Gibbs energies of formation of chromium carbides

Abstract

The carbon potentials corresponding to the two-phase mixtures Cr + Cr₂₃C₆, Cr₂₃C₆ + Cr₇C₃, and Cr₇C₃ + Cr₃C₂ in the binary system Cr-C were measured in the temperature range 973 to 1173 K by using the methane-hydrogen gas equilibration technique. Special precautions were taken to prevent oxidation of the samples and to minimize thermal segregation in the gas phase. The standard Gibbs energies of formation of Cr₂₃C₆, Cr₇C₃, and Cr₃C₂ were derived from the measured carbon potentials. These values are compared with those reported in the literature. The Gibbs energies obtained in this study agree well with those obtained from solid-state cells incorporating CaF₂ and ThO₂(Y₂O₃) as solid electrolytes and sealed capsule isopiestic measurements reported in the literature.