Mechanism of carbothermic reduction of chromium oxide

The isothermal experiment of carbothermic reduction of chromium oxide was carried out. The reduction rate increased by increasing temperature, using a moderate carrier gas flow rate and the fine graphite particles. XRD analysis revealed that Cr3C2, Cr7C3, Cr23C6 and Cr were formed in turn as the reaction products at 1 673 K. The relation among the products, reduction temperature and time was summarized from the XRD results at the temperature range from 1 373 to 1 673 K. It is confirmed that the reduction contains various kinds of reactions, such as direct reduction, indirect reduction of chromium oxide, the carbon solution loss reaction and the reaction of chromium carbide with carbon dioxide. At the initial stage of reduction, the direct reduction dominates the reduction rate. At the later stage of reduction, because of the chromium carbide layer formed on the surface of graphite particles and rather slow reduction rate, the rate-controlling step is deduced to be CO and CO2 gas diffusion through the layer of reduction products.