AN INVESTIGATION OF THE ALUMINUM–OXYGEN–CARBON SYSTEM

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 Al4O4C, identified by previous workers, to the aluminum carbide. The Al4O4C and another oxycarbide, Al2OC, 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 Al2OC, Al4O4C, and Al4C3. The values for Al4C3 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.