ASTM B844-98(2004)
(Guide)Standard Guide for Silver-Tin Oxide Contact Material
Standard Guide for Silver-Tin Oxide Contact Material
SIGNIFICANCE AND USE
The methods for manufacture (proprietary or otherwise) of these materials vary significantly among suppliers, and these methods influence such properties as arc erosion, contact resistance, and tendency to weld in service. Since the performance of contacts in a device depends on numerous factors outside the contact itself (opening speed, closing speed, contact pressure, contact bounce, environmental variations, assembly technique and variations, etc.) this guide cannot ensure performance control in the application. As part of the qualification on initial samples it is recommended that the user electrically test the materials in a functional manner for all devices applicable to the material’use. This guide will provide a means for the contact manufacturer and contact user to reach agreement on the details of material to be supplied for a specific use and how to provide reasonable assurance that future lots will be similar in properties and microstructure to the initial test of sample contacts supplied.
SCOPE
1.1 This standard provides guidelines for users and manufacturers of silver-tin oxide material produced in strip, rod, wire, and part form for electrical contact applications.
1.2 Silver-tin oxide refers to contact material containing silver, tin oxide, and other metal oxide which may be used for either improving the processing or performance of the material.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.4 It is the responsibility of the user to become familiar with all hazards including those identified in the appropriate Material Safety Data sheet for this product/material or provided by the manufacturer.
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Standards Content (Sample)
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Designation:B844–98(Reapproved2004)
Standard Guide for
Silver-Tin Oxide Contact Material
This standard is issued under the fixed designation B844; 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 processedunderthesameconditions,andsubmittedforinspec-
tion at the same time.
1.1 This standard provides guidelines for users and manu-
facturers of silver-tin oxide material produced in strip, rod,
4. Significance and Use
wire, and part form for electrical contact applications.
4.1 The methods for manufacture (proprietary or otherwise)
1.2 Silver-tin oxide refers to contact material containing
ofthesematerialsvarysignificantlyamongsuppliers,andthese
silver, tin oxide, and other metal oxide which may be used for
methods influence such properties as arc erosion, contact
eitherimprovingtheprocessingorperformanceofthematerial.
resistance, and tendency to weld in service. Since the perfor-
1.3 This standard does not purport to address all of the
mance of contacts in a device depends on numerous factors
safety concerns, if any, associated with its use. It is the
outsidethecontactitself(openingspeed,closingspeed,contact
responsibility of the user of this standard to become familiar
pressure, contact bounce, environmental variations, assembly
with all hazards including those identified in the appropriate
technique and variations, etc.) this guide cannot ensure perfor-
Material Safety Data Sheet for this product/material as pro-
mance control in the application.As part of the qualification on
vided by the manufacturer, to establish appropriate safety and
initial samples it is recommended that the user electrically test
health practices, and determine the applicability of regulatory
the materials in a functional manner for all devices applicable
limitations prior to use.
to the material’s use. This guide will provide a means for the
2. Referenced Documents contact manufacturer and contact user to reach agreement on
the details of material to be supplied for a specific use and how
2.1 ASTM Standards:
to provide reasonable assurance that future lots will be similar
B311 Test Method for Density of Powder Metallurgy (PM)
in properties and microstructure to the initial test of sample
Materials Containing Less Than Two Percent Porosity
contacts supplied.
B476 Specification for General Requirements for Wrought
Precious Metal Electrical Contact Materials
5. Materials and Manufacture
NOTE 1—Test Method B311 is applicable to fully dense forms. Speci-
5.1 Various processes may be utilized to produce silver-tin
fication B476 is applicable to strip, rod, or wire only. Test Method is
oxide contact materials. Internal oxidation of a silver-tin alloy
applicable to forms less than 99 % dense.
is a viable method. However, if oxidized at relatively low
pressures, a binary silver-tin alloy develops a stable layer of tin
3. Terminology
oxide at the surface which inhibits further oxidation of the
3.1 Definitions of Terms Specific to This Standard:
material. Because of this phenomenon, usually at least a third
3.1.1 lot—(usage involving discrete manufactured parts)—
element (such as indium) is added to the alloy in order to
allpartsofthesameform,anddimensions,fromthesamealloy
promoteinternaloxidation.Oxidationmaybecarriedoutunder
melt or batch of particulate (if manufactured by consolidation),
elevated oxygen pressure and also at various temperatures;
oxidation conditions determine size and distribution of the
This guide is under the jurisdiction of ASTM Committee B02 on Nonferrous
resultingoxideparticles.Othermanufacturingprocessesutilize
Metals and Alloys and is the direct responsibility of Subcommittee B02.05 on
powder metallurgical techniques. Silver- and tin-oxide pow-
Precious Metals and Electrical Contact Materials.
ders may be blended and consolidated by heat or pressure, or
Current edition approved May 1, 2004. Published May 2004. Originally
both, into wire or strip suitable for further processing, or may
approved in 1993. Last previous edition approved in 1998 as B844 – 98. DOI:
10.1520/B0844-98R04.
be blended and sintered directly into contacts. Methods that
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
can be used to prepare silver- and tinoxide powder mixtures
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
include either coprecipitation or sequential precipitation of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. silver and tin compounds from aqueous solutions, coating of
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B844–98 (2004)
tin-oxide particles by precipitation of silver from an aqueous remain in these materials from raw materials or processing
solution, and powder atomization of a silver-base alloy fol- which have been found to be either detrimental or helpful
lowed by internal oxidation of the atomized powder. depending on the residual level and the individual application.
5.1.1 Silver-tin oxide materials are used in various tempers Chemical requirements for such elements and analytical meth-
dependent on the attachment and fabrication process utilized. ods to be employed shall be mutually agreed upon between the
5.1.2 For purposes of attachment or device performance, producer and the user.
silver-tin oxide contact material is often produced with a 6.2.2 It should be noted that the operating characteristics of
conductive or brazable layer of material or backing. Incorpo- silver-tin oxide materials with different additives may be very
ration of such a layer is often an integral part of the silver-tin different. Certain operating characteristics such as welding
oxide manufacturing process. resistance, electrical erosion, and others may improve or
5.1.3 Silver-tin oxide materials vary from full theoretical degrade as a result of additives. As a result of differences in
density to about 95 % of theoretical density depending on the t
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