In order to obtain a satisfactorily decorative chromium plating from oxalic acid baths, effects of total chromium concentration, Cr⁶⁺ concentration, SO₄^2- ion, NH₄⁺ ion, pH, temperature and current density on the states of chromium electrodeposition were studied. The followings were determined as optimum. Bath composition; total Cr 100g/l, Cr⁶⁺ 12-38g/l, (NH₄)₂SO₄ 75g/l, and operating conditions; pH 1.8-2.5, current density of 10-300A/dm² at bath temperature 25-50°C or 20-300A/dm² at 60-80°C, carbon anode.

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TiO₂-Ni composite electrodes prepared by dispersion plating method were investigated in comparison with TiO₂ single crystal electrode in propylene carbonate solution. The electrolyte solution was 0.1M tetraethylammonium perchlorate (TEAP) solution. The working electrode was irradiated by a 500W xenon discharging lamp. The differences of mixed potentials, potentiodynamic curves and chronopotentiograms were measured under illumination and in the dark. Measurement of capacitance of the electrode-solution interface was performed by the bridge in combination with DC voltage scanner. Water content was analysed by an automatic Karl-Fischer analyser. Higher photopotential on the composite electrode was attained than on the single crystal electrode. Action spectra of photocurrent on this electrode were entirely similar with that on the single crystal electrode, and each value of photocurrnt on the former was by a few times larger than that on the latter. Mott-Schottky plot (1/C² vs. E) on the composite electrode showed nonlinear curve, which was probably due to the faradaic process of matrix Ni's anodic oxidation. Addition of TEAI or water as electroactive components resulted in the increase of photocurrent and showed saturation over 8mM and 10mM, respectively. Dissolution of matrix Ni occurred over +0.4V (vs. Hg/Hg₂Cl₂, Cl^-(pc)) and the dissolution was facilitated by the addition of I^-. But the electrode restored to its original state even after it had been polarized up to +2.8V for a few minutes.

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Electrodeposited diamond grinding wheel is made in Watt's bath in which the wheel body is rotated very slowly for the purpose of obtaining uniform deposited layer. Choiced factors in electrodeposition are deposit time, bath temperature and current density. Deposited layer adjacent to diamond grit grows faster than the other part of the wheel surface. So, it is conjectured that the diamond grits used in this experiment have some electroconductivity. Observation of grit position relative to the wheel body shows that pre-electrodeposited layer has enough strength for supporting grinding force. By the grinding experiments, electrodeposit conditions which give good grinding performance are found.

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In Hokkaido University, laboratory wastewaters are collected periodically, and treated in a treatment plant. Usually, the collected wastewaters are very acidic and contain various heavy metal ions as well as chelating agents. The precipitation of heavy metal ions as hydroxides will be incomplete unless the chelating agents are pretreated by oxidation. A special treatment process in which CrO₃, Fe³⁺, and Ca²⁺ are added prior to the neutralization with NaOH solution has been adopted to over- come this difficulty. This paper describes the basic research conducted to develop the treatment process, especially in relation to the oxidation of chelating agents by CrO₃. Among many chelating agents, EDTA, DTPA, and Tetren strongly interfere with the formation of metal hydroxides. However, EDTA and DTPA are easily decomposed by CrO₃. The effectiveness of CrO₃ addition is demonstrated for (A) an actual wastewater to which some EDTA had been added, and (B) a number of model wastewaters containing Fe³⁺, Zn²⁺, Cr³⁺ ions, EDTA, and other chelating agents. The proper operating conditions for oxidation, i.e. CrO₃ concentration, solution acidity, temperature, and reacting time are determined experimentally.

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Ionic mass transfer at a disk electrode placed at/or near the stagnation point of an impinging jet has been studied. An electrolyte was discharged into an open space from a circular nozzle and collided vertically with a flat plate, then flowed away forming an axially symmetrical stretching film. The limiting current density, i_L, for the electrodeposition of copper from 0.1mol/l copper (II) sulfate solution came up to 0.4A/dm² at the flow rate of 300cm/s (av. in the nozzle) and at 30°C. Higher value of i_L was obtained for an electrode located apart from the stagnation point. The impinging jet method was shown to be very effective for the acceleration of diffusion process at an electrode. The theory of convective diffusion at the solid-of-revolution electrode with stagnation-point flow was applied to present the rate equation for the mass transfer at the impinging jet electrode.

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