Oxidation of Commercial Purity Aluminum Melts: An Experimental Study

Oxidation and dross formation is an undesirable, but unavoidable part of the production of aluminum. Past efforts to minimise dross formation through improved melt processing practices have been hindered by uncertainty in the fundamental behavior of how oxides grow on molten aluminum. The growth of oxide films formed on pure aluminum melts held at various temperatures and exposed to ambient air is investigated. Growth rates (i.e. mass/area as a function of time) were determined by skimming oxide films from laboratory-scale melt surfaces after various exposure times and then processing these films to separate oxide from metal. Collected oxide films were characterized using transmission electron microscopy (TEM) and electron diffraction techniques. γ-Al₂O₃ appears to be the dominant oxide species and no breakaway oxidation was observed even at 850°C/14h. The micro structural evolution of the films is discussed in light of the results and behavior implications of this work for industrial cast house situations are discussed.