No.3（2000）4.Investigation of substitution agents in place of boric acid in a nickel plating bath

Tadashi DOI, Kazunari MIZUMOTO, Masashi KAYASHIMA, Shin-ichi TANAKA

The role of individual components of a Watts bath has been investigated using a Hull cell test in order to research the possibility of substitution agents in place of boric acid. Boric acid inhibits hydrogen evolution as a side reaction for nickel deposition Hydrogen evolution causes a rise in the pH of the plating bath, resulting in the appearance of burns or the precipitation of nickel hydroxide on the plated surface. Therefore, the difference in pH before and after a Hull cell test is one of the key factors in judging the performance of a nickel plating bath containing substitution agents such as pH buffers. Buffers like citric acid and nickel citrate are effective in that a difference in pH is not observed during the Hull cell test and a satisfactory appearance, as given by boric acid, is obtained. These agents or a complex with nickel ions and the agents is readily adsorbed on the surface of the cathode, resulting in the inhibition of the hydrogen evolution reaction. Citric acid and nickel citrate are possible substition agents in place of boric acid.

Keywords
Nickel plating, Boric acid, pH buffering action, Citric acid, Hull cell test, Watts bath

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