Kinetic Studies on Hydrogen Reduction of MoO₃ and Morphological Analysis of Reduced Mo Powder

Abstract

The studies on hydrogen reduction of MoO₃ indicated two main stages, namely, MoO₃ to MoO₂ and MoO₂ to Mo. In both stages, temperature and time of reduction progressively increased on diluting hydrogen from 100 to 10 pct. Detailed kinetic analysis of the MoO₂ to Mo stage was conducted by carrying out isothermal reduction between 625 °C and 900 °C by pure hydrogen. The kinetic equation was found to be $g{\left( \alpha \right)} = {\left[ { - \ln {\left( {1 - \alpha } \right)}} \right]}^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 n}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$n$}}} = {\text{k}}t$, with n ranging from 1.49 to 2.13. The rate constant k obeyed the Arrhenius temperature dependence with the associated activation energy of 136 kJ mol⁻¹. The X-ray diffraction (XRD) analysis of the product confirmed the phases predicted by thermal analysis. The scanning electron microscope (SEM) analysis of molybdenum powder revealed the presence of a greater number of pores and cracks in the individual particles produced at lower reduction temperatures and the tendency of acquiring spherical morphology with increasing reduction temperature. Based on the studies conducted, the optimum conditions for MoO₃ to Mo reduction were predicted.