ASTM B844-98
(Guide)Standard Guide for Silver-Tin Oxide Contact Material
Standard Guide for Silver-Tin Oxide Contact Material
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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Designation: B 844 – 98
Standard Guide for
Silver-Tin Oxide Contact Material
This standard is issued under the fixed designation B 844; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope processed under the same conditions, and submitted for inspec-
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
of these materials vary significantly among suppliers, and these
silver, tin oxide, and other metal oxide which may be used for
methods influence such properties as arc erosion, contact
either improving the processing or performance of the material.
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
outside the contact itself (opening speed, closing speed, contact
responsibility of the user of this standard to establish appro-
pressure, contact bounce, environmental variations, assembly
priate safety and health practices and determine the applica-
technique and variations, etc.) this guide cannot ensure perfor-
bility of regulatory limitations prior to use.
mance control in the application. As part of the qualification on
1.4 It is the responsibility of the user to become familiar
initial samples it is recommended that the user electrically test
with all hazards including those identified in the appropriate
the materials in a functional manner for all devices applicable
Material Safety Data sheet for this product/material or pro-
to the material’s use. This guide will provide a means for the
vided by the manufacturer.
contact manufacturer and contact user to reach agreement on
2. Referenced Documents the details of material to be supplied for a specific use and how
to provide reasonable assurance that future lots will be similar
2.1 ASTM Standards:
in properties and microstructure to the initial test of sample
B 311 Test Method for Density of Cemented Carbides
contacts supplied.
B 476 Specification for General Requirements for Wrought
Precious Metal Electrical Contact Materials
5. Materials and Manufacture
C 914 Test Method for Bulk Density and Volume of Solid
4 5.1 Various processes may be utilized to produce silver-tin
Refractories by Wax Immersion
oxide contact materials. Internal oxidation of a silver-tin alloy
NOTE 1—Test Method B 311 is applicable to fully dense forms.
is a viable method. However, if oxidized at relatively low
Specification B 476 is applicable to strip, rod, or wire only. Test Method
pressures, a binary silver-tin alloy develops a stable layer of tin
C 914 is applicable to forms less than 99 % dense.
oxide at the surface which inhibits further oxidation of the
material. Because of this phenomenon, usually at least a third
3. Terminology
element (such as indium) is added to the alloy in order to
3.1 Definitions of Terms Specific to This Standard:
promote internal oxidation. Oxidation may be carried out under
3.1.1 lot—(usage involving discrete manufactured parts)—
elevated oxygen pressure and also at various temperatures;
all parts of the same form, and dimensions, from the same alloy
oxidation conditions determine size and distribution of the
melt or batch of particulate (if manufactured by consolidation),
resulting oxide particles. Other manufacturing processes utilize
powder metallurgical techniques. Silver- and tin-oxide pow-
ders may be blended and consolidated by heat or pressure, or
This guide is under the jurisdiction of ASTM Committee B-2 on Nonferrous
both, into wire or strip suitable for further processing, or may
Metals and Alloys and is the direct responsibility of Subcommittee B2.05 on
be blended and sintered directly into contacts. Methods that
Precious Metals.
Current edition approved May 10, 1998. Published October 1998. Originally
can be used to prepare silver- and tinoxide powder mixtures
published as B 844–93. Last previous edition B 844–93.
include either coprecipitation or sequential precipitation of
Annual Book of ASTM Standards, Vol 02.05.
3 silver and tin compounds from aqueous solutions, coating of
Annual Book of ASTM Standards, Vol 03.04.
Annual Book of ASTM Standards, Vol 15.01. tin-oxide particles by precipitation of silver from an aqueous
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B 844
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
these materials due to both compositional and processing
specific manufacturing period. differences, no substitutio
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