In recent years, the development of non-cyanide baths for electroplating of various metals has been demanded for the purpose of preventing water pollution in our country. However, since no suitable striking baths for copper have been found, cyanide baths have still been employed till now. For the settlement of this problem, many kinds of inorganic and organic copper complexes were examined for the use in the striking bath with respect to the adhesion of deposit film, the price and toxicity of the compound, easy treatment of the waste liquor, etc. As a result, sodium sulfitocuprate was selected among them. Its molecular formula was determined at first, and then, various conditions of electroplating were investigated on a bath containing that compound as the principal component. This striking bath was slightly deficient in stability; but a good copper deposit was formed on the steel surface under considerably low current densities.

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The effects of bath temperature on anodized aluminum film formed in alkaline bath was investigated. The baths used for the experiments at various temperatures (5-50°C) were as follows: (1) NaOH (0.1mol), (2) Na₃PO₄ (0.2mol), (3) Na₂CO₃ (0.1mol), (4) sodium tartrate (Na₂C₄H₄O₆) (0.1mol) added to each of the above baths, and (5) NH₄OH-NH₄F which had previously been reported. The thickness and properties of the films formed were compared with those of the anodized films formed in H₂SO₄, and the following results were obtained. (A) Effects of temperature on thickness of the film formed: A thicker film was obtained at a lower temperature. It was generally difficult to obtain a thick film by anodizing in a hot bath, because aluminum and its oxide film were easily dissolved in alkaline solution of high temperature. However, a thick film was formed in the above bath. (5) when the current density was higher. (B) Effects of temperature on hardness: A harder film was obtained at a lower temperature. (C) Effects of temperature on corrosion resistance: A film formed at a lower temperature showed a higher corrosion resistance. (D) Effects of temperature on wear resistance: Wear resistance became higher with the lowering of temperature. A film (about 9μ in thickness), which had been formed in NH₄OH-NH₄F bath and sealed with boiling water, had a wear resistance of higher than 1, 000 seconds.

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It was found that the zinc layer electrodeposited from zinc sulfate bath containing a small amount of Cr^VI very high corrosion resistance. Being motivated by this finding, we studied the effects of Cr^VI in zinc sulfate bath on the zinc plating and on the properties of zinc layer by chemical analysis, X-ray diffraction analysis, electron probe microanalysis, infrared absorption spectroscopic analysis, and electron microscopic observation. The results obtained were as follows. (a) The abovementioned zinc layer contained amorphous hydrated chromic oxide finely dispersed in the layer. (b) The hydrated chromic oxide content of zinc layer increased with increase in the amount of Cr^VI in the bath and increase in pH value of plating bath; but it decreased with the rise in bath temperature and increase in current density. (c) The corrosion resistance of zinc layer was higher when the hydrated chromic oxide content of zinc layer was higher; but the appearance and adhesion of the layer became poorer when the oxide content was higher than a considerable value.

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In the preceding paper, it was made clear that the zinc layer electrodeposited from zinc sulfate bath containing Cr^VI had high corrosion resistance, and it contained amorphous hydrated chromic oxide finely dispersed in the layer. This paper describes the mechanism of co-deposition of hydrated chromic oxide and zinc in the layer electrodeposited from zinc sulfate bath containing Cr^VI. The results revealed that the co-deposition of hydrated chromic oxide and zinc proceeded as follows. (a) Cr^VI in the plating bath was cathodically reduced to Cr^III; and concurrently, the hydrogen ion near the cathode was consumed by the following reaction, which made the film of chromic hydroxide precipitate on the cathode surface by means of the increase in pH value.
Cr₂O₇^2-+8H⁺+6e→2Cr(OH)₃+H₂O
(b) Chromic hydroxide on the cathode was converted into the coordinated polychromic hydroxide film, or hydrated chromic oxide film, by bridging of OH. (c) The reduction of Cr^III to Cr^II caused the breaking of hydrated chromic oxide film formed on the cathode, which led to co-deposition of zinc thereon.

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Chemical conversion treatments and painting were conducted for the zinc layer electrodeposited from zinc sulfate bath containing Cr^VI for the purpose of studing the effects of chemical conversion treatments on corrosion resistance and paint adhesion of the platings. The results obtained were as follows: (a) It was proved that when zinc plating in zinc sulfate bath containing Cr^VI was directly conducted on steel plate, hydrogen was occluded in the steel owing to hydrogen evolution in the early stage of electrolysis. As the result, when the plating was painted and baking-finished in the oven, the coated film was blistered owing to the release of hydrogen occluded in the steel. (b) Therefore, it was necessary to conduct plating in an ordinary zinc sulfate bath (in which no hydrogen evolution took place) before the plating in the bath containing Cr^VI for the prevention of blistering by hydrogen evolution. (c) Regardless of chemical conversion treatments, the zinc layer electroplated from zinc sulfate bath containing Cr^VI showed higher corrosion resistance and greater adhesive strength of coated film as compared with the layer electroplated from ordinary zinc sulfate bath.

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This paper describes the effects of alcohols on anodizing of aluminum in alkaline solutions for the purpose of improving transparency of the anodized film. To a solution mainly composed of 0.1mol sodium hydroxide or 0.2mol sodium phosphate were added 0.1mol polyhydric alcohols (ethylene glycol, glycerine, and sorbitol), and anodizing was performed in the solution. Investigations were made of the effects of additional alcohols on thickness and properties (scratch hardness, corrosion resistance, acid resistance, and alkali resistance) of the oxide film formed by anodizing. The results obtained were as follows: It was found that the addition of alcohols improved these properties in the increasing order of the number of their alcoholic hydroxide groups. Sorbitol had the most remarkable effects on these properties among them. It was suggested that the addition of alcohols prevented the dissolution of formed oxide film and increased the film thickness by co-deposition of electrolytic oxidation products of alcohols.

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It was observed that the structure of built-up films of stearic acid or stearyl alcohol formed on aluminum by employing Langmuir-Blodgett's technique is markedly influenced by surface conditions. The relationship between the number of built-up layers (N) and the number of times for lifting the specimens up through the monolayer film spread on the water (n) was examined by tracer technique, and it was found that the films were classified into the following two types according to the surface conditions: N=2n-1 and N=n. Built-up films of (2n-1) type that can be deposited, for example, on the substrates anodized in ammonium borate or electropolished in HClO₄ and glacial acetic acid had hydrophobic surfaces. On the contrary, the surfaces of n type films formed on the substrates such as boehmite or thick anodized films were hydrophilic. Determining whether the surfaces are hydrophobic or hydrophilic was made by measuring the contact angle or coefficient of friction. However, other built-up film surfaces deposited, for example, on an anodized substrate of less than 2μ in thickness, showed some intermediate properties, and this was interpreted in terms of irregular orientation of the polar organic compounds in the films.

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