### 2.3.2 Contacts

| 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.

© H. Föll (Advanced Materials B, part 1 - script)