Studies On Preparation Of Silver Deposition And Mechanism Of Thiosulphate Electrodeposition Silver

Silver has good electric conductivity and solderability. In view of their excellent properties, silver is a metal electroplated for a wide variety of applications both decorative and functional. In the present work, thiosulphate silver electrodeposition bath was choosed as the research bath.To improve the faults of Anode passivation and silver deposite was not bright, anodic passivation inhibitor and brightener were studied. The composition and technological parameter of thiosulphate silver electrodeposition bath were optimized. The impacts of pulse plating process on the anti-sulfide corrosion and conductivity were researched. The electrodeposition process from thiosulphate silver electrodeposition bath and the influence of brightener on the silver deposition mechanism were studied. The results showed:The composition of thiosulphate silver electrodeposition bath as follows:AgNO345g/L, K2S2O545g/L, Na2S2O3·5H2O250g/L, CH5N3OS0.6-0.8g/L, brightener40mol/L, pH6-7and temperature10-30℃. the silver deposition of10μm can be obtained when the duty cycle5%, the pulse width2ms, the pulse average current density0.6A/dm2for30min. the silver deposition can not discoloration immersed in0.1mmol/L Na2S solution in5minutes,. The Surface contact resistance of3mm was17μΩ. It has been found by examinations on dispersing power and throwing power of bath and anti-sulfide corrosion and conductivity of silver deposition that this technics has the same or better effects than cyanide techics.In thiosulphate silver electrodeposition system, the grain size of silver deposition from80nm divided into50nm by brightener, aminothiourea can restrain the anode passivation, black precipitation was easily produced when the content of potassium pyrosulfite was lower than35g/L, the content of Sodium subsulfite was lower than150g/L or pH was lower than4, XRD analysis indicats that black precipitation may be Ag2S or S. The pulse electroplating process easier to get crystallization meticulous, grain sleek, uniform distribution of silver deposition than direct current deposition process. Increase the average current density and pulse width can enhance deposition overpotential, increase the duty cycle can cause strong cathode concentration polarization. The results of CV and Cathodic polarization curves indicated that the deposition of silver is a diffusion-controlled and reversiable growth process.It also can be observed from CV curves that a typical hysteresis loop existed, Silver complexation ion is Ag(S2O3)23-in solution. The results of CV and Impedance indicated that the brightener increases the reaction of bath resistance, reduces the cathodic current density in the regionof the peak and moves the nucleation loop to the negative direction. The results of chronoamperometric indicated that electrodeposition process of silver at GC electrode belongs to a three-dimensional progressive nucleation mechanism and the brightener does not change the nucleation mechanism, but inhibits the crystal epitaxial growth. and increases the nucleation rate constant persite and the saturation number density of nuclei.