Determination of porosity of thin protective films on iron base materials and modelling of their development during aqueous corrosion

Corrosion properties of thin protective films on corroding substrates are dependent on the electrochemical properties of the substrate materials, the intrinsic corrosion properties of thin protective films and also on the films porosity. Therefore knowledge about the porosity is required in order to be able to control and optimise the deposition process. In this contribution a recently developed method to measure the porosity by means of an electrochemical technique is applied. As a model system thin iron films were deposited on silicon wafers and coated with amorphous carbon as a protective layer. The depositions were done by vacuum evaporation and ion assisted sputter deposition. Raman measurements, scanning electron microscopy, atomic force microscopy and electrochemical polarisation measurements were carried out to characterize the films. A model based on geometrical considerations is used to describe the development of the pores during corrosion. The measurement results show that the model is able to extract data on the pores