ASTM B781-93a(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B781 − 93a (Reapproved 2012)
Standard Guide for
Silver-Cadmium Oxide Contact Material
This standard is issued under the fixed designation B781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope relays and contactors for switching lamps, motors and resistive
loads. Silver-cadmium oxide is a composite material consisting
1.1 This guide provides guidelines for users and manufac-
of a metal matrix, silver, with a metal oxide, cadmium oxide,
turers of silver-cadmium oxide material produced in strip, rod,
dispersed throughout the matrix. Compositions of up to 30 %
wire, and part form for electrical contact applications.
cadmium are made, but most applications use silver-cadmium
1.2 This standard does not purport to address all of the
oxide in the range of 10 to 15 % cadmium oxide by weight.
safety concerns, if any, associated with its use. It is the
Several different processes are used for manufacturing silver-
responsibility of the user of this standard to become familiar
cadmium oxide material and it should be understood that the
with all hazards including those identified in the appropriate
manufacturing method has an influence on the properties of the
Material Safety Data Sheet (MSDS) for this product/material
material such as arc erosion resistance, welding resistance, arc
as provided by the manufacturer, to establish appropriate
mobility and contact resistance. Since the performance of
safety and health practices , and determine the applicability of
contacts in a device is dependent on numerous factors outside
regulatory limitations prior to use.
the contact itself (opening speed, closing speed, contact
pressure, contact bounce and many more device parameters),
2. Referenced Documents
the guide cannot ensure performance in specific applications.
2.1 ASTM Standards:
4.2 Arc erosion resistance and welding resistance are im-
B311 Test Method for Density of Powder Metallurgy (PM)
proved by the addition of cadmium oxide to the silver matrix.
Materials Containing Less Than Two Percent Porosity
The contact resistance is raised by this addition but still is low.
B476 Specification for General Requirements for Wrought
Cadmium oxide and silver do not alloy so the silver matrix
Precious Metal Electrical Contact Materials
retains its high conductivity. Silver-cadmium oxide contacts
C914 Test Method for Bulk Density and Volume of Solid
are used in current ranges of a few amperes to several hundred
Refractories by Wax Immersion
amperes.
NOTE 1—Test Method B311 is applicable to fully dense forms.
4.3 Silver-cadmium oxide contact material is available as
Specification B476 is applicable to strip, rod, or wire only. Test Method
C914 is applicable to forms less than 99 % dense.
wire, silver-clad wire, sheet, strip, toplay, inlay and overlay
sheet or strip, discrete contact parts, brazed contact assemblies,
3. Terminology
solid and composite rivet contacts and clad contact tapes.
3.1 lot, n—(usage involving discrete manufactured parts)—
4.4 Materials with higher cadmium oxide contents have
allpartsofthesameform,anddimensions,fromthesamealloy
lower material costs but may have higher processing costs due
melt or batch of particulate (if manufactured by consolidation),
to lower formability.
processedunderthesameconditions,andsubmittedforinspec-
tion at the same time.
5. Manufacture
4. Significance and Use
5.1 Since the manufacturing method has a significant influ-
4.1 Silver-cadmium oxide is a popular contact material that ence on the properties and microstructure of silver-cadmium
has been used in a wide range of applications in switches,
oxide materials, it is important to understand some basic
information on the types of manufacturing. Silver-cadmium
This guide is under the jurisdiction of ASTM Committee B02 on Nonferrous
oxide manufacturing can be first divided in two categories:
Metals and Alloys and is the direct responsibility of Subcommittee B02.05 on
Internal Oxidation and Power Metallurgy.
Precious Metals and Electrical Contact Materials.
5.1.1 Internal oxidation means that the cadmium oxide
Current edition approved May 1, 2012. Published May 2012. Originally
particles are formed by diffusion of oxygen into the silver alloy
approved in 1987. Last previous edition approved in 2006 as B781 – 93a (2006).
DOI: 10.1520/B0781-93AR12.
to combine with cadmium atoms to form cadmium oxide
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
particles. This process can be further divided into the catego-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ries of post and pre-oxidized materials. The post-oxidized
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. process consists of performing the diffusion process after the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B781 − 93a (2012)
TABLE 1 Suggested Chemistries and Theoretical Densities
finished parts have been formed. The pre-oxidized process
consists of oxidation of slugs and the forming of wire or strip 86.5 Silver/
90 Silver/10 85 Silver/15 80 Silver/20
13.5
from the oxidized slugs and then forming the final parts. The
Cadmium- Cadmium- Cadmium-
Cadmium-
Oxide Oxide Oxide
cadmium oxide particle size distribution is dependent upon the
Oxide
grain structure of the silver cadmium alloy, any additive
Chemistry
Cadmium-Oxide 10.0 ± 1.0 13.5 ± 1.0 15.0 ± 1.0 20.0 ± 1.0
concentration, and oxidation conditions (for example,
weight %
temperature, oxygen partial pressure).
Silver weight % , 89.0 85.5 84.0 79.0
min
5.1.2 For powder metallurgy silver-cadmium oxide, the
Other elements (see 6.2)
material is made from a blend of silver and cadmium oxide
Theoretical Densities at Nominal Composition:
powder or other cadmium compounds such as cadmium
Mg/m 10.2 10.1 10.1 9.92
troy oz./in. 5.37 5.32 5.30 5.23
carbonate, which can be thermally decomposed to cadmium
oxide in a subsequent step. There are two basic types of this
process, one in which the contacts are pressed and sintered and
repressed into the final shape, and the other where a billet is
a distinct brazable or conductive backing, such backing shall
made from blended powder which is then formed into strip and
not be considered to be included in the silver-cadmium oxide
wire and made into the final contact shapes.
material composition.
5.1.3 All of these processes have many variations.There are
also hybrid processes such as internally oxidized powders 6.2 Additives and Impurities:
which are then processed by powder metallurgy. The user
6.2.1 A wide variety of chemical additives have been made
should obtain the basic information as to the type of material to silver-cadmium oxide materials for processing and perfor-
mance purposes. The merits of these additions remain a point
being purchased.
of contention. Additionally, various impurities may remain in
5.1.4 For purposes of attachment to bare metal supports,
these materials from raw materials or processing which have
silver-cadmium oxide contact material is often produced with a
been found to be either detrimental or helpful depending on the
conductive or brazable layer of material or backing. Incorpo-
residual level and the individual application. Chemical require-
ration of such a layer is often an integral part of the silver-
ments for such elements and analytical methods to be em-
cadmium oxide manufacturing process.
ployed shall be mutually agreed to by the producer and user.
5.1.5 Silver-cadmium oxide materials vary from full theo-
6.3 No substantive change shall be made to additives or
retical density to about 95 % of theoretical density depending
impurities without notification to and approva
...