Oxidation behavior of metallurgical silicon slag under non-isothermal and isothermal conditions

Abstract

Metallurgical silicon slag is the by-product of metallic silicon industry. The utilization of silicon slag is very limited due to the absence of related researches. In this work, the oxidation behavior of metallurgical silicon slag was studied by means of phase variation under the non-isothermal and isothermal conditions. The crystal structure and phase composition of silicon slags were investigated by X-ray powder diffraction, simultaneous thermal analysis, scanning electron microscopy and thermogravimetry. During the oxidation process, the CO2 emission was progressively enhanced with increasing the oxidation temperature, and the exothermic oxidation primarily occurred above 700 A degrees C. The non-isothermal oxidation of silicon slag powder was a complicated process, involving the oxidation, crystal precipitation and disproportionation processes. The graphite phase was completely removed at 1000 A degrees C. The SiC and cristobalite phases greatly increased at 750 A degrees C and decreased with further increasing the oxidation temperature. For the isothermal oxidation, the Si and SiC phases generally reduced with increasing the soaking time. The cristobalite and tridymite phases increased with the oxidation time. The mass change in slag powders suggested that the isothermal oxidation process consisted of the initial redox reaction and subsequent oxidation reaction.