Cathodic current-potential curves were measured for iron of 99.94% in purity in chromic acid solutions containing various amounts of sulfates. The curves were characterized by the presence of two current waves, III and IV, which appeared in the range of 0.40-0.95V and under -0.95V (vs. SCE), respectively. The wave II, observed for the platinum electrode in the potential region above -0.45V, was not observed for the iron electrode. The partial currents for electrode reactions and the amounts of Cr and Fe ions incorporated into the chromic-chromate films were measured as functions of the cathode potential. The effect of the composition of solution was also examined. It was found that a group of reactions [Cr(VI)→Cr(III)_aq., H⁺→H₂, and Cr(VI)→Cr(O)*] proceeded in the waves, II and IV. However, the formation of metallic chromium marked with an asterisk was not observed before the potential was lowered to under 0.8V. The chromium content or the thickness of chromium-chromate film was found to increase in a stepwise fashion with the lowering of potential. In any cathode potential, the thickness of the film decreased with the increase of sulfate concentration; and the concentration of chromic acid had little effects on the film thickness. The Fe ion content of the film was considerably high at above -0.45V, but dropped to a small value when the potential was lowered to under -0.7V. The characteristic features of current-potential curves and the mechanism of cathodic reduction of chromic acid on the iron electrode were discussed on the basis of these facts.

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Electrolysis of aluminum under A. C. in alkaline solutions containing metallic salts, organic acid salts, and fluorides were conducted. Concentrations of additives were as follows: alkali carbonate (sodium carbonate and ammonium carbonate): 0.3-0.8mol, metallic salts (silver, copper, ferric iron, nickel, and antimony): 0.02mol, organic acid salts (tartrate and citrate): 0.05-0.2mol, and fluorides (ammonium fluoride and sodium fluoride): 0.15-0.2mol. Colored films (about 4-5μ in thickness): were prepared by electrolysis under A. C. of 2-3amp/dm² at 20±1°C for 30min. In sodium carbonate solution, a yellowish green film was formed in a bath containing copper salts, a brown film in a bath containing iron salts, and blackish brown film in a bath containing nickel salts. On the other hand, in ammonium carbonate solution, a yellowish brown film was formed in a bath containing silver salts, a black film in a bath containing nickel salts, and a blackish brown film in a bath containing antimony salts. Experiments results of the properties of the above colored films showed that acid resistance (to 10% H₂SO₄) and alkali dropping test (10% NaOH) were equal or superior, but hardness (by Martens' scratch hardness tester) was inferior to those values of anodized films of nearly the same thickness prepared in H₂SO₄.

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In recent days, the surface contamination with flaky graphite has frequently occurred during subcritical annealing of low carbon mild steel sheets. For instance, the graphite leads to a tarnish of tin plates, which gives rise to serious troubles in many plants. The preceding experimental results revealed that the contamination was not due to the sooting from inert gas atmosphere or the carbonization of residual oil on the steel surface during annealing, but to the graphitization of carbon in the steel. This study was made on the graphite formation on low carbon mild steel surface during its annealing process. The investigation was performed by means of direct microscopic examination of polished specimens at elevated temperatures, At first, the graphite formation occurred on the surface of the overcropped carbide particles by decomposition of the carbide and the graphite flakes grew up over the ferrite surface. It was made clear that the crystal surface of steel substrate had preferential orientation for the growth of graphite flakes. X-ray and electron diffraction patterns showed that (00·1) of graphite formed on the steel surface was parallel with the surface of steel substrate. The graphite formation was observed at subcritical temperature (below A₁), not above A₁. The graphite flakes, which had been formed at subcritical temperature, were dissolved into the steel when heated at above A₁; but they appeared again in the same position as before when the temperature was lowered to below A₁. The distribution of carbide showed the diffusion of carbide particles on the surface during annealing. The diffusion was not due to the gradient of carbon concentrations, because there was a difference in carbide distribution between the product annealed in vacuum and that annealed in N₂ mixed gas atmosphere.

