Abstract
Sulfuric acid and trivalent chromium ion were added to chromic acid solution and the cathodic polarization curve was varied with the reduction reaction of hexavalent chromium ion. With increases in trivalent chromium ion, the first peak current density on the cathodic polarization curve increased but the third peak decreased. With the addition of sulfuric acid, the first and third peek current densities showed behavior opposite to that when trivalent chromium ion was added. It is therefore considered that the amount of degradation of the chromium acid solution can be evaluated qualitatively by the behavior described. It is further thought that the formation of chromium oxide film was accelerated by an increase in trivalent chromium ion, while the presence of the SO42- ion of the sulfuric acid solution inhibited the formation of chromium oxide film. Thus, it seems that chromium deposition occurs initially by reduction of chromium oxide film, after which hexavalent chromium is continuously deposited by reduction due to the catalytic action of SO42-.
