Experimental Study Of Environmentally Trivalent Chromium Plating

Chromium eletroplating, one of the most widely used industrial eletroplating technologies, has numerous applications in daily life and industrial fileds. The traditional plating process is completed by the hexavalent chromium plating method. However, hexavalent chromium plating has shortcomings such as low current efficiency, high energy consumption, and poor coverage capacity. In addition, hexavalent chromium is extremely harmful to the health of operating workers and environment. Therefore, it has become an inevitable trend that a new chromium plating technology will replace the traditional way.In this thesis, ammonium formate and ammonium oxalate are compounded as a complexing agent of the chloride system eletroplating solution for eletroplating trivalent chromium. The complete system has generally overcome the shortcomings of the hexavalent chromium plating technology illustrated above, with the superior performances including low toxicity, environment friendly, free from current disruption, feasibility at room temperature, etc. The experimental results show that the system used in the metal surface plating can achieve a chrome layer of bright appearance, large adhesion force and good corrosion resistance, which could basically meet the requirements for decoration and other practical use.The main work of this thesis includes the following three parts:(1) Trivalent chromium eletroplating on metal surfaceAmmonium formate and ammonium oxalate are compounded as a complexing agent of the chloride system eletroplating solution for eletroplating trivalent chromium on copper and 45 steel. Small tank experiments are conducted using the orthogonal test method with the thickness of the chrome layer taken as the assessment indicators and the optimal selection of the four process parameters, including concentrations of the two complexants in plating solution, cathode current density and plating time. Then good plating process conditions are obtained by further considering the effect of pH value and temperature of plating solution on the coating appearance. With the application of the optimized process conditions, chrome layers with bright appearance, uniform density, high purity, good adhesion and corrosion resistance on metal surface are achieved.(2) Electroless copper plating on non-metallic surfaceFormaldehyde-potassium sodium tartrate is used as plating bath to plate copper on non-metallic surface such as nylon, phenolic resins, and glass. The four parameters, which consist of pH value of the plating bath and concentrations and of the copper sulfate solution, potassium sodium tartrate solution and formaldehyde solution, are optimized with the plating rate taken as the assessment indicator. An evenly distributed, bright red-colored copper coating with good electrical conductivity and leakless plating can be achieved under the optimal process conditions. The experimental results show that the adhesion force of the copper coatings on nylon and phenolic resins surfaces are larger than that of glass surfaces.(3) Trivalent chromium eletroplating on non-metallic copper-plated part surfaceBased on the previous research in this paper, trivalent chromium eletroplating on the copper plated nylon and phenolic resins non-metallic surfaces were conducted, and the influence of current density on the appearance of the coating was investigated. Several improvement methods are proposed to enhance the adhesion force to overcome the weak adhesion of the coatings.