ギ酸添加浴を用いた高効率高速クロムめっき II. 光沢クロムめっき形成に及ぼす電極表面の３価クロムイオン濃度の影響

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.