Adsorption of Water on the Iron Surface with Reference to Corrosion

Moisture adsorption on the iron surface and its effect on corrosion were examined by quartz crystal microbalance (QCM) and thermal desorption spectroscopy. Reaction of water with the clean iron surface was examined by atom-probe. Amount of H2O adsorption increases sharply at 800% relative humidity (RH). Heat of adsorption is estimated to 11.2 kcal/ mol, which is close to the heat of vaporization of water and the critical number of monolayer, which exhibits the characteristics of bulk water is five. These results may suggest that adsorbed water forms localized water clusters rather than uniform film on the surface. The iron surface appears to be covered with OH in a form of Fe(OH) or Fe00H and water molecules are adsorbed on top. The oxidation rate also depends on RH and sharply increases at 80% RH.