Formation of hexagonal η-MoC1−x phase at a temperature lower than 1660°C by solar radiation heating under presence of excess free carbon

Abstract

There are a number of Mo–C binary phase diagrams available and they are not necessarily in agreement with each other. Anyway, in none of them, presence of mono-carbide MoC is reported at temperatures between 1660 °C and 1150 °C. In this intermediate temperature range, sub-carbide Mo2C is identified as the only stable carbide phase in the binary Mo–C system even under presence of excess free carbon. However, in recent carbide synthesis work started from mixed powders of Mo and excess carbon under solar radiation heating, formation of hexagonal hypo-stoichiometric mono-carbide η-MoC1−x coexisting with sub-carbide Mo2C was detected. The target reaction temperature in the experiment was set to be 1600 °C and it took merely fractions of a second to heat from the ambient temperature to this target temperature in the used solar furnace. The possibility of formation of MoC is discussed with reference to the comparable experimental evidences obtained for W–C system also under solar heating condition with ultra-fast heating rate.