A conversion electron mössbauer spectroscopic and gravimetric study of the hydrolytic oxidation of iron fluoride hydrate surface layers

The oxidation of FeF 2-4H 2O surface layers in an atmosphere saturated with water vapour was studied by means of Mössbauer spectroscopy as well as gravimetry. The major rust product is identified as β-FeOOH, and the reaction is shown to proceed as a front from the layer-atmosphere interface towards the substrate. The ratio of the initial amount of fluoride on the surface to the final amount of rust produced was found to be constant, with the fluoride present in 1 mole of FcF 2-4H 2O reacting further to yield more than 5 moles of oxyhydroxide. This constant and non-stoichiometric yield is explained in terms of an acid regeneration cycle.