Kinetics of Formation of Molybdenum Carbide (Mo₂C) by Reaction between Carbon Monoxide and Molybdenite or Molybdenum

Abstract

Investigations have been conducted on the reactions between molybdenite (technical grade MoS₂) and molybdenum metal powders with carbon monoxide in the temperature range 1123 to 1298 K. The rates of both MoS₂+CO and Mo+CO reactions have been found to increase significantly with temperature. XRD examination of the reaction products reveal the formation of Mo₂C directly by the reduction-carburization of MoS₂. The said carbide is also observed to be the dominant product of molycarburization (Mo+CO) reaction. The MoS₂ conversion has been found to be a slow process, whose results fit into a linear rate law with a high activation energy value (230 kJ mol⁻¹). In contrast, the carburization of Mo powder has been observed to be a fast process, initially rapid upto about 30% conversion and subsequently progress in accordance with parabolic kinetics (low activation energy values of 76 and 33.5 kJ mol⁻¹, respectively for initial and parabolic stages). Since no elemental Mo has been detected in the products of the MoS₂+CO reaction, it is not possible to separate it from the subsequent in-situ molycarburization (Mo+CO) reaction. An indepth analyses of the findings indicate that the linear kinetics and the high activation energy value (230 kJ mol⁻¹) determined for the overall reduction-carburization of MoS₂ may pertain to the pre-requisite reaction (namely, MoS₂+2CO=Mo+2COS) itself.