Stability Range of MoC (HP2). II. Thermodynamic Properties of Generalized Lewis Acid-Base Intermetallics.

摘要

The gamma -MoC phase with the hexagonal WC structure was prepared without the presence of metal stabilizers at temperatures below 1000 deg C. This phase was found to be thermodynamically stable at low temperatures and decomposed to Mo deg C and graphite at 1400 K. Using equilibrium and thermodynamic data, the thermodynamic quantities of this phase were calculated as S sup 0298 /R = 4.41 +/- 0.3 and delta H sub 2980 /R = -3430 +/- 800 K. Part II. Oxide equilibration and solid-state galvanic cell experiments were used to study thermodynamic properties of binary Lewis acid-base stabilized transition metal alloys. The activity of vanadium was determined in alloys of vanadium with platinum group metals such as Rh, Pd and Ir at 1000 sup 0 C. The activities of titanium in titanium-iridium alloys and of niobium in Nb sub 2 Ir were determined at 1400 sup 0 C. The ternary phase diagram of V-Pd-O at 1000 sup 0 C was obtained. Based on the vanadium-palladium results, a partial titration curve of palladium by vanadium was constructed. The excess partial molar Gibbs free energy of vanadium at infinite dilution was found to be -36.4 kcal mol sup -1 at 1000 sup 0 C. The results of this study are in agreement with the predictions of Brewer's theory of transition metal alloy acid-base behavior. (ERA citation 13:036886)