Research On The Cyanide-Free Silver Electroplating Process

Traditional silver electroplating contains a high concentration of highly toxic potassium cyanide.Potassium cyanide poses a great threat to people and the surrounding natural environment whether it is produced,stored,transported or used.In response to green development,in recent years,domestic and foreign scientific researchers have carried out low-cyanide and non-cyanide-free silver electroplating process research and have made certain progress.However,compared with cyanide silver plating in terms of bath performance,coating performance and process performance,there is still a certain gap;at the same time,most of the cyanide-free silver plating systems cannot achieve direct conversion on the basis of cyanide silver plating solution,resulting in waste.In view of the above problems,using M-complexing agent as the main complexing agent,the free cyanide-free silver plating（LCN silver plating）and cyanide-free silver plating（NCN silver plating）processes were studied,and the existing cyanide silver plating The feasibility of system direct conversion,the specific research content is as follows:1)Determine the process parameters of LCN silver electroplating.With silver potassium cyanide（K[Ag（CN）₂]）as the main salt,complexometric titration and Hall cell experiment were used to screen and determine the composition and content of complexing agent,silver ion,conductive salt and displacement agent,and single factor experiment to determine the process temperature,pH value and current density range,the process parameters are as follows:20-30 g/L silver,150-230 g/L M-complex,10-40 g/L KSCN,0-5 g/L KOH,30 m L/L BAg-2002 silver plating brightener,temperature20-30℃,pH 12-13,can use cathode current density 0.1-2.5 A/dm².The current efficiency,dispersion ability and leveling ability of the plating solution system,the discoloration resistance,contact resistance,weldability and potassium sulfide resistance of the silver layer are basically close to those of the cyanide system.At the same time,the process stability is good,and it can be applied to actual production.2)Determine the process parameters of NCN silver electroplating.On the basis of LCN silver electroplating,With the M-complex as the main complexing agent,cyanide-free silver salt was screened,the plating solution formula was optimized,the auxiliary complexing agent and shielding agent were introduced,and single factor experiment to determine the process temperature,pH value and current density range,the process parameters are as follows:20-30 g/L silver（AgSCN）,200-250 g/L M-complexing agent,40-60 g/L potassium citrate,20-30 g/L K₂SO₄,5-10 g/L EDTA,30m L/L BAg-2002 silver plating brightener,Temperature 20-30℃,pH 12-13,can use cathode current density 0.3-2.3 A/dm².Compared with the current commercially available non-cyanide silver plating system,the plating solution system can increase the current density range by more than 1 time,and the brightness of the plating layer is better.