Characterization of thin iron phosphate films on cold-rolled steel surfaces by transmission electron microscopy and electron diffraction

Abstract

The determination of the structure and morphology of thin iron phosphate films obtained in an industrial phosphating process onto steel substrate materials of three different provenences was attempted by transmission electron microscopy and electron diffraction techniques. The structure was identified as primarily fine round-grained Fe 3(PO 4) 2·4H 2O together with microsurfaces containing mainly small crystals of γ-FeOOH and Fe 2O 3 and Fe 3O 4. The analysis of the microstructure showed that the growth of the film is markedly influenced by the substrate material. Also considered were the effects of thickness of the film and post-deposition annealing. The formation of the different mucrostructures is discussed.