The oxidation of liquid alminium

Abstract

Structures and growth kinetics of oxide films formed on molten aluminium have been studied to provide. information in the context of melt losses and melt quality. Consideration of water vapour potentials at the boundaries of oxide films predicts that. in air-of normal humidity, a slightly hydrated transitional alumina (n - A1203) is stable at the oxide/atmosphere interface, and the dehydrated a- A1203 is stable at the metal/oxide interface. Structures observed in oxide films lifted from, the-liquid metal are consistent with this concept. The morphology of alpha-A1203 growing at the metal/oxide interface depends on the impurities incorporated within the oxide, and according to circumstances it can appear as degenerate dendritic shapes or plate like structures. The oxidation kinetics, in moist-oxygen, are characterised by a rapid initial rate during which n- A1203 plays a dominant but diminishing role, followed by much-slower kinetics after the alpha- Al2O3 subfilm is fully established and exercises rate control. Oxidation kinetics in dry. oxygen of samples obtained from high purity aluminium conform to theiparabolic growth law after an initial period during which linear kinetics are observed. The kinetics of samples obtained from commercial purity aluminium are much simpler and conform to the parabolic growth law.