Abstract
A rapid straining electrode technique has been applied to investigation of the initial process of anodic behavior on a newly created surface of pure nickel in high temperature and high pressure borate buffer solution up to 553 K. The analysis of the relation between the current density and the charge density shows that the repassivation process is divided into early and later stages. At the early stage, the newly created surface is covered with a monolayer of oxide film. The rate of this process follows a direct logarithmic law, showing neither potential nor temperature dependence. The mechanism of this stage is explained by the mutually-blocking pore model. At the later stage, the passive film grows following a parabolic law with the rate constant depending not only on temperature but also on potential. The rate of this process is determined by migration and diffusion of Ni2+ ions in the liquid phase under the potential and the concentration gradient through pores and other defects contained in the passive film.
