Abstract
Oxidation of chemically polished high‐purity aluminum in dry oxygen, water vapor, and moist air at temperatures from 450° to 640C° is characterized by a near‐linear reaction rate to a weight gain of 3 µg/cm2, followed by a rate that decreases rapidly with further weight gain. Oxidation beyond the 5–7 µg/cm2 weight gain range is very slow. Oxidation is slightly faster in the moist atmospheres than in dry oxygen at temperatures above 550 °C. Oxidation of a commercial aluminum‐magnesium alloy (5052) in dry oxygen and in moist air is much faster than for high‐purity aluminum and proceeds to much higher weight gains. The rate does not conform to any recognized oxidation law, but it is more nearly parabolic than linear. The much higher weight gains obtained by other workers who used mechanically polished samples of both high‐purity aluminum and aluminum‐magnesium alloy are attributed to surface roughness. Electron diffraction examination of oxidized specimens show only eta alumina on the high‐purity metal and magnesium oxide on the aluminum‐magnesium alloy.