Why are reed contacts plated with rhodium or similar materials?

Reed contacts are often plated with rhodium or similar materials primarily to prevent welding. In electrical applications, reed contacts are utilized to open or close circuits based on the proximity of a magnetic field. Over time and with repeated use, the contacts can experience wear or degradation, which could lead to them fusing or "welding" together under certain conditions, such as with high current levels. Plating with materials like rhodium helps to create a more resistant surface that can withstand the physical and thermal stresses involved in switching, effectively reducing the potential for welding. This enhances the reliability and longevity of the reed switch in its applications.

Other choices might suggest benefits such as aesthetic improvement or durability enhancement; however, the primary focus of rhodium plating in this context is specifically to mitigate the welding issue, thereby ensuring that the contacts function as intended without unintended sticking.