Contacts, meaning mechanical contacts here, are a major part of most electronic products. Even if there is no mechanical switch anymore, you still have the contact between the plug and the outlet, and/or the contact springs for the batteries.
Contacts include the following items:
- Switches, plugs, relays, connections to removable parts (batteries, light bulbs, ...), pantographs (the thing on top of a locomotive), "brushes" (for motors), and so on.
- Contacts are also the components or materials that often cause trouble. Contacts or switches are often the first components to break, and thus a nuisance to consumers like you and me.
There are many specific requirements for contact materials:
- Small contact resistance (it is never zero).
- No sticking or welding under load.
- No abrasion under load.
- No intermixing of materials.
- No wearing and tearing.
- Suitable mechanical properties, e.g. good elasticity (forever) for switches.
There are specific materials and group of materials generally favored for contacts:
- C (graphite in many forms) for pantographs and whenever you want to draw a big current.
- Cu, Ag, Au.
- Ru, Rh, Pd, Os, Ir, Pt.
- Mo, W.
- An example of Ag-based contact materials can be found in the link.
- For contact applications we find expensive materials, because in many applications only small quantities are needed and the inertness of noble metals is what counts.