Abstract
An investigation was conducted into the chemical reaction in an interface layer consisting of three phases, which were metal, electrolyte, and air generated during zinc electroplating. The plating bath was a zinc sulfate solution of pH 4.0 and a SUS 304 metal rod that had had its surface oxidized in a 10 vol. % nitric acid solution was used as an electrode. The electrode, hung perpendicularly using an electronic balance, was partially immersed in the plating bath. The wetting behavior of the solution before electrolysis and the spreading wetting that occurred during zinc electroplating were evaluated in-situ as the variation of the loads using the electronic balance.
The wetting of the SUS 304 electrode by the solution decreased significantly as a result of the oxidation of its surface by the nitric acid solution. On the other hand, the as-deposited zinc enhanced the wetting of the electrode surface and resulted in spreading wetting by the solution. The developing solution proceeded up along the sidewall of the SUS 304 electrode, reaching a height of about 1mm above the plating bath during zinc electroplating. Hydroxide ions were formed by the reduction of oxygen that occurred in the upper region of the wetting film, and zinc electroplating occurred preferentially in the lower region of the SUS 304 electrode close to the counter electrode. A white precipitation was formed spontaneously in the intermediate region of the thin film. This precipitate was zinc hydroxide produced by the reaction caused between hydroxide ions moving down from the upper side and zinc ions supplied up through the thin film from the plating bath.
