XPS studies of a ferricyanide accelerated chromate paint pretreatment film on an aluminium surface

An XPS analysis of a ferricyanide accelerated chromate paint pretreatment film found iron in the form of both a ferricyanide and a ferrocyanide ion. Chromium occurred in at least two different chemical environments, one of which was as a hydrated oxide. Aluminium and fluorine probably occurred together although the analysis was not conclusive in this respect. More positive evidence is available elsewhere. The behaviour of the elements on ion etching was consistent with a model of the film comprised mainly of hydrated chromium oxide microcrystallites covered with a monolayer of ferricyanides. Escape depth calculations and correlation of semiquantitative analysis with chemical and energy-dispersive analyses of the film were also consistent with this model. Adsorption of ferricyanides on the surface of the precipitating particles of the growing film provides an explanation for their role as accelerators of film growth.