Copper and nickel ions in waste solutions can be recovered as metal-formamide complexes with over 90% recovery efficiency. It is possible to use these recovered metal-formamide complexes as electrolyte again for metal plating. The nickel deposit obtained from the regenerated bath has a hardness value of about 500Hv, a strong [200] grain orientation, and a grain size of 88-129Å.

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Electrodeposited chromium of 30μm in thickness was diffused into its 0.2% C substrate steel by high-frequency induction heating; the frequency varied from 8kHz to 9MHz. Interdiffusion coefficient between chromium and iron was greater in high-frequency induction heating than in conventional electric heating, and showed a maximum value within the above range. It is concluded that the skin effect produced by the high-frequency induction heating causes an increase in the rate of chromium diffusion into carbon steel.

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Thermal expansion of the anodic oxide layers of aluminum formed in certain aqueous electrolytes, such as sulfuric acid, oxalic acid, sulfuric-oxalic acid mixture, and sulfosalicylic acid has been investigated for each type of the films on the assumption that this phenomenon is different between inorganic acid and organic acid films. An attempt has been made to explain these phenomena in terms of the film growth in four different electrolytes. In a case of using inorganic acid, thermal shrinkage of films occurs up to 200°C, but in another case of using organic acid, it occurs up to 900°C. And the phenomenon has shown a reversible change within the temperature range from 25°C to 700°C. The possible causes for the thermal shrinkage investigated here may be due to the difference of thermal expansion coefficient between film surface area and film-aluminum interface area or at least in the film structures.

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Ta sheets were calorized in a quartz ampoule by using Al vapor generated from the powdered FeAl₂ alloy at 1000°C for various durations of pretreatment. The Ta-Al alloy layer formed on the surface was examined by microscopy, X-ray diffraction, and electron probe micro-analysis. It was found that the calorizing process of Ta sheets obeyed a parabolic rate law and the rate constant was about one third of that for siliconizing (formation of TaSi₂ layer) under the same conditions. The alloy layer formed was mainly of TaAl₃ compound and the formation of its layer proceeded through only an inward diffusion of Al, but the transient initial process was found to occur relatively rapidly to form a low Al-Ta alloy layer through the mutual diffusion of both Ta and Al atoms, which was recognized by the existence of Ta oxide particles as the markers. After a long duration of valorizing process (25hr), the surface of the alloy layer was found to be converted gradually into a low Al-Ta alloy owing to the slight decrease of Al vapor from the powdered Al-source, though the overall kinetics of the process showed no alteration.

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Loss of fluorides added to the Cr plating bath as catalyst for electrodeposition was observed in the recovery process of the bath by vacuum evaporation. This was attributed to the evaporation loss of HF formed as a result of dissociation of the added fluorides. Evaporation of HF took place together with evaporation of water and was affected by the pressure and concentration ratio of the vacuum evaporator. The loss of fluorides increased with increasing evaporation temperature and chromic acid concentration.

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Plating conditions obtained by using Hull Cell cover a wide range of electric current density, so that this cell has been used generally for decision of plating conditions or selection of plating baths. In order to utilize the results of plating in Hull Cell, a few experimental equations of the distribution of current density on the cathode have been proposed. These equations are shown as straight lines on semilogarithmic graph paper concerning the points on cathode and the current densities. In this study, we selected a cupric sulphate solution as plating bath for Hull Cell test and measured the film thickness by two methods: microscope and electromagnetic meter; the current density was calculated from the film thickness. Theoretical current density was obtained by means of conformal mapping. The current density measured by the microscopic method agreed with the theoretical current density. In regard to the relation between logarithm of distance from the bottom of cathode and current density, we propose an approximate equation, combining two straight line formulas, instead of the traditional equation which is a straight line formula, because the former is much more accurate than the latter.

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With an object of decreasing the bath voltage during hard anodizing of Al (99.99%) in a tartaric acid bath (1mol/l), effects of several additives (0.01 to 0.5mol/l) on the bath voltage, local corrosion of anodes and hardness of films were examined at 40°C and 1.87A/dm². Grayish brown and hard (Hv585) films were formed with tartaric acid at 190V. By adding 0.5mol/l sulfuric acid, non-colored and uniform film was obtained at 19V but it was not so hard (Hv250). With sodium sulfate and sulfamic acid, the bath voltage decreased but local corrosion took place under every condition. The film formed by adding 0.5mol/l phosphoric acid at 115V was uniform but soft (Hv65). When oxalic acid was added (0.01 to 0.5mol/l), uniform films were formed at 60 to 130V; the hard films more than Hv400 were obtained by adding 0.1mol/l oxalic acid at 70 to 90V. Through these experiments, oxalic acid was found to be the most suitable as additive.

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