Carbothermic Reduction of Alumina at 1823 K in the Presence of Molten Steel: a Sessile Drop Investigation

Abstract

The carbothermic reduction of alumina was investigated at 1823 K in the presence of molten steel in argon atmosphere for time periods up to 6 hours. A sessile-drop study was carried out to investigate the influence of operating parameters such as carbon/alumina ratio in the substrate, solute carbon level in the melt and reaction time. With molten steel acting both as a reducing agent and a metallic solvent, we report significant reduction reactions in the Al₂O₃–22.82 pct C/Fe (0.6 pct C) system, associated generation of CO gas and carbon pick-up by molten steel. The refractory substrate thickness was seen to decrease with time and the metal droplet started to flatten out and spread over the substrate after 5.5 hours. The chemical composition of metal deposited on the substrate was determined to be iron-aluminide; small levels of unreduced alumina and residual carbon were also observed. The carbon level in the metal droplet increased steadily to 1.5 wt pct during initial 3 hours and then decreased to 0.6 wt pct after 6 hours indicating carbon consumption; a small step increase in CO gas generation was also observed after 5.5 hours. While the metal droplet was still predominantly iron after 5 hours, it had completely transformed to iron aluminide after 6 hours of contact. The molten metal was also seen to penetrate deep in the substrate. These experimental results provide unambiguous evidence for a macroscopic carbothermic reduction of alumina occurring at 1823 K in the presence of molten steel and for the dissolution of product aluminium in molten steel.