CORROSION RESEARCH ROUND‐UP

Abstract

CHROMIUM Composition and properties of cathodic film in deposition. In a solution of chromic acid on the surface of a chromium cathode there may be a film of various kind. Cathodic films of a primary type arise in electrolysis of chromic acid in the presence of SO42− ions, have a macroscopic character, are more or less easily dissolved in the electrolyte without current, and facilitate reduction by chromic acid to metallic chromium. Oxide films (those of second(ary) type) are formed in electrolysis of chromic acid without sulphate ions, or without current through action of chromic acid on the surface of the cathode metal, have a microscopic character, are not dissolved in the electrolyte, and their presence does not facilitate reduction by chromic acid. It was found that the composition of the cathode films of the first type markedly changes with change in the composition of the solution and electrolysis conditions. Increase in current density and concentration of sulphuric acid, and also reduced concentration of chromic acid, increase the relative concentration of trivalent chromium and sulphate ions in the film. A connection was found between composition and strength (stability) of the cathodic films, on the one hand, and the rate of deposition of metallic chromium on the other. (Four references.)—Z. A. Solov'yeva et al., Zh. prikl. Khim., 1962, (8), 1806–1811.