The diamond-graphite equilibrium calculation: The influence of a recent determination of the Gibbs energy difference

A recent determination of the difference in the Gibbs energies of diamond and graphite produced values close enough to those derived from calorimetric data to make discussion of the accuracy of previous calculations of the graphite-diamond equilibrium conditions and comparison with experimental conditions meaningful. Below 2000 K the observed equilibrium pressures are higher than those calculated but fall below them above 2000 K. Whereas the calculated volume changes at the transition and the weighted mean volume differences decrease with increasing temperature, the experimental equilibrium pressures correspond to a weighted mean volume difference which increases with temperature. One might be tempted to ascribe the discrepancy between calculation and experiment to the treatment of the compressibility of graphite at high temperatures and pressures. However, several different treatments of the compressibility gave similar equilibrium pressures and the discrepancy is largest at low temperatures where such a cause of error would be smallest. Copyright (C) 1996 Elsevier Science Ltd.