Electrochemical and Ellipsometric Investigations of Passive Films Formed on Iron in Borate Solutions: I . The Kinetics of Film Growth on Iron at Constant Anodic Potentials

The kinetics of passive film formation on iron in borate buffer solution has been studied at different anodic potentials. The process of film growth has been found to occur in four distinct stages. About 80–90% of the total film thickness formed in 1h grows during the initial two stages which last for only 1–3s (depending upon potential). The electric field strength across the film is not constant but decreases with progressing film growth. The thickness of the film determined ellipsometrically is less than that calculated from the electric charge consumed. The process of anodic film formation is accompanied by the dissolution of iron which occurs over the whole range of potentials.