The Kinetics and Mechanism of Oxidation of Superpurity Aluminum in Dry Oxygen

A vacuum microbalance and furnace assembly was constructed and employed to determine the growth kinetics of oxide films on aluminum. Using electropolished foil samples of geometric area 80 cm2, and making corrections for spurious weight changes arising from thermal diffusion effects, film thickness changes as small as 0.3Aå could be reliably detected. In addition to kinetic data, the structure of representative oxide films was examined by electron microscopy. It was found that only "amorphous" oxide grew for about the first 10 hr at 454°C and for shorter periods at 478° and 505°C, the weight gain data being in good accord with an equation similar to that proposed by Mott and Cabrera for the growth of very thin oxide films, an approximate integrated form of which is sometimes referred to as the inverse logarithmic equation. The data could not be represented satisfactorily by either a parabolic oxidation law or a direct logarithmic law.