Evidence for a molecular intermediate during the oxidation of aluminum by water

The interaction of H2O with the Al surface plays an important role in the atmospheric and aqueous corrosion of that metal. In order to clarify the oxidation mechanism involved in this process, we studied the initial stages of H2O adsorption upon the Al(100) surface using the techniques of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and high resolution electron energy loss spectroscopy. The experiments were performed at a substrate temperature of 100 K in an attempt to stabilize any short-lived intermediate species involved in the oxidation process. The experiments show that the initial H2O interaction with the clean Al(100) surface at 100 K forms a molecular H2O species. Further H2O exposure results in the condensation of H2O multilayers (ice) upon this surface species. Heating the sample to 300 K desorbs the ice layer and forms an oxide similar to that formed in a 300 K H2O/Al(100) oxidation; no trace of H2O is detected on this surface but an oxide-stabilized OH species is present.