Thermal expansion of graphite revisited

Abstract

A heuristic approach to the analysis of the thermal expansion of materials is proposed in the form of an infinitely differentiable analytical expression for the coefficient of linear thermal expansion, which is consistent with the requisites imposed by Thermodynamics as T→0+ and also exhibits the correct asymptotic behavior in the limit of high temperatures. This expression is compared to a previous model based on the summation of Einstein’s terms, both models being applied in a multi-objective fitting taking as input data lattice parameters and linear coefficients of thermal expansion of graphite over a broad temperature range from near absolute zero up to above 3000 K. Knowledge of the temperature dependence of the coefficient of thermal expansion allowed estimating the effect of pressure on the molar heat capacity of graphite, for which ∂Cp/∂pT<0 until becoming mostly insensitive to pressure above about 1500 K.