The Development Of A Trivalent Chromium Electroplating Process

Trivalent chromium plating technology got more and more attention due to its environmental advantage and higher current efficiency compared to hexavalent chromium plating technology.Although a lot of progress have been made in trivalent chromium plating technology development,there are still many problems in industrial application.The main purpose of this study is to develop a trivalent chromium process which can be used in industry as an alternate for hexvalent Cr coating process.By a large number of exploratory experiments,a trivalent chromium plating bath system(sodium formate-ure-additive A system)has been finally selected for further optimization study.This bath system has good plating ability.Excellent Cr coating can be successfully made in the bath under proper plating conditions.In the bath solution,chromium sulfate was used as the source of Cr,HCOONa was used as main complex agent,agent A and urea were used as auxiliary complex agents.The relationships between the current efficiency and the bath temperature,the bath pH value,the plating time,the current density were studied.The best cathode current efficiency of the bath is 19%.3.5?m thick Cr coating can be made.Observation by scanning electron microscope showed that the coatings consist of tiny Cr grains which are in the form of corn grain.The EDS analysis shows that the coating is a chromium coating containing a small amount of C-elements and O elements.X-ray diffraction(XRD)analysis showed that the Cr coating is single metal Cr phase.The result of Cr coating properties examination showed that the smooth and meticulous coating has good adhesion with the substrate.The bath solution performance tests showed that the dispersion capability,the coverage capability and the stability of the bath system are good.The trivalent chromium plating process can be used as a decorative Cr coating plating technology.