高温域におけるFeCr<SUB>2</SUB>O<SUB>4</SUB>およびMgCr<SUB>2</SUB>O<SUB>4</SUB>の炭素還元

Abstract

In relation to the smelting reduction of chromite ore, the mechanism of reduction of FeCr2O4 and MgCr2O4 with solid carbon was investigated at high temperatures from 1723 to 1923 K under an argon atmosphere. The rate of reduction was measured by means of thermogravimetry, and the formation of the reduction product was examined by microscopic observation.(1) With increase in particle size of FeCr2O4, the reduction rate decreased at low temperatures, but it was scarcely affected at high temperatures. During the reduction of the fine particle of FeCr2O4, the Fe-Cr-C alloy was formed around the graphite particle. In the case of the coarse particle, it was formed in the oxide. FeCr2O4 was essentially reduced by the combination of the gaseous reduction and the formation of Co, and at higher temperatures, the direct reduction by the carbon dissolved in the molten Fe-Cr-C alloy occurred simultaneously. The rate-determining step varied with the particle size of the samples and the experimental temperature.(2) When the particle size became extremely small, the reduction of MgCr2O4 was retarded as the result of the variation in the reaction mechanism. In the reduction of the fine particle of MgCr2O4, the graphite particle was coated with carbide. The rate determining step was the solid state diffusion through the cabide. The most of carbide was finely dispersed apart from the graphite particle at a low temperature, 1723 K. The reduction of the coarse particle of MgCr2O4 proceeded topochemically and was controled by the gas diffusion through the porous product layer.