The corrosion of Cu-base alloys in water containing 1-1, 000ppm NH₃ has been studied in view of the potential corrosion problems in the condenser tubes of thermal power plants. The results are as follows:
1) The corrosion resistance was in the increasing order of copper, aluminium brass, 9:1 cupronickel and 7:3 cupronickel. The dissolution rate of copper was high at higher concentrations of NH₃, i.e., 1, 000ppm and low at lower concentrations, i. e., 1-10ppm.
2) The corrosion resistance presumably depends upon the inherent nature of the surface films, which can be explained in terms of the pH-potential diagram.
3) Steel in contact with the Cu-base alloys gives negligible accelerating effect in spite of the fact that the former has more noble potential in the concentration region of 1, 000-10, 000ppm NH₃. The self-corrosion of the latters predominates in this region.

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Studies have been carried out on the characteristics of “Pseudo-Rust” formed by the neutralization reaction between metallic chloride (FeCl₂, FeCl₃ and CuCl₂) and sodium hydroxide solutions placed on each side of analytical filter paper used as a diaphragm. The pseudo-rust precipitated at the filter paper-metallic solution interface in agreement with the previous result where an anion exchange membrane was employed. X-ray diffraction identified metallic iron and copper, their oxides, oxyhydroxides and hydroxides. The distribution of iron and copper after the reaction among pseudo-rust and the two solutions was obtained by chemical analysis, and the anion permeability through the rust was estimated by the sodium hydroxide consumption during the reaction. On the basis of these data, the protective effects of copper added to low-alloy steels were discussed.

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[in Japanese]

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