Synthesis of Fine Mo₂C Powder from Prereduced Mo in Undiluted CH₄ Flow

Abstract

The carburization behavior of prereduced Mo was investigated in undiluted CH₄ flow at 900–1000 K. Prior to the experiments, equilibrium thermodynamic analysis was carried out in the Mo-C-H system. The products were characterized by mass measurement, x-ray diffraction and scanning electron microscopy techniques. A single Mo₂C phase was obtained within ~45 min, ~5 min, and ~2.5 min at 900 K, 950 K, and 1000 K, respectively, at CH₄ contents higher than the predicted ones. The reasons for this behavior were discussed in terms of CH₄ stability, open tube flow, and self-created atmosphere in the powder bed. The fractional conversion-time curves indicated that the carburization kinetics followed a linear rate law. The Mo₂C crystallite size (26–37 nm) and platelet thickness (50–100 nm) were found to be smaller than those of the parent Mo phase. These findings were attributable to the defects formed as a result of stresses associated with the reduction and the carburization.