| Abstract: | A Cameca Ion Analyser has been used to examine aluminium surfaces, covered by barrier-type anodic films up to 720 Å thick, after natural immersion for 480–1500 min or a brief period of anodic polarization in near-neutral I M potassium chloride solutions at 20°C. After natural immersion, there has apparently been slight film thinning and chloride is abundantly present on the film surface but there is no chloride measurable within the film material, nor is any residual chloride concentration in the tiny incipient pits, likely to be present at this stage, detectable. After anodic polarization, there is again evidence of a chloride peak on the film surface but no chloride within the film material itself. At the clearly detectable major pits, after passing through a surface chloride maximum, the chloride level is reduced until the inner oxide surface is reached, where a further chloride peak provides evidence for the pit undermining the anodic film. The results tend to support the pit initiation theory based on local attack at flaws in the preformed oxide film and provide no evidence for theories involving chloride ion entry into the film material per se. |
