1998 Volume 47 Issue 7 Pages 476-483
The effect of water adsorption on the corrosion rate of aluminum thin film was measured by means of quartz crystal microbalance (QCM). The amount of water adsorbed on the surface was varied by contamination of the surface with varying amount of salt particles and relative humidity. The corrosion rate is closely related to the amount of adsorbed water, but independent of kinds of salt particles (NaCl, MgCl2·6H2O and (NH4)2SO4) used for contamination and temperature of corrosion rate measurements (20-40°C). Increasing difficulty of oxygen dissolution in the water thin film with temperature and inhibition of the anodic reaction by the corrosion products are suggested to be responsible for the present finding of little dependence of corrosion rate on temperature. The aggregation of water molecules is more efficiently taken place over the surfaces covered with the corrosion products than the uncorroded surfaces. This may be due to the changes of surface chemical properties and morphology rather than the hygorscopic effect of the corrosion products. An attempt has been made to quantitatively confirm the schematic relationship between the corrosion rate and the moisture film thickness proposed by Tomashov.