EVALUATION OF A STATISTICAL THERMODYNAMIC METHOD FOR CALCULATING COMPOSITION DEPENDENCE OF CHEMICAL POTENTIALS IN NONSTOICHIOMETRIC ZIRCONIUM CARBIDE

Mathematical expressions for carbon and zirconium activities in zirconium carbide are derived from a statistical thermodynamic model, on the assumption that nonstoichiometry is due to vacancies in the carbon sublattice while the zirconium sublattice remains filled. The energy term in the partition function is obtained by using a first‐ and second‐neighbor quasi‐chemical model. Values for the parameters used in the model are determined from available data as a function of composition. For C/Zr atom ratios between 0.59 and 0.85 the energy parameters are approximately composition‐independent, whereas in the composition range 0.85 to 0.99 they are strongly composition‐dependent. The vibrational partition functions of C and Zr in zirconium carbide are estimated and are shown to influence the value obtained for the model parameters. Copyright © 1969, Wiley Blackwell. All rights reserved