Anodic oxide films formed on aluminum in sulfuric acid, have been electrolytically colored in a mixed aqueous solution of nickel sulfate and boric acid with sinusoidal alternating current. Deformed form of the current wave observed on a synchroscope, consisted of three components: non-Faradic current (i_NF), anodic current (i_a) and cathodic current (i_c). These currents were measured separately. It was found that i_NF was due to the current pass through the capacitive component of the barrier layer, whereas i_a was due to the re-anodizing of the oxide film in the coloring bath, and observed only in the beginning of a. c. electrolytic coloring. Decrease of i_c during a. c. electrolytic coloring seemed to be mainly due to the deposition of aluminum hydroxide in the pores of oxide films.

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An explanation of the origin of integral color anodizing of aluminum has been proposed in terms of the ratio of the cell size to the pore diameter of the oxide layer, which is characteristic of bath voltage and the electrolyte used. The P ratio, the ratio of cell radius to pore radius, was found to play an essential role on the current density at the pore bottom. For semi-spherical current flow at the pore bottom, the theoretical ratio of the current density at the pore bottom to the density at the metaloxide interface was proportional to the P². Electronmicroscopic observations of the cross section and/or transmission photographs of the porous oxide layer indicated that the integral color anodizing is probably obtained under such a condition that the P ratio is more than 5. In such a case, concentration of electrolytic current at the pore bottom induces an extremely high field strength (1×10⁹V.m^-1), by which electrons are injected into the oxide layer and further accelerated to gain an energy enough for breaking or for exciting bonds of organic compounds in the oxide film. Since the incorporation or inclusion of organic anions in the oxide film is always detected irrespective of the coloration, the incorporation of the organic anions itself is not the origin of the color, but the break or excitation of bonds of organic anions by high energy electrons should, at least, take part in the formation of the colored oxide film.

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For the purpose of recovering sodium hyroxide and zinc from waste water from low cyanide zinc plating baths, an electrolytic technique was investigated using cation exchange membrane as diaphragm. Granulated graphite anode used exhibited exellent durability and high efficiency for decomposing cyanide. Continuous operation tests showed that the recovering rates of sodium and zinc ions were 10.2mg/min and 1.4mg/min at diaphragm c. d. of 2A/dm² (the area of the diaphragm on one side was 0.44dm²). Zinc was found to accumulate in the graphite anode as zinc hydroxide and zincate. The amount of zinc recovered was almost 90%.

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Although carbide coated steels prepared by immersion in a fused borax bath have a high corrosion resistance, local corrosion often appears on them. As one of preventive means against local corrosion, steels were plated before carbide coating in the present study. Investigations were made of the surface layers formed on chromium-, nickel-, and copper- plated steels immersed in a fused borax bath containing powders of Fe-V, V₂O₅+B₄C, Fe-Nb or Cr, and of the corrosion resistance of the treated steels. A layer of VC, NbC or (Cr, Fe)₇C₃+(Cr, Fe)₂₃C₆ was found to form on chromium- and nickel- plated steels, by a reaction between V, Nb or Cr, dissolved in the borax and carbon atoms supplied through the plated layer from the steel matrix. In this immersion process, chromium- and nickel- plated layers transformed into a carbide layer of (Cr, Fe)₇C₃ and a solid solution layer of Fe-Ni-C, respectively. Double carbide layers of VC or NbC+(Cr, Fe)₇C₃ were observed on a chromium- plated steel. In Cr- plated steel immersed in a borax bath containing Cr powders, a (Cr, Fe)₇C₃+(Cr, Fe)₂₃C₆ layer was formed on a (Cr, Fe)₇C₃ layer, but these carbide layers were observed as a single layer under a microscope. In copper-plated steel, any carbide layer was not formed. Chromium- plating gave a protective effect on the generation of local corrosion of carbide coated steels in 36% HCl aqueous solution, but nickel- plating gave little effect.

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