The Structures and Surface Composition of Chromate Conversion Coatings: An XPS and SEM Study

Abstract
In order to understand the mechanisms of adhesion of paints and lacquers to pretreated surfaces, topographical studies have been made of films formed on aluminium surfaces by ferricyanide accelerated Chromate pretreatment. Detailed XPS and bulk structural analyses were also made of a film with poor cohesive strength. Pretreatment resulted in a progressive smoothing of the original highly pitted surface remaining after initial alkali cleaning. The bulk of the film with poor cohesion was found to be comprised of layers of small (30–70 nm) particles with a surface chemical composition similar to that found for material in the surface of the film and typical of this type of pretreatment film. Similar but smaller particles are probably present on the surface although they have not been clearly resolved. Adhesion promotion is most likely to be due to the general smoothing of the surface or area increases due to the particulate nature of the surface. Cohesive failure of the films is more likely to be due to structural changes in the film than chemical compositional changes.

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