Microstructure Development of Aluminum Oxide: Graphite Mixture During Carbothermic Reduction

Abstract

Reactions in the system Al‐0‐C are discussed. Reaction conditions which produce an α‐alumina body having a <70%‐dense bulk region coated with an impervious, ∼100‐μm thick surface layer are described. The development of the unique composite microstructure is attributed to reactions which serve to coarsen internal grains by vapor‐phase transport of volatile aluminum suboxides and, thereby, reduce firing shrinkage. Proper control of the furnace atmosphere is necessary to produce the thin, dense surface layer. The effect of varying the carbodalumina molar ratio on linear firing shrinkage, tired density, and weight loss was examined. In addition, the effect of oxygen partial pressure on the oxidation of carbon and the formation of an intermediate reaction product, Al 4 O 4 C, was examined.