Estimation of heat capacities of solid mixed oxides

Some empirical methods for the estimation of standard molar heat capacity (C°pm) of solid mixed oxides are reviewed and the reliability of the obtained data in phase equilibria calculations is examined. Following the comparison of predicted values of C°pm(298.15 K) with more than 300 experimental data the most widely used Neumann–Kopp rule (NKR) is found to be very universal but in some cases the mean deviation of 3.3% is too high, giving rise to a relatively large error in equilibrium calculation results. On the other hand, the method based on binary oxide contributions proposed by Berman and Brown [Contrib. Mineral. Petrol. 89 (1985) 168] for the estimation of temperature dependencies C°pm(T) of silicates and other minerals formed by Al2O3, CaO, FeO, Fe2O3, K2O, MgO, Na2O, SiO2 and TiO2 is less general, but more accurate. In comparison with the NKR, the most pronounced drawback of this method is the necessity to know the experimental values of C°pm for a set of mixed oxides, so that the individual contributions of constituent binary oxides can be evaluated.