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Behavior of halogen ions to anodized aluminum films was investigated when the films were dipped in sodium halide solutions. The following results were obtained: (1) The decreasing order of adsorption of halogen ions on the anodized film in H₂SO₄ was arranged as F′>Cl′>Br′. The amount of adsorbed F′ increased with the increase in concentration and film thickness and rise of temperature; also increased on more acidic side. (2) The amount of adsorbed F′ on the anodized film in H₂SO₄ decreased by treatment with boiling water. (3) The decreasing order of adsorption amount of F′ on various anodized films was arranged as in H₂SO₄> in (COOH)₂> in Na₃PO₄> in NH₄F-NH₄OH solution. (4) The decreasing order of the amount of passed halogen ions through a thin anodized film (formed by thin aluminum foil) was arranged as Cl′>F′>Br′. The amount of passed F′ decreased on more acidic side. The film prepared in NH₄F-NH₄OH solution had greater passability than that in H₂SO₄. In the next stage, the sealing effects of metallic halides were investigated and the following results were obtained: (A) The best results were obtained by addition of chromium or nickel fluoride to the film prepared in H₂SO₄. (B) The sealing effects of metallic halides had a similar tendency to the adsorption of halogen ions. (C) The suitable conditions for sealing treatment were about 0.02mol of concentration of solution, about 50°C of temperature of treating solution, and about 10min. of dipping time.

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The present investigation relates to the electrophoretic deposition of a water soluble paint on aluminum film, which is simultaneously anodized in an alkaline (triethanolamine or ammonium hydroxide) solution. The following two kinds of solutions were used for electrolytic baths. (1) About 0.3% solution of an electrodeposition paint containing ammonium hydroxide (2mol), ammonium tartrate (0.1mol), ammonium fluoride (0.3mol), and ammonium carbonate (0.1mol). (2) About 2% solution of the same paint as in (1) containing triethanolamine (1mol), ammonium fluoride (0.1mol), and tetramethyl ammonium hydroxide (0.2mol). As the results of anodizing in above solution (1), a film obtained by two-step electrolysis (i. e., anodizing for 15min. under D. C. of 4Amp/dm² and then, anodizing again for 35min. under D. C. of 2Amp/dm²) was about 35μ in thickness, which was thicker than a film (about 27μ in thickness) formed in the solution containing no electrodeposition paint. On the other hand, in above solution (2), a film (11μ in thickness) was formed by electrolysis for 60min. under D. C. of 2Amp/dm². The results of thermal analysis, infrared spectroscopic analysis, and microscopic examination showed that the paint which had been dissolved in the bath was contained in the film obtained, which is called “a simultaneous electrodeposition film”. It was observed that the amount of paint contained in the film anodized in above solution (2) (measured value 36%) was greater than that anodized in above solution (1) (measured value 12%). Therefore, the film formed in above solution (2) had very higher alkali resistace (to 10% NaOH) and higher scratch hardness (by Martens' hardness tester with a load of 50g) than the film anodized in the same alkaline bath containing no paint.

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A continuous microscopic observation method for a certain definite point on the surface of electroetched chromium deposits was studied and the following results were obtained.
The width and number of cracks increased by etching, but cracks once produced never disappeared. When these cracks were observed with a scanning microscope, some cracks, which had come across a crack enlarged by etching, were more etched and developed in tunnel form.
Non-clear network patterns as well as clear cracks were observed with an optical microscope on the surface of bright chromium plating. These non-clear network patterns corresponded with the cracks produced by electroetching. Therefore, the non-clear patterns observed on the surface indicated all the cracks existing inside the chromium deposits.

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Following the preceding paper “Abrasion Resistance of Anodic Oxide Film Impregnated with Lubricating Oil”, this paper describes the experiments with MoS₂ as impregnating material by using Okoshi's Rapid Wear Testing Machine. The following results were obtained: (1) Abrasion resistance of porous films impregnated with MoS₂ was excellent and its value remained almost constant at high friction velocity. (2) The maximum abrasion resistance was observed when the films were heat-treated at 200°C; but, the value gradually decreased when the temperature of treatment was higher than 400°C. The resistance of the films heat-treated at 200°C was proved to be remarkably excellent by testing at a high frictron velocity. (3) The resistance was higher with the increase in MoS₂ content of the oil, but it became lower when the content was more than 20%.

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