Formation of COx species during the carbothermal reduction of oxides of Zr, Si, Ti, Cr, W, and Mo

The formation of CO and CO2 during the reduction of ZrO2, SiO2, TiO2, Cr2O3, WO3, and MoO3 by carbon was studied using two methods: (1) the carrier-gas hot-extraction method for oxygen determination in solids with the dissolution of carbon in the melt just before reduction, and (2) the usual carbothermal reduction method for carbide synthesis starting from oxide/carbon powder mixtures. In both the cases, significant amounts of CO2 were detected for WO, and especially for MoO3, in contrast to the other oxides. The kinetics of the carbothermal reduction of ZrO2, SiO2, TiO2, Cr2O3, WO3, and MoO3 were studied using a micro-scale method with the in situ analysis of the reaction gases CO and CO2. The progress of the oxide reduction reaction can be qualitatively and quantitatively measured at each moment of the experiments. Most of the results can be interpreted using the literature about oxide-specific mechanisms. In some cases, new aspects regarding the role of both species CO2 and CO were discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.