Study On New Environmentally Friendly Process And Kinetics Of Copper Electroplating From HEDP Aqueous Electrolyte

The alkaline cyanide bath for industrial copper plating was commonly used for bottom plating at the present time. Basic research and development of environmentally friendly non-cyanide alkaline bath for copper plating used as an alternative to cyanide copper plating bath had a very important scientific significance and practical value. This was not only propitious to cleaner production for electroplating industries and environmental protection, but also elimination of the industrial production public safety hazards. There were many research reports about the non-cyanide alkaline bath for copper plating these days. The HEDP aqueous copper electroplating electrolyte which was the ideal alternative to cyanide copper process had an excellent throwing power and good adhesion. There were still some problems for its practical application at the same time. Accordingly, the objective of this paper was to discuss the optimal bath composition and operating conditions of the environmentally friendly copper electroplating bath, as well as the electrode kinetics and the applications of the copper electrodeposition on the steel, aluminum alloy and zinc alloy die castings substrates.In this work, HEDP was used as copper ion complexing agent. Potassium carbonate was choosed as conductive salt. A detailed study was made about the process of copper electroplating by Hull test and square tank test. The results showed that dense copper coatings which had good adhesion to substrate were obtained by increasing the complexation ratio of HEDP with copper ion without any other additives. The optimal bath composition and operating conditions were as follows: Cu²⁺ 10g/L; HEDP 160g/L; K₂CO₃ 60g/L; pH 9.0; EHS 0.5ml/L; Temperature 50℃; Air agitation; Dk 2A/dm². The advantages of the bath were not only its simplicity but also its excellent throwing power and the quality of the deposits. The copper coatings obtained by the bath were dense, semi-bright, and had good adhesion to steel, aluminum alloy and zinc alloy die castings substrate.The electrochemical behavior and cathodic process kinetics of the alkaline HEDP aqueous copper electroplating electrolyte were investigated by many electrochemical techniques. The results showed that the main form of existence of complex ions CuY^2-complex ions was formed. The kinetics parameters of cathodic process were measured by cathodic polarization curves. The cathodic electrochemical behaviors of complex ions were an electrochemistry determinative step and irreversible process, according with Tafel equation. The electrochemical reaction was finished in one step. Complex ion did not undergo prepositive chemical transformation reaction while it was reduced. As a result, the cathode reduction mechanism may be described as follows: CuY^2- + 2e→Cu+Y^4-...