STRESSES PRODUCED BY THE ANODIC-OXIDATION OF NICKEL

Mechanical stresses produced during the anodic oxidation of nickel in 0.1 M H2SO4 with and without 500 ppm Cl- were measured by a beam deflection technique. Potential sweep, potential step and pit initiation experiments were performed. During sweeps the active-passive transition is marked by a sharp compressive stress of 1-3 GPa during the formation of the first monolayer. Oxides formed in Cl-containing solutions exhibited higher stresses (3-9 GPa). Potential steps in the passive region produced stress changes consistent with a change of volume due to valence changes within the oxide. No correlation is found between the initiation of pitting and the build-up or relief of stresses; however, very localized stress variations are not ruled out.