Thermodynamic Properties of Ternary Refractory Carbides: I . Zirconium‐Niobium‐Carbon

Abstract

The nonstoichiometry of zirconium‐niobium‐carbide with the sodium‐chloride type structure, , was studied by measuring the activities of the components as a function of composition. Equations for the activities of the components as a function of composition were derived from statistical considerations, based on the pairwise interaction energies between various components, . Subscript . The energy terms, were determined by measuring the variation with composition of the ratio of the activities of the various components. The ratio of activities of the various components at one composition was determined in one experiment; thus, the usual errors in temperature measurement were eliminated. For this study a Bendix Time‐of‐Flight Mass Spectrometer was used. The samples were prepared by heating the required amounts of oxides and graphite in a high‐vacuum induction furnace. The metal‐metal interaction energy is not much different from that in the bcc metallic zirconium‐niobium system. The difference between the zirconium‐carbon and the niobium‐carbon interaction energies is linearly dependent on composition whereas , the carbon‐carbon interaction energy, can be expressed as .