GIBBS ENERGIES OF FORMATION OF CHROMIUM CARBIDES

The carbon potentials corresponding to the two-phase mixtures Cr + Cr2 3C6, 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-h ydrogen 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. The se values are compared with those reported in the literature. The Gibb s energies obtained in this study agree well with those obtained from solid-state cells incorporating CaF2 and ThO2(Y2O3) as solid electroly tes and sealed capsule isopiestic measurements reported in the literat ure.