AN INVESTIGATION OF THE ALUMINUM–OXYGEN–CARBON SYSTEM

Abstract

A differential thermal analysis technique was used to study the carbothermic reduction of aluminum oxide at reduced pressures in the temperature range 1700–2200 °K. The reduction was found to proceed through the intermediate oxycarbide Al 4 O 4 C, identified by previous workers, to the aluminum carbide. The Al 4 O 4 C and another oxycarbide, Al 2 OC, were formed by a direct solid–solid reaction, rather than by formation of a gaseous aluminum suboxide and subsequent reaction with carbon as has been postulated.The carbon monoxide pressures over the following reactions were measured:[Formula: see text]Heats and free energies of reaction were found and standard heats and free energies of formation were calculated for Al 2 OC, Al 4 O 4 C, and Al 4 C 3 . The values for Al 4 C 3 agreed with previously published results.The direct reaction[Formula: see text]did not occur. To account for the aluminum produced at high temperatures, the reaction below was postulated:[Formula: see text]The calculated equilibrium pressure above this reaction agreed with experimental observations.