Measurements of membrane potentials across nickel, hydroxide precipitate membranes have been made to estimate the transport number of anions, the order of selectivity for anions, and the fixed charge concentration. The membranes show a high selectivity for anions; from the measurements of the membrane potentials, the transport number for anions evaluated to be 0.98 in sodium chloride, nitrate, perchlorate, and sulphate solutions. The order of the selectivity for anions determined with the biionic potentials is OH^->SO₄^2->Br^->I^->Cl^->NO₃^->ClO₄^-. This order of the selectivity is the same as that of the mobility in aqueous solutions, but the difference in the selectivity for these anions is greater in the membranes than in aqueous solutions. Nickel cations on nickel hydroxide precipitates constitute the fixed ion matrix characterizing the membranes as an anion exchanger, and its concentration is determined to be about 0.4g equiv./liter by comparing the experimental membrane potentials with the theoretical values according to the fixed charge theory of membranes.

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The effect of tarnish films on stress corrosion cracking behavior of pure copper and α-brass (Cu-10.1% Zn) was studied with respect to fracture strain of tarnish films formed in ammoniacal solutions of various concentrations (0.05-0.07M) at 70°C. Pure copper and α-brass were chosen since the former shows transgranular cracking whereas the latter does intergranular cracking. The onset of the fracture of tarnish film was detected from 1) the corrosion potential change upon straining at a strain rate of 1.0×10^-4min^-1 after 50hr immersion, and 2) the current change upon straining at the same strain rate after 23hr polarization at various potentials. The fracture strain was determined from the true strain at which the corrosion potential or the current starts to change. The fracture strain for the films on pure copper was found in the range of 1.1×10^-3-1.4×10^-3 and for the films on α-brass in the range of 1.3×10^-3-1.6×10^-3. The tarnish films on pure copper was observed to fracture within grains of substrate while those on α-brass predominantly at grain boundaries of substrate. The crack propagation rate and the time to failure estimated by tarnish rupture theory utilizing the experimentally determined values of the fracture strain, and the creep rate during SCC tests were in good agreement with those observed under constant load.

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