Analysis of thermal and electrical energy transport in Poco AXM-5Q1 graphite

Abstract

Thermal conductivity, thermal diffusivity, thermal expansion, electrical resistivity and heat capacity results which collectively encompass temperatures from 4 K to over 3000 K are presented on this graphite which is being considered as an international reference standard. Invoking the semi-continuum model for thermal energy transport, a theoretically predicted thermal conductivity curve is developed from 70 to 1000 K including crystal boundary and phonon-phonon scattering components. Graphite crystallite dimensions, the porosity/tortuosity factor and the modeling of crystallite interactions are shown to be fully reconcilable with theory and yield a predicted conductivity in very good agreement with the extensive measurements results. Above 1000 K and extending to 3000 K the experimental results from many different investigators show a clear hyperbolic temperature dependence in accord with expectations for a pure phonon conductor. Deficiencies in the theoretical modeling of energy transport in graphite are cited, and are shown to be relatively unimportant in the analysis conducted here. A quantitative relationship between electrical conductivity and the crystal boundary limited component of the thermal conductivity over a wide temperature range is demonstrated. However, as expected, no general relationship was found between electrical conductivity and the total thermal conductivity. A series of recommendations are made for additional experimental measurements on this graphite.