Anodic oxide films on nickel electrode in borate solutions

The effect of different concentrations of sodium borate, current densities, pH and temperature on the anodic oxidation of nickel was studied using galvanostatic polarization technique. The anodic potential-time curves showed four regions: the charging of the anodic double layer, an arrest corresponding to anodic dissolution and/or oxide film formation, linear rise in the potential due to the formation of barrier oxide film and finally deviation from linearity to reach steady-state potential value attributed to oxygen evolution reaction. The duration time of the arrest decreases with increasing current density and concentration of borate anion while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with increasing pH and temperature of the solution while the rate of oxide film formation decreases. Increasing the borate concentration and pH of the solution shifted the starting potential of the arrest towards more negative values. Linear relationships were obtained between the starting potential of the arrest and both borate concentration and pH.