An Investigation of the Aluminum–oxygen–carbon System

Abstract

A differential thermal analysis technique was used to study the carbothermic reduction of aluminum oxide a t reduced pressures in the temperature range 1700-2200" K. The reduction was found to proceed through the intermediate oxycarbide A1404C, identified by previous workers, to the aluminum carbide. The A140aC and another oxycarbide, AlZOC, 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:Heats and free energies of reaction were found and standard heats and free energies of formation were calculated for AlzOC, A1404C, and A I L The values for A14C3 agreed with previously published results.The direct reaction did not occur. To account for the aluminum produced a t high temperatures, the reaction below was postulated:The calculated equilibrium pressure above this reaction agreed with experimental observations. ISTRODUCTIONIn the past few years, there has been a revival of interest in the production of aluminum by direct reduction (1, 2). Since a carbothermic reduction of aluminum oxide is involved in these processes, the present work was carried out to investigate the details of this reaction.Despite the industrial supremacy of the Hall-Heroult electrolytic process, there has been a sustained experimental interest in the aluminum-oxygen-carbon* system. Previous experiments on the system may be divided into two main groups. The first of these involved studies of the gas pressures existing above the system and paralleled the present investigation. The second, and more recent group, was a study of the compounds and phase relations occurring in the system, as determined by analyses of solidified melts of varying composition. In the latter group, a large number of compounds have been postulated by various workers (3, 4), but the existence of many of these has been disproved a t a later date. Foster, Long, and Hunter ( 5 ) have subjected the system to an extensive analysis in which two oxycarbides, AlpOC and A1404C, were found, as well as the known carbide,The existence of the two oxycarbides has been confirmed by Filonenko et al. (6, 7).* I n the text, the words graphite and carbon are used inte~changeably.

Rapid, energy-efficient synthesis of the layered carbide, Al4C3

“…40 Optical pyrometry offers a convenient, contactless method of measuring temperature without perturbing a microwave field. However, given the sealed tube reaction configuration shown in Figure 1, it proved impossible to obtain valid temperature values using this method.…”

“…40,41 The reasons for the preferential formation of oxides and oxycarbides under such conditions can perhaps be explained by the reaction processes that may occur in the presence of oxygen (Table 3). [40][41][42] The extremely high enthalpy and Gibbs free energy values for the oxide and oxycarbide phases strongly support the observed requirement for an oxygen-free environment. Moreover, the oxycarbide phase Al2OC has been observed to appear in carbon-rich environments 44 which may also be explained by the solid phase reaction given below (equation 2).…”

Volatilization of Aluminum Oxycarbides and of Alumina with Carbon in Reduction of Alumina

“…Unfortunately, no reliable experimental results have been reported so far, although Cox and Pidgeon (10) reported experimental values on the basis of a small change in DTA curve. As we discussed in I, A12OC can be stabilized by forming solid solutions with the isostructural compounds such as aluminum nitride and/or silicon carbide.…”

Carbothermic Reduction of Alumina at 1823 K: On the Role of Molten Iron and Reaction Mechanisms

“…[3][4][5] Thermodynamic studies on the system have revealed that the reduction of alumina is controlled by the formation of aluminium sub-oxide vapors. 6) Some studies have been reported on experimental investigations on the carbothermic reduction under vacuum conditions. 7,8) Frank et al have reported on the occurrence of carbothermic reduction of alumina in the temperature range 1 973 K to 2 073 K in the presence of a metallic solvent (Cu and Sn) at pressures between 0.08 to 0.20 atm.…”