Laboratory studies have been made on chromium plating from the low concentration bath containing CrO₃ 50g/l, H₂SO₄ 0.5g/l, and Na₂SiF₆ 0.5g/l. Compared with the deposits from the conventional high concentration bath, the chromium deposits from the low concentration bath were almost similar in respect of bright area, throwing power, covering power, current efficiency, hardness, crack and corrosion resistance etc. Also, the industrialization of chromium plating from the low concentration bath has been made successfully in a full automatic batchtyped and a handtyped plating process in a plating factory. In the fomer process, Sargent bath constituents could be reduced to CrO₃ 100g/l, H₂SO₄ 1g/l by stopping replenishment of CrO₃ and H₂SO₄. In the latter case, the bath was diluted with water to the above mentioned low concentration. Consequently, the amounts of CrO₃ supplied, rinse water, chemicals for effluent treatments, and sludge produced were remarkably decreased with lowering concentration of CrO₃ in the chromium plating bath.

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This paper deals with the composition and electrochemical properties of the γ_l and γ_s-layers constituting the boehmite films on Al. The boehmite films were produced by soaking Al specimens, previously treated with a H₂SO₄-HNO₃ solution, in boiling distilled water for 20 minutes. The γs-layer next to the metal was exposed by dissolving the outer γ_l-layer in a boiling phosphoric acid-chromic acid solution (20g of CrO₃ and 35ml of 85% H₃PO₄ in 1l of distilled water) for 10 minutes; the γ_s-layer was found to be almost non-soluble. It was also found in a 0.5M NaCl solution that the corrosion potential of the specimen covered with the original (γ_l+γ_s) boehmite film is -1.1V (vs. S.C.E.), and the value is about 0.3V more negative than that measured after the γ_s-layer has been exposed. This is consistent with the fact that the presence of the γ_l-layer causes an increase in cathodic polarization and inhibits the corrosion of the substrate metal. Examinations of the composition of the layers by X-ray diffraction and electron diffraction show that the γ_i-layer and γ_s-layer consist mainly of γ-AlOOH and a-Al₂O₃, respectively.

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The purpose of this paper is to investigate the esterification of the surface hydroxyl groups of hydrated alumina powder (main constituent being boehmite) with normal chain alcohols, for hydrophobing of anodic oxide film on aluminum. Esterification was carried out by the reflux method. The surface hydroxyl groups of the hydrated alumina powder was esterifled with alcohols as -OH→-OR (R: alkyl group), and the amount of alkoxy group calculated from the data of ultimate analysis was about 4-5×10^-4mol/g. The esterified powders showed hydrophobic properties. They floated on water, and this effect was remarkable in the case of treatment with a mixed solution of 1-dodecanol and dodecane, where the treated powder never sedimented in water. The surface hydrophilicity of the powder wasdecreased to about 1/3 of that of the original powder.

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A study has been made of the effect of tin and phosphorus content of the bath on the properties of electroless nickel-tin-phosphorus alloy deposits obtained from ammonia alkaline bath. The alloy deposits containing up to 1.0% tin and 3.4-5.4% phosphorus can be obtained by an addition of sodium stannate to the plating bath. The deposition rate of the alloy containing 0.25% tin was the lowest, because tin reacted as an inhibitor on the nickel surface. It was also found that the corrosion resistance of the nickel-tin-phosphorus deposit containing 0.46% tin and 3.97% phosphorus was most enhanced in 1N sulfuric acid by the presence of tin and phosphorus.

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The structure of anodized film on aluminum formed in alkaline bath containing hydrogen peroxide at constant voltages has been studied by electron microscopy. Electron micrographs of the section of anodized film showed that the pores were branched. This structure is much different from the vertical and regular structure proposed by Keller and others. It was found that the pores on the surface increased in size and joint to each other in proportion to anodizing time and that the columns in the wall were widened with a rise in electrolytic voltage. Thickness of the barrier layer was about 12Å/V and not greater than that of the barrier layers formed in ordinary sulfuric acid baths.

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Dyeing affinity, cell size, and cross-section of the anodized films produced in alkaline solutions (0.1M-NaOH, 0.1M-Na₂CO₃, 0.1M-Na₃PO₄, and NH₄OH-NH₄F system bath) were compared with those of the films produced in H₂SO₄ solution. The surface and cross-section of the thin anodized films which were obtained by complete anodizing of aluminum foils and also the surface of the substrates from which the oxide films had been removed were observed by SEM. The pore walls in the anodized films formed in NaOH and Na₃PO₄ were uneven compared with those in the films formed in NH₄OH-NH₄F or H₂SO₄. Observation of the surface and cross-section of the films prepared in Na₃PO₄ revealed deposits which seemed to be phosphates or hydroxides. It was found that the bottom size of the cell was linearly proportional to the electrolytic voltage regardless of the bath composition. On the other hand, the differences in permeability, dyeing affinity, and adsorption amount of the dyestuffs (acid, basic, direct and mordant) were determined by mesuring the reflection absorbance of the dyed films and by a colorimetric method. Dyestuffs were adsorbed to a greater extent in the film prepared in Na₃PO₄ than in any other films produced in alkaline solutions. The amount of the adsorbed dyestuff decreased in the order of the following kinds of films: Na₃PO₄>NaOH>Na₂CO₃>NH₄OH-NH₄F>H₂SO₄ films. The amount of dyestuff passed through the thin anodized film produced in NH₄OH-NH₄F was about two times as much as that produced in H₂SO₄. SEM observation and dyeing tests suggest that the anodized films formed in alkaline solutions have larger pores and cells as compared with the films anodized in H₂SO₄.

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