Investigation On Technology And Electrodeposition Behaviors Of Silver Electroplating Using Composite Complexing Agents Containing Hydantoin

For it's silvery white metallic luster, high electric conductivity, high thermal conductivity, high ductibility, high solderability, high anti-discoloration ability and chemical stability. Plating of silver is widely used in both electronic engineering and decorative fields. The traditional cyanide silver plating bath has good stability and excellent properties. Due to strong toxicity of the cyanide compounds, there are problems related to safety, environmental pollution and a large amount of cost for waste treatment. With more and more global environmental problems, environmental protections of plating field have also been put on the agenda,non-cyanide silver plating baths are strongly in demand.By comparative study on several non-cyanide silver electrodeposition baths, DMH was choosed as the main complexing agent in present non-cyanide silver electrodeposition baths. By optimizing auxiliary complexer and conductive salt, the optimized electrolyte composition was determined. The influence of bath composition and operation conditions on the qualities of silver platings, cathodic current efficiency, limited current density, deposition rate and surface morphology were investigated by single factor study. The results showed the concent of silver nitrate, complexing agents'content and mole proportion, temperature, pH, stirring process and current density have effects on plating layer quality.The optimized electrolyte composition is: silver nitrate: 12.5g/L, DMH:87.5g/L, pyridine carboxylic acid(acid amides):87.5g/L, potassium hydroxide:75g/L, potassium carbonate:100g/L, pH value:10¹1, temperature:60±2℃, rotating speed: 600 rpm, current density: 0.6⁰.9A/dm². Under the optimized bath composition and plating conditions, the performance of hydantoin based on bath is equal to cyanide bath, the platings obtained in optimized plating conditions possessed mirror bright, better anti-discoloration ability. The adhesion strength between the coated layer and the copper substrate is very high.The surface morphologies of silver platings were characterized by SEM, the crystal texture was studied by XRD. The results showed that the crystal size of metallic silver was small and the array of crystal was dense. The qualities of platings obtained in optimized hydantoin based bath were equal to those obtained in cyanide bath. The bath has good throwing power, covering power and stability. The mechanism of silver electrodeposition and the kinetics parameters of cathodic process were investigated by cyclic voltammetry and cathodic polarization curves. Kinetics parameters of cathodic process were studied by Tafel linear extrapolation and their vales are: j0=4.05×10^-3mA/cm²,α=0.2, k=1.17×10^-4cm/s, Ea=15.81kJ/mol. The results of electrochemical techniques showed that the optimized electrolyte of combinational system is stable in the range of electrodeposition region without any additional reaction. The cathodic process of silver electrodeposition is a diffusion-controlled and irreversible process. The presence of additive increased cathodic polarization, expanded current density range and improved the quality of silver platings and does not change crystalline state.