ワット浴からのニッケルめっきに及ぼすホウ酸の影響
1993 年 44 巻 1 号 p. 39-43
詳細
1993 年 44 巻 1 号 p. 39-43
Investigations were conducted on variations in the pll of solutions in the vicinity of a copper substrate by means of micro-electrode plated with Sb, on the resistance between a copper substrate and a tip of Luggin capillary by means of current interrupter electrolysis, and on the partial current density for nickel deposition by means of atomic absorption analysis of the deposits. The results indicated that with increasing current density the action of boric acid in nickel deposition changed from that of pH buffer in solution to that of inhibitor of the hydrogen evolution reaction.
Variation in solution pH near the copper substrate in plating baths containing boric acid was always smaller than that in baths without boric acid, although the current efficiency of the former was lower than that of the latter at current densities below 1.0A/dm2. This effect is attributed to the pH buffering action of a complex formed between boric acid and nickel ion.
At higher current densities (3.0 to 12.0A/dm2), on the other hand, the partial current density for hydrogen evolution was depressed more than that for nickel deposition in the presence of boric acid, and the current efficiency for nickel deposition was eventually enhanced to ca. 100% with increasing current density. This effect is attributed to the adsorptive interactions of boric acid at the electrode surface. In the absence of boric acid, however, solution pH near the copper substrate increased to ca. 6.5 in a fluctuating manner, resulting in the deposition of a green-black thin film consisting of a mixture of Ni(OH)2 and Ni metal, the surface of which had many cracks, and the morphology of rock covered with moss.
