A Novel Chromium Plating from Trivalent Chromium Solution

Abstract

Chromium deposition process from a novel Cr(III) solution based on a couple of carboxylic acids as complexing agents has been described. This process not only produce a bluish-white color of deposit visually indistinguishable from that of Cr(VI) plating, but also maintain a constant deposition rate over a prolonged period. It was found that the nature of a Cr(III) complex had a great influence on the deposition process including the deposit color, deposition rate and a sustained deposition process. It is proposed that an excessive hydrogen evolution on overall deposition process is detrimental to the deposit color and deposition rate because it causes a rapid rise of pH and thus the precipitation of a series of Cr(III) hydroxides on the cathode. The mixed Cr(III) complex obtained by the couple of carboxylic acids can promote chromium deposition reaction, suppress a rapid rise of pH in the cathode layer, and keep a sustained deposition process at lower current densities. The effects of solution constituents and compositions, pH and temperature on the deposit color, deposition rate and surface morphology have been investigated and discussed.