Four kinds of sintered ZrB₂ solids-thermal impulse resistive TR, antifrictional HZ, oxidation resistive OR, and corrosion resistive CR, were studied in aqueous and propylene carbonate solutions at room temperature for the purpose of applying them to solid electrodes for electrolysis of some kinds of redox systems and of electroanalysis. As in the case of glassy carbon electrodes very small residual currents were observed on the anode branches of cyclic voltammograms for TR and HZ. And the redox systems [Fe(CN)₆]^3-/[Fe(CN)₆]^4-, I₂/I^-, and quinone/hydroquinone showed electrochemically reversible redox current waves at the electrodes. On the other hand at electrodes OR and CR, large residual current waves over 1.2mA/cm² height were observed in the potential range 0-0.6V vs. Ag/AgCl, Cl^-, which may have been caused by oxidation of sintering reagent SiC of the solid. All of the electrodes used here were very inert in alkaline solutions of pH of 12 or higher, due to being covered with the reaction product Na₂SiO₃ layer. In propylene carbonate solution, TR and HZ behaved as in aqueous solution, but OR and CR seemed to have a high resistant film on the surface which allowed charging and discharging current across itself.
It is suggested that studies of the electrocatalytic characteristics of these materials and of characteristics as an electrode for electrolysis at high temperatures at which the inherent properties of ZrB₂ are fully utilized must be carried out for more redox systems than were studied here.

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High purity aluminum foil was electrochemically etched with 50Hz rectangular alternating current and the effects of pretreatment on the morphology of the etched surface was discussed. The pit density and size observed by SEM was influenced greatly by the pretreatment conditions. Specifically when the samples were heated to 200°C or above in air after boiling in distilled water for 10min, no pits development occured. Sufficiently protective film was formed and virtually Square-wave chronopotentiometry allows the determination of an induction time which depended on current density and the pretreatment adopted. The resulting electrostatic capacitance of etched and anodized foil was increased by the addition of some amount of sulfuric acid to 10% hydrochloric acid solution except in the case of heating after boiling.

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The electrodeposition behavior of Ni-Cd alloys was investigated using sulfate baths. It was found that over a wide range of electrolysis conditions the codeposition behavior of Ni-Cd alloys was anomalous because the Ni content of the alloys was extremely low in comparison with the metal-percentage of Ni in the baths. The Ni content of the alloys increased with increases in the Ni concentration in the baths, current density, pH and temperature, and with a decrease in the sodium acetate concentration in the baths.
The polarization curves were measured during the deposition of Ni-Cd alloy and each component metal. In the alloy plating bath, Ni deposition showed significant polarization which brought about the anomalous codeposition while Cd deposition began to occur at around the equilibrium potential of Cd. The high polarization of Ni deposition was observed even in a Ni single bath. Therefore, the anomalous codeposition appearing in the Ni-Cd system is not attributed to the interaction of both ions during their simultaneous discharge, but to the polarization peculiar to single Ni deposition from aqueous solutions.

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The effects of heat treatment on the wear resistance of electroless nickel deposits were investigated using a Nishihara wear tester, Suga abrasion tester, pin-disk wear tester and a Falex wear tester.
The results obtained are summarized as follows:
(1) Measured using a Nishihara wear tester, the best wear resistance was attained by heat treatment for 1hr at 600°C. Heat treatment for 1hr at 400°C decreased the wear resistance of deposits.
(2) Measured using a Suga abrasion tester, the wear resistance increased linearly with increasing hardness of the heat-treated deposits.
(3) Measured using a pin-disk wear tester and a Falex wear tester, the wear resistance improved remarkably after heat treatment for 1hr above 300°C.
Therefore, it is concluded that electroless nickel deposits can be very useful wear resistant material provided it has been heat-treated for 1hr at 500-600°C.

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