2000 年 51 巻 7 号 p. 724-728
A zinc chloride plating bath containing acetic acid as an alternative buffer in place of boric acid has a wide range of current densities and gives off a bright appearance. The dissolution of a steel substrate in this bath is promoted because of the bath's relatively low pH value of 4. In this paper, the influence of iron ions on zinc plating and their inhibition have been investigated.
Iron ions refined the grain size of deposits from a basic bath without brighteners. In a bath containing brighteners, when iron ions accumulated to more than 0.2g/L, the current range for brightness narrowerd. This result is due to iron ions that were reduced and codeposited in the zinc film; when the iron contents of the film exceeded about 0.6wt%, the grain size became coarser.
The pH value in which iron hydroxide is precipitated in the bath with acetic acid is higher than 6 because of the complexing effect of acetate: thus, the elimination of iron ions is not readily accomlished. However, the codeposition of iron was inhibited by adding quadrol or gluconate to the bath and the current range for brightness was restored to a certain extent.