Electrodeposition of palladium from the baths of dinitrodiammine, dibromodiammine and dichlodiammine has been carried out by applying pulsed current electrolysis. Surface morphology, grain size, internal stress and texture of the palladium deposits, electrode potential during the electrodeposition and the hydrogen content of the deposits were examined as a function of pulse parameters. A close correlation was found between crystallographic features of the palladium deposits and the mode of pulse current. A decrease in the grain size of the deposits was observed in pulsed current electrolysis using higher pulse current density, longer pulse on-time, and shorter off-time, which lead to the highr cathodic overpotentials. Although the desorption of hydrogen from the palladium deposits was expected to occur during off-time, this did not always occur. The effect of pulse current electrolysis was most remarkable in dinitrodiammine bath, which yielded a palladium deposit containing less adsorbed hydrogen than that obtained by DC electrolysis.

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The effect of pretreatment on the corrosion resistance of zinc-rich painted steel sheets was evaluated by salt spray tests and the corrosion behavior was investigated electrochemically and by ESCA. The results obtained were as follows, (1) Steel sheet with 6-7μm composite coating containing about 70wt% zinc powder showed excellent formability. (2) Cold-rolled steel sheet with composite coating had poor corrosion resistance, indicating the importance of the pretreatment. (3) Pretreatment by Zn-Co-Mo electrodeposition produced superior corrosion resistance to that produced by Zn plating. (4) The excellent corrosion resistance of composite coated sheet pretreated by Zn-Co- Mo electrodepositi on depended on two factors, a) the corrosion products of Co and/or Mo controlled the increase in the anodic and cathodic reaction rates, which decreased the dissolution of Zn in the plated layer and prevented the growth of blisters; and b) most of the Zn in the composite coating and in the plated layer remained as a corrosion product on the surface, protecting the steel sheet substrate.

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A study has been carried out to clarify the crystal growth mechanism of the tinplate during flow-brightening and quenching in electrolytic tinning. It was found that the “quench stain” -a ripple-like surface pattern, formed during quenching corresponds to the crystallization of the tin layer. The origin of the ripple pattern indicated the nucleation site and the crystal growth rate. At most of origins of the ripple pattern, the Fe-Sn intermetallic compound did not form on the substrate strip, indicating that the number of sites, where nucleation occurs depends on the surface cleanness of the substrate strip. It is suggested that surface contaminants introduce localized supercooling of the tin layer thereby controlling the grain size of the tinplate crystals, but because the degree of supercooling depends on cooling rate, grain size is also affected by the cooling rate of the steel strip. Actually, tin grain size increased when the amount of surface contaminants was reduced during pretreatment or annealing.

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The anodic oxidation of hypophosphite on nickel, palladium, platinum, gold and cobalt electrodes in sodium citrate solution was studied with special attention to the catalytic activity of the metals in electroless plating. The polarization curves exhibited the current peaks, that were probably attributable to the formation of anodic films on the electrode surface at noble potentials. The anodic currents of the ascending portion of the polarization curves increased with increases either the pH value or the concentration of hypophosphite. The reaction orders in regard to the concentrations of hyphosphite and hydroxyl ion were approximately 0.5 and 0.2 respectively, and were dependent to some extent on the type of metal electrode. The relative catalytic activity of the metals, evaluated by the potential values at an anodic current density of 1.0×10^-4A/cm², decreases in the order Au, Ni, Pd, Co and Pt. Anodic oxidation of hypophosphite did not occur on Cu and Ag electrodes. The apparent activation energies for the anodic reaction were 7.9, 11, 13, 21 and 14kcal/mol for Au, Ni, Pd, Co and Pt respectively. Thus, the activation energy of the metals in the anodic oxidation of hypophosphite increases in descending order of their catalytic activity.

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Film resistivity and structure of electroless Ni-W-P films were studied under changes in the concentrations of Na₃-citrate and Na₂WO₄. At higher concentrations of Na₃-citrate, the codeposition of tungsten reduced the phosphorus content of the deposits but film structure remained amorphous. Film resistivity was independent of thickness even at the initial stage of deposition. Thermal analysis gave two distinct exothermic peaks, which were shifted to the higher temperature by an increase in co-deposited tungsten. It was confirmed that the film resistivity and crystal structure of Ni-W-P films did not change drastically with heat variation, and that the stability against thermal treatment of the Ni-W-P films was much greater than that of commonly used Ni-P films.

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