Aluminum corrosion in deaerated pure water

Abstract

The Amount of aluminum corrosion was critically measured in deoxidized pure water. It was indirectly calculated from the pressure of the hydrogen gas produced by the cathodic reaction. The accuracy of this device reached as high as 0.1 mg/m 2. The corrosion rate of A1N99 (99.99% aluminum) was then examined and compared with the images taken by both scanning electron microscope (SEM) and transmission electron microscope (TEM). In particular, images of the surface were taken by SEM and that of the cross section by TEM. From these comparisons, a new corrosion mechanism was proposed; 1) aluminum corrosion starts by the formation of small pits with a diameter of about 0.1 μm, 2) the number of these small pits increases and spreads over the entire surface. In addition, there is a time-lag between the increase of hydrogen gas pressure and the formation of corrosion products on the surface. The most likely reason for this time lag is that the Al ions require a long period of time to form stable oxide films.