Thermal conductance of graphite in relation to its defect structure

Apparatus developed for measuring thermal resistivities of well-oriented graphites in both a-axis and c-axis directions has been used over a range of temperatures from 90 to 350 °K. In graphites prepared by pyrolysis of methane, the proportion of defects has been varied by changing the conditions of deposition, and by annealing up to 3000 °C. Selected specimens were also irradiated with fast neutrons and were studied before and after annealing. To characterize the disorder in other ways, measurements of electrical resistivity and of thermoelectric power as a function of temperature were made in appropriate cases. Results are discussed with reference to mechanisms of thermal conductance in graphites.