Photoelectrochemical analysis of passive films formed on Ni and its alloys and its application to their corrosion behaviors

Abstract

A review is presented of the photoelectrochemical and Mott–Schottky analysis for the passive film formed on Ni and its alloys, and also of its application to clarifying the role of chloride ion and solution temperature in their corrosion behaviors. Photocurrent spectra for the passive film of Ni and its alloys, measured by the continuous illumination technique, can be resolved into spectral components, each of which originated from each compound comprising the passive film such as inner NiO and outer Ni(OH)2. The composition, structure, and electronic band structure of the passive films were characterized by comparing the band gap energy and the shape and peak position in the photocurrent spectra for the films with those for the thermally grown oxide. Mott–Schottky analysis revealed that the concentration of cation vacancy in p-type passive film of Ni is significantly increased either with addition of chloride ion or with raising solution temperature The significant increase in the concentration of cation vacancy is found to be main reason for the Cl− inducing passivity breakdown and also for the increase in corrosion rate with solution temperature. These experimental results are well corresponded to the role of Cl− in the passivity breakdown proposed by the point defect model.