| Silver is the metal with the best electrical and thermal conductivity,and has good ductility.It is widely used in the fields of electronics,communications and decoration.And silver is one of the earliest metals used in industrial electroplating applications.The cyanide silver plating process has a history of nearly 200 years.So far,about 90% of the silver plating production lines still use toxic cyanide systems.However,the silver plating liquid used in this system has obvious characteristics,namely,extremely high toxicity,high cost of waste liquid treatment,and serious pollution to the environment.Due to the increased environmental awareness of the public in the international arena,this situation has created an increasingly urgent need for a new process of electroless silver plating.In this paper,by studying several cyanide-free silver plating systems,5,5-dimethylhydantoin(DMH)was selected as the main complexing agent for silver ions in the plating solution,and niacin(NA)as the auxiliary complexing agent.Brighteners and surfactants,and the use of scientific methods to optimize current density,temperature and p H process parameters to obtain a cyanidefree silver plating process formula.In characterizing the microscopic morphology and composition elements of the coating,two techniques are commonly used,namely SEM and energy spectroscopy.In addition,in order to explore the degree of the influence of additives and temperature on the electrocrystallization mechanism and explore the correlation of silver on the surface of the glassy carbon electrode The electrodeposition mechanism of this study is mainly completed by potential step experiment and cyclic voltammetry experiment.Combined with single-factor experimental analysis,the combined additives ZY-1 and ZY-2were developed.The formulation and process conditions of the plating solution of the system were determined by a large number of Hull cell experiments: silver nitrate 25～50 g / L,5,5-II Methylhein40～110 g / L,nicotinic acid 15～25 g / L,potassium carbonate 80～120 g / L,potassium hydroxide35～75 g / L,ZY-1 0.1～0.5 g / L,ZY-2 0.2～1g / L,p H = 8～12,temperature 40～60 ℃.The data of the non-cyanide silver plating bath in terms of dispersion ability,deep plating ability,bath current efficiency,etc.are 44.8%,98%,and 99%,respectively.At the same time,this plating solution has the advantages of high stability,easy adjustment,and no need for pre-silver plating treatment.In addition,it has better performance in resistance to discoloration,welding,and bonding.Regarding the nucleation mechanism of Ag electrodeposition on the glassy carbon electrode(GCE)surface,this study mainly uses the SH classic theoretical model,potential steps and cyclic voltammetry.The results obtained show that the negative shift of the step potential changes from-750 m V to-825 m V.In this process,the electrodeposition of Ag on the surface of GCE is irreversible.Silver is not affected by both additives and temperature during electrocrystallization.By observing the initial silver deposition,the mechanism of three-dimensional instantaneous nucleation can be verified.In addition,the additives ZY-1 and ZY-2 have a very good polarization effect on the plating solution.The polarization effect in the low current density area is obvious,which is beneficial to the distribution of the plating layer.After the passivation of the organic compound PMTA +benzotriazole,this process significantly improves the anti-discoloration ability of the silver coating,and the anti-discoloration ability is increased by 30%.The self-corrosion current density is reduced to 1/10,and the corrosion resistance is significant improve.As a new type of complex coordination system non-cyanide silver plating process,compared with cyanide silver plating,the raw materials are cheap and readily available.It is suitable for various copper alloy non-cyanide silver plating processes,which is an alternative to promoting non-cyanide silver plating.The application of silver cyanide plating in aviation enterprises is of great significance. |
