An XPS study of chromate pretreatment of aluminium

AbstractSurface analysis by X-ray photoelectron spectroscopy has been used, in conjunction with ion-beam etching, in order to study films deposited on aluminium surfaces before painting. Examples of both the chromate and the chromatephosphate series of pretreatments have been studied. The chromate film was found to consist mainly of hydrated chromium oxide, Cr2O3. XH2O (x=1 or 2), with a surface layer consisting of chromiumferricyanide or its decomposition products. The chromate-phosphate film consisted of mainly chromium phosphate, with smalle amounts of chromium oxide concentrated towards the metal/film interface. In both pretreatments fluorides were found at the interface between the film and the substrate. From the analysis, a general mechanism offilmgrowth is proposed.