An ellipsometric study of anodic passivation of nickel in borate buffer solution

Abstract

Ellipsometric and electrochemical measurements of the anodic passivation and secondary passivation films on nickel in borate buffer solution at pH 8·42 were made. The reference bare surface, obtained by cathodic reduction of electropolished nickel, gives the optical constants N 3 = 1·65−3·81 i for nickel. In the passivity region, where a little dissolution of nickel occurs, the surface film has the optical constants N 2 = 2·7−0·25 i and the film thickness as estimated by ellipsometry increases linearly with rise of the potential, from 4 to 13 Å, which is in fairly good agreement with the coulometrically estimated film thickness. In the oxygen evolution region, secondary passivation occurs with an abrupt increase in both optical constants and thickness of the surface film. The anodic passivation of nickel is compared with that of iron in terms of thickness of the surface film as a function of potential.