Effect of Crystal Structure on the Anodic Oxidation of Nickel

The formation of Ni(OH)2 and NiOOH on different crystal planes of nickel, and of polycrystal l ine nickel, was studied in alkal ine solution. Oxide films of less than two monolayers were reduced potentiostatical ly, then current-potent ia l curves were measured in the range--200 to 1600 my at different rates of the l inear ly increasing potential. Electron diffraction and microscopy were used to develop a suitable exper imental procedure for dealing with bare and smooth nickel surfaces. The extent of oxide film formation in air on different planes was in the order (110) ~ (100) ~ (111). The re-activity on anodization, characterized by the potential at which the equivalent of one monolayer of hydroxide is formed, was in the same order. On continued oxidation the structure of the crystal surface is lost; subsequent reduction forms a strongly disordered surface. The results are discussed with regard to the mechanism of anodization, the extent of differences between crystal planes, and the conditions under which they are maintained or lost