Research On Electrochemical Polishing And Anti-tarnish Techniques Of Silver

Silver is used widely in varied areas,such as coins,art,electronic industries and avionic device,for its brilliant appearance and excellent characters.Silver is sensitive to sulfide,so it will tarnish when there is sulfide in air.To improve the appearance and character of silver,it is necessary to do some surface techniques to silver like polishing and anti-tarnish techniques.The technology of electrochemical polishing silver is researched in the paper.The best polishing technique is studied by orthogonal test.The optimal polishing of silver technique is 200g/L KSCN,30mL/L H₃PO₄,100mL/L polyethylene glycol,4g/L methanesulfonic acid, operating voltage is 10V,operating temperature is 30℃and polishing time is 1～2min.The factors which affect the polishing are also researched.It shows that,(1)samples after polishing glisten well as mirror.(2)samples are very clean and there is no reaction production and no electrolyte on the surfaces.(3)samples are flat and the roughness curve is near to the mirror's.The electrolyte is containing simply and low costs.It dose not contain CN^- and is harmless to environment.Based on above,the anti-tarnishing technique of silver is studied.The optimal passivation technique of silver is 2g/L benzotriazole,2g/L 2-mercaptobenzothiazole,some potassium hydroxide and ethanol,operating temperature is 50℃and operating time is 3min。Samples keep bright and clean after the passivation.The anti-tarnishing time of passivated sample in drop tests is more than 3 minutes.It is 5 times as the blank sample.The accelerated test also shows that passivation makes the better anti-tarnishing ability.The contact resistance has no big change before and after passivation.Polarization curves of silver before and after passivation show that,the passivation improved the anode reaction and node reaction,and enhanced the anti-tarnishing ability of silver。...