The influences of chloride and sulfate ions in natural aqueous solution on the anodic dissolution of copper were investigated using electrochemical techniques. The anodic dissolution mechanisms of copper were proposed using determining the reaction parameters by the anodic polarization curves. The valencies of the copper ions were also determined using channel flow double electrode. The anodic dissolution mechanism changed depending on the concentrations of chloride and sulfate ions in fresh water : specifically, between (1) a concentration range with trace amounts of chloride and sulfate ions, and (2) a concentration range with more than about 100ppm of chloride and sulfate ions. The anodic polarization curve didn't show pH dependence in concentration range (2), but did show pH dependence in concentration range (1). The anodic dissolution mechanisms in concentration range (2) are proposed to be as follows. In the chloride medium : Cu+Cl−=CuCl+e− CuCl+Cl−→CuCl2− In the sulfate medium : Cu+SO42−=CuSO4−ads+e− Cu+CuSO4−ads+2SO42− →CuSO4−ads+Cu(SO4)22−+2e− Cu(SO4)22−=Cu2++2SO42− The influence of silica in fresh water on the anodic polarization curve was discussed.
In order to reproduce the initial process of the electroless plating of Ni on Al prepared with a double zincate pretreatment, a model electrode was prepared in which a small Zn tip was pressed to an Al plate. The immersion potential of the model electrode during plating was around-1 V for the first few seconds, which corresponds to the period of Zn dissolution, and then shifted to about-0.6 V which corresponds to electroless Ni plating on the Ni-P layer. By applying pressure to the Zn tip, it became possible to plate the Al specimen without zincate pretreatment. However, an anomalous deposition of Ni was sometimes observed around the Zn tip. This anomalous deposition was found to be formed at damaged areas such as the area to which the Zn tip was applied and the edges of the specimen. When these areas were coated, the time at which Ni deposition began was delayed and the distribution of Ni on the surface became uniform. Based on these results, the function of zincate pretreatment in electroelss Ni plating was considered.
The electrodeposition behavior of Ni-Mo alloy from a gluconate bath was investigated by a Hull cell test. The Mo content and deposition current efficiency of the Ni-Mo alloy were also measured as a function of the plating conditions of bath pH, deposition current density and bath ingredient concentrations. Smooth and bright Ni-Mo alloy was deposited at a relatively high deposition current efficiency (about 60%) from an ammonium-gluconate bath of above pH9. The higher the molybdate concentration in the bath, the higher the Mo content of the deposits. On the other hand, the Mo content of the deposits decreased with an increase in deposition current density and bath pH. The current efficiency of the Ni-Mo alloy deposits decreased linearly with Mo content. SEM observation revealed that the alloy deposits from the gluconate bath were smooth and compact with no cracks. Polarization curve measuremants and immersion tests of Ni-Mo alloy deposits were carreid out in solutions of both 1N HCl and 1N H2SO4. The results indicated that the Ni-Mo alloy had a higher self-passivation ability and lower corrosion rate than the conventional Cr plating deposits. A salt spray test showed the better corrosion resistance of the alloy deposits with the higher Mo content.
The electroless plating of a cobalt layer containing tungsten onto a copper substrate was investigated, using hydrazine as a reducing agent. The plating reaction was initiated by placing a strip of aluminium foil in contact with the substrate in the plating bath. Under optimized conditions, a uniform cobalt layer containing 0.9% tungsten was deposited with a deposition rate of 1.6μm h−1. As the concentration of tungstate in the plating bath was increased, the tungsten content of the resulting cobalt layer increased while the deposition rate decreased.