Volatilization and condensation behavior of magnesium vapor during magnesium production via a silicothermic process with magnesite

Abstract

The condensation behavior of magnesium vapor produced by metal Mg or pellets for magnesium production is investigated at heat source temperatures of 1173–1473 K under vacuum. The possibility of reduction of magnesite in vacuum was analyzed by means of thermodynamics. The results indicate that the thermal motion of magnesium is violent, and the volatilization rate increased with high heat source temperature, the results accord with Maxwell's velocity distribution law. Magnesium vapor condensation products were obtained with flake and powder macromorphologies, where the flake products accounted for more than 80% (in mass). Scanning electron microscopic analysis revealed that the main factor affecting the magnesium vapor condensed particles was the vapor pressure, which was determined by temperature and reaction. The end condensation temperature was between 528.1 and 637.1 K when the heat source temperature was 1173–1473 K. Increasing the temperature gradient decreases the condensation temperature range. X-ray diffraction results showed that the magnesium condensation products were more crystalline at lower vapor pressure and a small temperature gradient. The presence of Ca2SiO4 in the reduction slag indicated the occurrence of the reduction reaction. The experimental results from pellets for magnesium production were consistent with those involving Mg metal.