CORROSION RESEARCH ROUND‐UP

Abstract

GREAT BRITAIN. Research at Cambridge University on aluminium. The oxidation of aluminium in dry and humid oxygen atmospheres has been investigated, using electrolytically polished aluminium single crystal surfaces. Anodic polarisation, electron diffraction and capacity were employed to identify and estimate the surface films. Film growth in dry oxygen is at first rapid and then slow, the growth rate being inverse logarithmic. A practical limit of approximately 30 Å is reached after several days' exposure. Water vapour increases film growth: after seven days' exposure the aluminium carries films which are about 10 Å thicker than those with dry oxygen. In the humid oxygen, film growth does not cease at a practical limit but continues at a slow rate after the initial period of rapid thickening. The growth law is direct logarithmic during the first tenth of exposure, and thereafter inverse. The films formed in both dry and humid oxygen were found by electron diffraction to be amorphous. Anisotropy in the growth rate of films of differently oriented metal phases has not been experimentally verified. No significant difference in the rate of oxidation was detected with three different crystal faces although the polarisation method is capable of measuring differences in thickness as small as 3 Å. Anisotropic growth is not a feature of thin films growing under the influence of strong fields, but only relatively thick films growing according to a parabolic relation. The electron diffraction patterns obtained from oxidised specimens (in dry and humid oxygen) consisted of two diffused haloes superimposed on top of the single crystal pattern from the aluminium substrate. The spacings of these haloes 2.45 and 1.38 Å correspond to the amorphous Al2O3 pattern.—(R. K. Hart, Proc. Roy. Soc., 1956, A236. (68–88).)

Citation

(1957), "CORROSION RESEARCH ROUND‐UP", Anti-Corrosion Methods and Materials, Vol. 4 No. 5, pp. 167-169. https://doi.org/10.1108/eb019327