Silver’s high thermal and electrical conductivity make it an ideal contact material for contact applications—in fact, it has the highest electrical and thermal conductivity of all the metals. Pure silver, however, is susceptible to mechanical wear; it has a low softening temperature; it is susceptible to welding; and it can cause total failure in switching devices. Silver, therefore, is often mixed with other metals to create various silver-based contact materials. Different contact applications have different contact material requirements, and for that reason, there are a variety of different silver-based contact materials. Each silver-based contact material has its distinct advantages. Knowing the intended application of the silver-based contact materials will give you the opportunity to select the most advantageous one.
Properties of Silver
Silver-metal oxide materials, such as silver-cadmium oxide (Ag-CdO) and silver-tin oxide (Ag-SnO2), have very good contact and switching properties—they’re highly resistant to welding, low contact, and high arc erosion. For this reason, silver-metal oxide materials are widely used for various applications, including relays, appliances, protective devices, sliding electrical contact devices, and silver contact tips. Each silver-metal oxide material has its own distinct advantage over the other.
Traditionally, Ag-CdO has been the go-to silver electrical contact for a multitude of applications. As stated earlier, it has great contact and switching properties and is very often used for sliding electrical contact devices and silver contact tips. Indeed, the process in creating larger silver contact tips from Ag-CdO presents substantial economic advantages over using Ag-SnO2. Ag-CdO’s contact properties can be influenced by using different silver powders and additives—it is this versatility that has made Ag-CdO one of the most widely-used silver electrical contacts.
Recently, however, Ag-SnO2 has begun replacing Ag-CdO. Ag-SnO2 has been shown to have less toxicity than Ag-CdO. Additionally, Ag-SnO2 often shows improved contact and switching properties over those of Ag-CdO. Ag-SnO2’s contact properties can also be influenced during the manufacturing process, so it can also be quite versatile; however, the process of making complex forms of electrical contacts—such as silver contact tips—is more economically efficient with Ag-Cd alloy versus Ag-SnO2.
Each silver-based contact material has its advantages, and knowing the intended application for the silver-based contact material is crucial.