Electrochemical Studies on Corrosion Resistance of Nickel-Chromium Electroplates

Abstract

The electrochemical studies have been made in order to know the corrosion resistance of nickel-chromium (Ni-Cr) electroplates. It was found that chromium plate tends to become passive at less noble potentials than the nickel in acid sulfate solution, and the rate of dissolution of the former is very small compared with the nickel electroplate.
The nickel corrodes somewhat more rapidly than it would in the absence of chromium, because of the galvanic cell created by chromium covering to nickel. In the initial stage of the corrosion reaction, the rate of attack of the nickel was found to be affected by the numbers of the defects of chromium coatings and also by the nature of nickel coating.
The microscopic examination of the cross section of Ni-Cr electroplate which have been subjected to the electrochemical measurement showed that corrosion pits in the nickel layer were distributed rather uniformly in the case of microcracked chromium, but randomly in the conventional chromium plate.
The corrosion resistance of the double-layer nickel can be explained by the fact that the sulfur-containing nickel plated on the sulfur-free nickel will undergo preferential attack and is effective in the retardation of the rate of penetration into the double-layer nickel coatings.