The gold-plated layer has good ductility, easy polishing, high temperature resistance and good discoloration resistance. Gold plating on the silver layer can prevent silver from discoloring; Gold alloy coating can present a variety of colors, so it is often used as decorative coating, such as plating jewelry, watch parts, works of art and so on.
The silver-plated layer is easy to polish, has strong reflection ability and good thermal, electrical and welding properties. Silver coating was originally used for decoration. In electronic industry, communication configuration and instrument manufacturing, silver plating is widely used to reduce the resistance of metal parts and improve the welding ability of metals. In addition, metallic reflectors in reflectors such as searchlights also need silver plating.
Electroplated silver coating is used to prevent corrosion and increase conductivity, reflectivity and elegance. Widely used in electrical appliances, instruments, meters, lighting appliances and other manufacturing industries. Electrical appliances, instruments and other industries also accept cyanide-free silver plating. Thiosulfate, sulfite, thiocyanate and ferrocyanide are used in electroplating solution.
In order to prevent the discoloration of silver coating, it is usually necessary to carry out post-plating treatment, which is usually immersion, chemical and electrochemical passivation, precious metal or several metal coatings or surrounding coatings.
Extended data:
Silver plating first started in 1800, and the first patent for silver plating was 1838, which was put forward by Elkington brothers in Birmingham, England. The plating solution used is alkaline cyanide plating solution, which is very similar to the alkaline cyanide gold plating system they invented. For more than a century, the basic formula of silver plating solution is not much different from that of that year, but the concentration of silver coordination ions is increased to achieve the purpose of rapid silver plating.
The main disadvantage of cyanide-based electroplating solution in the past was its low current density. Now this problem has been solved. High-efficiency silver plating can make the current density as high as 10A/dm, and bright silver plating can reach 1.5 ~ 3a/dm. The electroplated surface is smooth, and it can be plated thick without polishing. In recent years, high-speed selective silver plating of electronic components has developed rapidly, such as selective silver plating of lead frames, which adopts spraying method.
The current density used is as high as 300 ~ 3000 A/dm, and the concentration of silver potassium cyanide [KAg(CN)2] in the plating solution is as high as 40 ~ 75 g/L. Using platinum or platinum-plated titanium anode as anode, a silver layer of about 4 ~ 5 microns can be plated in 1s, which can meet the requirements of bonding silicon wafer and silver pad with aluminum wire.
Using carbon disulfide as brightener can not get a completely bright silver layer, and it will take some time to take effect when it is added to the plating solution. It is estimated that the real brightener is substituted urea, thiourea, guanidine, sulfide, cyanamide and some compounds in other sulfides generated by the reaction of carbon disulfide with CN- in the plating solution.
Baidu encyclopedia-silver plating
Baidu encyclopedia-gilded