Study Of Chromium Plating Process In The Sulfate Solution For Trivalent Chromium

Chromium plating is one of the most broad technologies used in electroplating industry. The traditional chromium plating has carried by hexavalent chromium plating. As the ion of hexavalent chromium is virulent, it is harmful to workers and environment pollution. Therefore, we studied a kinds of trivalent chromium plating which is the sulfate solution and environmentally friendly.In this paper, TirEAC TCR-3000 series of trivalent chromium plating process was researched. Through the Hull Cell test and rectangular electrolyzer test, the factors of the effects on the coating were discussed, such as electroplating time, pH value, temperature, stirring method and cathode current density. Results showed that the thickness of coating increased with the electroplating time showing a trend by first-quick-then-slow down; when pH=3.5, the available thickness and bright coating appeared; the brightness of coating increased with increasing temperature; considering energy consumption,45℃was best without stirring; meanwhile, the operational current density was wide and the optimal condition was 4～6A·dm-2.Meanwhile, the properties of the trivalent chromium coating were were analysed such as adhesive force, corrosion resistance, crystalline structure, microstructure. Results showed that the adhesive force of trivalent chromium coating was very good; The corrosion potential of trivalent chromium coating was much higher than hexavalent chromium coating by Tafel curve test; the trivalent chromium coating was a chromium-iron coating with XRD, it was also one of the reasons it had good corrosion resistance; the corrosion current was a little bigger as it had many tiny pinholes on surface topography by SEM. In a word, the properies of trivalent chromium coating and hexavalent chromium coating were basically same.The effects of metal impurity ions on the coating in TCR-3000 chromium electroplating bath were discussed by Hull Cell test, and the treatment effects with a selective cation exchange resin on the bath including metal impurity ions were analysed. Experiment shows that when the concentrations of Cu2+, Ni2+, Zn2+ are 10 mg·L-1,50 mg·L-1,60 mg·L-1 respectively, the bath can be operated only at the toplimit of working current, so the concentrations are the tolerance of the bath of metal impurity ions. Meanwhile, the polluted bath was dealt with a selective cation exchange resin, then the concentrations of impurity ions were significantly decreased, and the bath can be operated normally.At the present, TirEAC TCR-3000 series of trivalent chromium plating has already put into production go into operation. The process can be used extensively in kinds of products which are decorative lighting, furniture, bathroom accessory, electrical equipment, technology of electronics industry, communication technology industry and so on.