Surface modification of passive iron by alkyl-phosphonic acid layers

Phosphonate layer formation on passive iron surface has been investigated by electrochemical, conversion electron Mössbauer spectroscopy (CEMS) and atomic force microscopy (AFM) techniques. Electrochemical methods revealed that the prepassivation of iron surface results in stabilization of the phosphonate layer exhibiting favorable corrosion resistance. The rate of anodic dissolution is continuously decreasing due to the time-dependent formation of a protective phosphonate layer.The large Rct values of 1–20 MΩ cm2 indicate rather high blocking effect of metal dissolution by the phosphonate layer. The phosphonate layer formation has been also followed by the decrease of capacitance. CEMS investigations were carried out to evaluate the differences in the composition of the passive layer as a result of the phosphonate treatment. Mössbauer spectroscopy indicated the presence of iron phosphonate. Changes in morphology due to the phosphonate layer formation have been observed.