Solid-state reduction of chromium oxide by methane-containing gas

Abstract

Reduction of chromium oxide, Cr₂O₃, was investigated in a fixed bed laboratory reactor in the temperature range 900 °C to 1200 °C using CH₄-H₂-Ar gas mixture. The extent and rate of reduction as functions of gas composition and temperature were determined by on-line off-gas analysis using a mass spectrometer. Samples at different stages of reduction were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The chromium oxide was reduced to chromium carbide Cr₃C₂ with a degree of reduction close to 100 pct. The rate of reduction increased with temperature and methane content in the reducing gas. Carbon monoxide, added to the reducing gas, strongly retarded the rate of Cr₂O₃ reduction. The hydrogen content had a slight effect on the reduction rate. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas—15 to 50 (relative to graphite).