The function of rhodium plating
The chemical properties of rhodium are relatively stable, and it is difficult to react with sulfide and carbon dioxide in the air. At room temperature, it is insoluble in nitric acid and its salts, and even insoluble in water. It is more stable to various strong alkalis, but rhodium is soluble in concentrated sulfuric acid. The physical properties of rhodium are relatively good. In addition to good wear resistance and electrical conductivity, it has outstanding reflection ability, and its reflection coefficient can reach 80% (silver is 100%), and it can remain unchanged for a long time. Therefore, it is often used as an anti-silver discoloration coating. After testing, the 0.1um rhodium coating can protect the silver coating from discoloration for several years. The rhodium coating has very low contact resistance and high hardness, so it is often used as a coating for contact points.
The welding performance of rhodium is not very good, because the internal stress of the coating is relatively large. Rhodium plating technology began to be used in the United States in 1930, but it was mainly used for decorative coatings. Later, with the rapid development of the electronics industry, rhodium plating played an important role in preventing silver discoloration and electrical contact points. In recent years, rhodium plating has become more popular in the jewelry electroplating industry. Electroplating a layer of rhodium on the surface of silver jewelry can prevent silver from discoloration. The price is cheap and it can also show a platinum-like texture. Since the density of rhodium is much smaller than that of platinum, the cost of rhodium plating is a little lower than that of platinum plating.