Mechanism of aluminothermic reduction of MgO

Desulfurization and deoxidation of molten iron with magnesium vapor produced in-situ by aluminothermic reduction of magnesium oxide has been developed. In the present study, the mechanism of aluminothermic reduction of magnesium oxide by use of pellets composed of magnesium oxide and aluminum powders was discussed. SEM observation of the pellet at different reduction stages for various temperatures showed that fracture and disappearance of the alumina film on the aluminum particles were stimulated above 1473K, and thus the reduction of magnesium oxide was greatly accelerated. From in-situ observation of the aluminothermic reduction of magnesium oxide using a high temperature optical microscope (HTOM), it is found that the reduction proceeded after the penetration of molten aluminum into the magnesium oxide phase. The penetration began at 1273K, and it was accelerated above 1373K. The reduction took place violently at 1473K. SEM observation and EDS analysis of the cooled sample revealed that the penetration took place only through cracks of the alumina film. In-situ observation of the melting process of aluminum particles together with SEM observation of the cooled sample showed that the thermal stress could break up the alumina film and the outflow of molten aluminum did take place at the elevated temperature.