CHLORIDE UPTAKE BY THE OXIDE FILMS ON SINGLE CRYSTAL AND POLYCRYSTALLINE ALUMINUM AS DETERMINED USING X-RAY ABSORPTON NEAR EDGE STRUCTURE

摘要

Two distinct chloride (Cl~-) species were detected on/in the passive oxides of polycrystalline aluminum (Al) and an Al single crystal with a <110> orientation which were anodically polarized below the stable pitting potential in Cl~- containing solutions. Chloride was found to be present as an adsorbed species at the surface of the oxide, as well as an incorporated species within the oxide. The two species of Cl~- were recorded by X-ray absorption near edge structure (XANES) using an electron yield detector. Electron yield XANES results indicate that adsorbed Cl" migrates from the solution/Al oxide interface into the passive Al oxide film, prior to stable pit initiation. Also, anodic polarization of aluminum single crystals show that the critical potentials for the onset of stable pitting (E_(pit)) of Al were dependent on the crystallographic orientation of the electrode surface, where E_(pit <111>) < E_(pit <100>) < E_(pit <110>P.