Effect of applied potential steps on stresses of anodic oxide film on nickel

Stresses in anodic oxide films on nickel thin film/glass electrodes in pH 8.4 borate solution were investigated by a bending beam method. Tensile stresses were always measured during the formation of the oxide film, representing the significant contribution of cation transport to the growth of the oxide film. The downward and upward potential steps in the passive and hydrogen evolution potential ranges after passive film formation produced instantaneous changes in stress toward the compressive and tensile direction, respectively. This was attributed to the changes of cation valence and ratio of OH-/O2- in the hydrated passive film, NiO1+x . yH(2)O. The large difference in stress with and without the oxide film suggested that most of the stresses generated during the application of potential steps reside in the oxide film. A linear relationship between step changes in stress and relative concentration of absorbed hydrogen was found from the current and stress transients. The similarity of the magnitude of stress with potential steps between the oxide films formed in the passive and transpassive potential ranges, respectively, are discussed in terms of the structural characteristic of transpassive film consisting of a porous and a thick layer. (C) 2003 The Electrochemical Society.