The effects of composition and concentration of sulfate bath on the cathodic polarization curves and on the internal stress of Ni-Cd electrodeposit have been investigated. Limiting current density (l.c.d.) for Cd²⁺ deposition is influenced by Ni²⁺ discharge, if [Cd²⁺]/[Ni²⁺]>12×10^-2. In the bath concentration range where Ni²⁺ discharge has no influence on l.c.d. of Cd²⁺, the internal stress of electrodeposited alloys shows deflection of expansion, which is a typical property of Cd. In the concentration range where Ni²⁺ discharge has an influence on l.c.d. of Cd²⁺, on the other hand, the internal stress of electrodeposited alloys shows deflection of contraction, which seems to be interpreted in terms of an interaction between Cd²⁺ and Ni²⁺. However, in the case that [Cd²⁺]/[Ni²⁺]=12×10^-2 the electrodeposited alloys show no deflection.

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By using N, N-dimethylformamide(DMF), an aprotic polar solvent, the electrodeposition of lead from PbCl₂-DMF and Pb(NO₃)₂-DMF solutions was studied. The deposits of lead gave rise to the welldefined dendrites, when the electrolysis was carried out in higher concentration bath and at higher current densities, while at lower current densities (-3mA/cm²), the deposits became dark-gray and smooth. The dendrites of lead were of 2D [110], 3D [110] and 2D [100] types. The deposits from PbCl₂-DMF solutions were the isolated nuclei of the layer growth (hexagonal, tetragonal and trigonal deposits), when temperature was higher than 40°C. The deposits from Pb(NO₃)₂-DMF solutions were white powder when temperature was higher than 50°C, while at 100°C the dendrites were not observed. The X-ray analysis of the deposits of crystalline lead had well-defined diffraction patterns. By the addition of thiourea and 2-butyne-1, 4 diol to Pb(NO₃)₂-H₃BO₃-DMF baths, semi-bright and smooth lead deposits were obtained. They had fine grains in crystal structure and were found to have the strong preferred orientation of (220). The grain size of the deposit was 150-350Å. From these results the optimum condition for the electrolysis was as follows: Pb(NO₃)₂: 100g/l, H₃BO₃: 10g/l, (NH₂)₂CS: 4g/l, HOCH₂C≡CCH₂OH: 3g/l, temperature:room temperature, current density:0.5-1.0mA/cm², plating time: 60min, current efficiency: ca 50%.

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Failures in soldering sometimes occur even with the electric and electronic parts on which metals having good solderability are electroplated. In this paper, the effects of pretreatment processes prior to plating and thickness of electroplated coatings were examined to prevent these failures. In order to keep good solderability during 24 hour vapor treatment, bright tin-lead alloy coating on a copper panel was found to be effective than bright tin or dull tin-lead alloy coating, even if the lead content in the bright tin-lead alloy coating was only 5%. The bright alloy coating of 1μ in thickness was sufficient to keep good solderability on a copper panel. For other metals, however, copper undercoating of 0.5μ on kovar, 1μ on brass and phosphor bronze, and 3μ on steel were required to prevent deterioration of solderability when the thickness of bright alloy overcoating was only 1μ. In the case of nickel undercoating, severe deterioration of solderability occurred upon vapor treatment. When thickness of the overcoating was 3μ, undercoating was not required except a brass panel. Moreover, copper or nickel undercoatings of 0.5μ in thickness on brass and other base metals were also effective to keep good solderability.

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The structures and surface states of chromium coatings electrodeposited by applying rippled direct current of various frequencies have been investigated by microscopy and X-ray diffraction. The current applied was obtained by amplifying and rectifying signals of a RC-oscillator. The bath was of Sargent type (50°C) and the cathode current density was 30A/dm². The surface of chromium coatings varied from gray to bright via milky gray with increasing ripple frequency, and this was closely related to the current interruption time in unit Hertz. The gray chromium was of bcc and hcp mixed structures and the ratio of the hcp chromium increased in proportion to the current interruption time in unit Hertz. In previous works, it was found that the necessary factors for the deposition of the hcp type chromium were 1) high concentration of chromium acid in the bath, 2) low temperature of the bath, 3) high current density, and 4) use of pulsating and rippled current. But from the result of this paper, it was found that the application of rippled current with a long current interruption time (0.4msec. in minium) made it possible to deposit the hcp type chromium. The hardness of the coating decreased with increasing the ratio of the hcp type chromium.

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The formation of cathodic films on zinc plated steel sheet by electrolysis of aluminum biphosphate solution was studied. The corrosion resistance of zinc plated steel was promoted remarkably by the formation of this conversion coated thin film. The film provides good protection against rusting and improves the adhesion of paint as well. The formation of the conversion film was considerably affected by variation in the current density during electrolysis and pH. The effects of electrolytic conditions, such as current density and pH, on the formation of cathodic films were determined by measuring the potential-time curves and corrosion resistance to salt spray. It was found that the film was formed at a pH above 2.4 and at a current density above 2A/dm². The film formed on zinc plated steel sheet was found to possess a high formability.

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