Active Standard ASTM B781 | Developed by Subcommittee: B02.05
Book of Standards Volume: 02.04
Historical (view previous versions of standard)
Significance and Use
Silver-cadmium oxide is a popular contact material that has been used in a wide range of applications in switches, relays and contactors for switching lamps, motors and resistive loads. Silver-cadmium oxide is a composite material consisting of a metal matrix, silver, with a metal oxide, cadmium oxide, dispersed throughout the matrix. Compositions of up to 30 % cadmium are made, but most applications use silver-cadmium oxide in the range of 10 to 15 % cadmium oxide by weight. Several different processes are used for manufacturing silver-cadmium oxide material and it should be understood that the manufacturing method has an influence on the properties of the material such as arc erosion resistance, welding resistance, arc mobility and contact resistance. Since the performance of contacts in a device is dependent on numerous factors outside the contact itself (opening speed, closing speed, contact pressure, contact bounce and many more device parameters), the guide cannot ensure performance in specific applications.
Arc erosion resistance and welding resistance are improved by the addition of cadmium oxide to the silver matrix. The contact resistance is raised by this addition but still is low. Cadmium oxide and silver do not alloy so the silver matrix retains its high conductivity. Silver-cadmium oxide contacts are used in current ranges of a few amperes to several hundred amperes.
Silver-cadmium oxide contact material is available as wire, silver-clad wire, sheet, strip, toplay, inlay and overlay sheet or strip, discrete contact parts, brazed contact assemblies, solid and composite rivet contacts and clad contact tapes.
Materials with higher cadmium oxide contents have lower material costs but may have higher processing costs due to lower formability.
1.1 This guide provides guidelines for users and manufacturers of silver-cadmium oxide material produced in strip, rod, wire, and part form for electrical contact applications.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices , and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
B311 Test Method for Density of Powder Metallurgy (PM) Materials Containing Less Than Two Percent Porosity
B476 Specification for General Requirements for Wrought Precious Metal Electrical Contact Materials
C914 Test Method for Bulk Density and Volume of Solid Refractories by Wax Immersion
ICS Number Code 77.150.70 (Cadmium and cobalt products)