributes the major part of the conduction for reasonable ratios of La/L,. Experimental data on very perfect pyrolytic graphite is compared with the theory and a new comparison made of crystallite dimensions L, derived from electrica 1 and thermal property measurements.

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