Application of precious metals in electric light source products
Gold, silver, platinum and palladium are all precious metals that are most stable to various chemical reactions. Gold and silver are not very difficult to melt. The conductivity of gold is second only to silver and copper, and it does not oxidize at high temperatures in the air. Therefore, gold is sometimes plated on the pins for protection and good conductivity.
Silver has the best conductivity and does not oxidize at room temperature. Therefore, some light source components are often plated with a layer of silver to provide good conductivity and protection. Silver paste is often used to apply to the surface of glass or ceramics to obtain a conductive coating.
Gold and silver can both be dissolved in aqua regia and potassium cyanide. In addition, silver can also be dissolved in nitric acid. Platinum has high chemical stability and excellent ductility. In a vacuum, it evaporates little, and its linear expansion coefficient matches that of soft glass. Therefore, platinum can be hermetically sealed with soft glass. Platinum can also be used as a thermal insulation coating and conductive coating for discharge lamps, and platinum wire can be used as an electric heating element or thermocouple. Due to the high price and small quantity of platinum, it is rarely used in electric light sources.
Palladium is even less used in electric light sources. Hydrogen can diffuse through palladium, thereby removing gas impurities in the hydrogen. Palladium can be used to deliver high-purity hydrogen into devices (such as hydrogen lamps).