The corrosion resistance of tin-nickel alloys deposited from pyrophosphate bath has been estimated by the CASS and salt spray tests as well as by the measurement of the electrode potential and polarization curves of the alloys. The deposited tin-nickel alloys seemed to be attacked more easily by hydrochloric acid than by sulfuric acid or nitric acid. The weight loss of the deposit in nitric acid solutions was smaller than that in the other acid solutions. The tin-nickel deposits had high corrosion protection for the underlying metal in the CASS and salt spray tests, therefore, the deposits can be used as to a decorative and corrosion resistant coating. Pre-electrolysis of the deposits tarnished them slightly during the CASS test, due to the deposition of copper contained in the CASS test solution. Immersion of the deposits in 10% nitric acid or 3% Na₂Cr₂O₇ solution prevented the deposits from tarnishing for 48 hours in the CASS test.

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It is well accepted that the electroless plating of metal is understood by the superposition of the anodic oxidation of reducing agent and the cathodic deposition of metal according to the mixed potential theory. Following to this concept, the rate of electroless plating of cobalt was estimated by the partial polarization curve method as well as the polarization resistance method. The standard composition of the electroless plating bath consisted of 0.1M CoSO₄, 0.2M NaH₂PO₂, 0.2M Na₃C₆H₅O₇ and 0.5M H₃BO₃. The partial polarization curves were simulated by the polarization curves in the bath eliminating either NaH₂PO₂ or CoSO₄ from the standard bath composition. The rate of electroless plating estimated from the partial polarization curves was remarkably less than that obtained by the weight gain measurement. The discrepancy was attributed to the fact that both the anodic and the cathodic polarization curves were strongly affected by pH and not independent each other. On the other hand, it was found that the rate was inversely proportional to the polarization resistance in good agreement with the theory of polarization resistance. Therefore, it is expected that the polarization resistance method is satisfactorily used in monitoring the rate of the electroless plating.

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Anodic oxidation of high purity aluminum in sulfuric acid bath produces colorless oxide layers by DC, but yellow oxide layers by AC. Using a rectangular AC (V_a=+20V, V_c=-10V, 50-10, 000Hz), a light brown colored oxide layer was formed accompanied by a faint electroluminescence. The color depends on the AC frequency used. The integrally colored oxide layer showed also a faint photoluminescence by UV irradiation. From these results the authors propose the following scheme of the coloration: At the moment of the polarity inversion, the trapped electrons inside the barrier layer are excited to the conduction band of the oxide and are accelerated by high electric field induced by the dielectric polarized space charge. These high energy electrons (2-5eV) then collide with the incorporated sulfate ions, which are eventually converted into the elementary sulfur.

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Electrolytic treatments have been widely conducted for concentrated cyanide waste solutions, but for diluted waste solutions only to a minor extent. This study has been made of an electrolytic treatment of residual copper cyanide in the second rinse water from a cyanide bath in a continuous circulation system. The plating solution contained 39g/l Cu (as metal), 82g/l NaCN (free), 30g/l NaOH and a small quantity of a brightener. The electrolysis was carried out using a graphite anode and a copper cathode under the conditions of D_A of 0.15A/dm² and D_K of 0.15A/dm², a bath temperature of 40°C and a circulating influx rate of the second rinse water of 180l/h. When the rate of dragout from the plating solution was about 1.2l/h, average concentrations of copper and cyanide in the second rinse water during continuous circulation (electrolysis) were about 130mg/l and 280mg/l respectively, which were about 1/40 and 1/25 of those in the first rinse water. This showed that dischaged substances were reduced to less than about 1%. The electric power consumption was about 60kWh/month. This type of rinse water did not have an adverse effect on the plated products over a long period in continuous use. Insufficent agitation of the second rinse water, however, produced stain on the products, presumably due to the high concentration of alkaline substances. Therefore, the removal of alkaline substances from the second rinse water by electrodialysis and improvement in durability of the anode could make this method practical.

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