Carbothermic Reduction of MoO3 for Direct Alloying Process

The thermodynamics of Mo-O-C and Ca-Mo-O-C systems was studied in order to understand the carbothermic reduction of molybdenum trioxide, and kinetic studies were also carried out by means of thermogravimetric analysis under argon atmosphere with a heating rate of 10 °C/min. Subsequently, reaction products at various temperatures were identified by X-ray diffraction (XRD) and the results confirmed the previous thermodynamics analysis. Meanwhile, it was found that intermediate products MoO2 and CaMoO4 appeared in the process of carbothermic reduction of MoO3 with or without CaO, which were subsequently reduced to Mo or molybdenum carbide. An experimentally determined reaction mechanism was proposed and discussed. The reduction reaction of MoO3 with carbon could be divided into two stages. The first stage includes the direct reaction between MoO3 and carbon and the carbon gasification reaction. The second stage is the gas-solid reaction between CO and MoO2, and the diffusion of gases through the surface of MoO2 determines the overall reaction rate. The activation energies of the mixtures with or without CaO were estimated to be 56.6 and 52.9 kJ/mol, respectively.