A new method for accelerated atmospheric corrosion of anodized aluminum has been tested. The method consists of cycles of the three processes: introduction of a given amount of SO₂ gas into a test chamber, spray of test solutions of Cl^- and Cu²⁺ ions over corrosion test specimens, and drying of the sprayed specimens. Specimens corroded in this method had surface appearance similar to that of specimens in the atmospheric corrosion test. Pits appeared uniformly over the specimen surface and had certain diameters regardless of the location on the surface. It is concluded that this method has advantages over the CASS test.

View full abstract

Tannins and tannic acids may be grouped into hydrolyzable and condensable tannins. The former are highly effective for zinc corrosion inhibition. The effect of tannic acid purity on zinc corrosion inhibition was studied by treating zinc in hydrolyzable tannic acids of differing purities. The result showed that tannic acids with purities of 0.8 and higher in terms of ultraviolet absorption degree (where the tannic acid concentration was 20mg/l, the solvent was water, the cell distance was 1cm and λ=276nm) were particularly effective. The ratio of aromatic protons to alkyl protons of various tannins was determined by nuclear magnetic resonance method. The result showed that the ratio was remarkably greater for the high-purity hydrolyzable tannins than for condensable tannins and crude tannins. This reveals that the macromolecules, containing numerous aromatic rings, of the hydrolyzable tannins work in favor of zinc corrosion inhibition.

View full abstract

Measurements of limiting current densities at copper plating in acidified copper sulfate and copper fluoborate baths were conducted with a Hull Cell and a rotational electrode method. In the same cocentration of copper and an acid, the limiting current densities showed the same order of magnitude for copper sulfate solution and for copper fluoborate solutions. The diffusion coefficient of CuSO₄ calculated from the Levich equation had the same value as the calculated diffusion coefficient of Cu(BF₄)₂. These suggest that the reason why copper fluoborate bath is used for high speed copper plating is due not to the difference in diffusion coefficients of Cu(BF₄)₂ and CuSO₄ but to the higher copper concentrations obtained in the fluoborate bath. The paterns of “burnt” on a Hull Cell panel under unagitated conditions were explained in terms of the distribution of current densities over the panel in natural convection of the plating solution caused by electrolysis.

View full abstract