A defect associated with the use of the Sargent bath, a widely-used device for chromium plating, is the substantially lower current efficiency of chromium, compared to that of other metals. It has been reported that the use of a formic acid bath leads to the production of amorphous-structured chromium deposits with a higher current efficiency. However, it is difficult to use this process commercially, because of difficulties involved in maintaining the bath. In this paper, the concentration of Cr3+ ion in the vicinity of the cathode in a formic acid bath was estimated from the current density, the aging time of the bath and the rotating speed of the rotating disk electrode (RDE) apparatus. The results show that Cr3+ concentration plays the most important role in determining the appearance of the deposited metal. The effect of formic acid and sulfuric acid on the chromium deposit was investigated, and the optimum Cr3+ concentration in the vicinity of the cathode on the chromium deposition process was determined. Taking these results into account, the conditions required for obtaining a bright deposit with a high current efficiency at a high deposition rate could be predicted, resulting in a bright deposit with a current efficiency of 64.8% at a deposition rate of 17.1μm/min.
A new method using non-electrolytic deposition/stripping voltammetry was developed for determining trace amounts of chloride ion in the order of 0.1mg L-1 in copper electrolyte solutions. It was found, using a silver electrode as the working electrode, that when the electrode was immersed for a certain time in an agitated copper electrolyte solution containing a certain amount of Fe(III) ion, a quantitative amount of chloride ion could be spontaneously collected without applying electric potential. Then the deposited silver chloride on the silver electrode was stripped. One cycle of measurement of this method took approximately 10min, and the relative standard deviation of the measurements of 0.5mg L-1 chloride ion in a synthetic copper electrolyte solution was 2.0%(n=10). The effect of coexistent substances was examined. The measured concentration of chloride ion was influenced by changes of concentrations of copper (II) ion, sulfuric acid and iron(III) ion. Then, a calibration method using the standard addition method was examined. The time required for the whole procedure of the standard addition method was approximately 60min, and the relative standard deviation of the measurement of chloride ion in diluted copper electrolyte solution was 5.6% (n=6).
The relationships between the magnetic field dependence of the magnetoresistance effect and the film preparation conditions for composition-modulated Ni-Co-Cu films produced by the pulse control electrodeposition method were investigated. It was possible to produce multilayer films containing more than three layers composed of non-magnetic and ferromagnetic layers having different magnetic properties. A highly sensitive change of the electric resistance was obtained at a low magnetic field. The MR ratio observed in the film has maximum values of about 6% at 300K.