ASTM B844-98(2021)

Standard Guide for Silver-Tin Oxide Contact Material

SIGNIFICANCE AND USE
4.1 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’s 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 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 Safety Data Sheet (SDS) for this product/material as provided by the manufacturer, to establish appropriate safety, health, and environmental practices, and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2021
• ICS: 77.120.99 - Other non-ferrous metals and their alloys
• Technical Committee: B02 - Nonferrous Metals and Alloys
• Drafting Committee: B02.05 - Precious Metals and Electrical Contact Materials and Test Methods

Relations

• Refers: ASTM B311-13 - Standard Test Method for Density of Powder Metallurgy (PM) Materials Containing Less Than Two Percent Porosity
• Effective Date: 01-Apr-2013
• Refers: ASTM B476-01(2012) - Standard Specification for General Requirements for Wrought Precious Metal Electrical Contact Materials
• Effective Date: 01-May-2012
• Refers: ASTM B311-08 - Standard Test Method for Density of Powder Metallurgy (PM) Materials Containing Less Than Two Percent Porosity
• Effective Date: 01-Dec-2008
• Refers: ASTM B476-01(2006) - Standard Specification for General Requirements for Wrought Precious Metal Electrical Contact Materials
• Effective Date: 01-Jun-2006
• Refers: ASTM B476-01 - Standard Specification for General Requirements for Wrought Precious Metal Electrical Contact Materials
• Effective Date: 10-May-2001
• Refers: ASTM B311-93(2002)e1 - Test Method for Density Determination for Powder Metallurgy (P/M) Materials Containing Less Than Two Percent Porosity
• Effective Date: 15-Dec-1993

Overview

ASTM B844-98(2021): Standard Guide for Silver-Tin Oxide Contact Material provides essential guidelines for manufacturers and users of silver-tin oxide materials employed in electrical contact applications. Developed by ASTM International, this standard addresses the specific requirements and considerations for silver-tin oxide materials, which are vital in producing reliable and efficient electrical contacts. These contact materials are widely used in forms such as strip, rod, wire, and discrete parts, contributing to the performance of various electrical devices and systems.

Key Topics

• Material Definitions and Scope

  • Covers silver-tin oxide materials containing silver, tin oxide, and other metal oxides.
  • Applies to various forms including strips, rods, wires, and finished contact parts.
  • Highlights that manufacturing processes can be proprietary and vary between suppliers.

• Manufacturing Methods

  • Notes significant differences in manufacturing methods, such as internal oxidation and powder metallurgy.
  • Influences on performance characteristics include arc erosion resistance, contact resistance, and welding tendency.

• Chemical Composition

  • Focuses on the agreement between producer and user regarding material composition, additives, and impurities.
  • Emphasizes careful control of additives due to their effect on material performance.

• Performance and Qualification

  • States that contact performance is influenced by factors beyond the material itself (e.g., device operation, environmental conditions).
  • Recommends electrical testing under real device conditions for qualification.
  • Stresses the need for agreement on acceptable properties and microstructure between manufacturers and users.

• Sampling and Inspection

  • Details requirements for inspection of batches (lots) and the importance of conformity to agreed quality measures.

• Change Control

  • Requires notification and approval for substantive changes in composition or manufacturing methods.

Applications

Silver-tin oxide contact materials are crucial in:

• Electrical Switching Devices

  • Circuit breakers, relays, and contactors utilize silver-tin oxide contacts for their arc erosion and welding resistance.

• Industrial and Consumer Electronics

  • Employed in switches and connectors where reliable current interruption and minimal contact resistance are mandatory.

• Custom Electrical Assemblies

  • Utilized for bespoke or high-reliability components where user and manufacturer can specify material properties for optimal performance.

Key Benefits:

• Provides a framework for agreement between supplier and buyer, ensuring materials meet application-specific needs.
• Encourages the use of established test methods and qualification protocols to maintain quality and consistency.
• Supports ongoing quality management by requiring clarity on changes and allowing for specific contract requirements.

Related Standards

This standard references and aligns with other important ASTM documents, including:

• ASTM B311: Test Method for Density of Powder Metallurgy Materials

  • Used for evaluating the density of silver-tin oxide in certain forms.

• ASTM B476: Specification for Wrought Precious Metal Electrical Contact Materials

  • Applies to wires, rods, and strips, offering general requirements for these forms of contact materials.

• International Alignment:

  • Developed with the World Trade Organization's principles for standardization in mind, ensuring broad international relevance and acceptance.

Conclusion

ASTM B844-98(2021) is an essential resource for anyone involved in the manufacture, procurement, or application of silver-tin oxide electrical contact materials. By defining best practices for material specification, testing, and quality assurance, it helps ensure high-performance, safety, and consistency in critical electrical applications. For optimal results, both manufacturers and users should reference this guide when selecting or qualifying silver-tin oxide contact materials for their electrical devices.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B844 − 98 (Reapproved 2021)
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 3.1.1 lot, n—(usage involving discrete manufactured
parts)—all parts of the same form, and dimensions, from the
1.1 This standard provides guidelines for users and manu-
same alloy melt or batch of particulate (if manufactured by
facturers of silver-tin oxide material produced in strip, rod,
consolidation), processed under the same conditions, and
wire, and part form for electrical contact applications.
submitted for inspection at the same time.
1.2 Silver-tin oxide refers to contact material containing
silver, tin oxide, and other metal oxide which may be used for
4. Significance and Use
eitherimprovingtheprocessingorperformanceofthematerial.
4.1 The methods for manufacture (proprietary or otherwise)
1.3 This standard does not purport to address all of the
ofthesematerialsvarysignificantlyamongsuppliers,andthese
safety concerns, if any, associated with its use. It is the
methods influence such properties as arc erosion, contact
responsibility of the user of this standard to become familiar
resistance, and tendency to weld in service. Since the perfor-
with all hazards including those identified in the appropriate
mance of contacts in a device depends on numerous factors
Safety Data Sheet (SDS) for this product/material as provided
outsidethecontactitself(openingspeed,closingspeed,contact
by the manufacturer, to establish appropriate safety, health,
pressure, contact bounce, environmental variations, assembly
and environmental practices, and determine the applicability
technique and variations, etc.) this guide cannot ensure perfor-
of regulatory limitations prior to use.
mance control in the application.As part of the qualification on
1.4 This international standard was developed in accor-
initial samples it is recommended that the user electrically test
dance with internationally recognized principles on standard-
the materials in a functional manner for all devices applicable
ization established in the Decision on Principles for the
to the material’s use. This guide will provide a means for the
Development of International Standards, Guides and Recom-
contact manufacturer and contact user to reach agreement on
mendations issued by the World Trade Organization Technical
the details of material to be supplied for a specific use and how
Barriers to Trade (TBT) Committee.
to provide reasonable assurance that future lots will be similar
in properties and microstructure to the initial test of sample
2. Referenced Documents
contacts supplied.
2.1 ASTM Standards:
B311 Test Method for Density of Powder Metallurgy (PM) 5. Materials and Manufacture
Materials Containing Less Than Two Percent Porosity
5.1 Various processes may be utilized to produce silver-tin
B476 Specification for General Requirements for Wrought
oxide contact materials. Internal oxidation of a silver-tin alloy
Precious Metal Electrical Contact Materials
is a viable method. However, if oxidized at relatively low
pressures, a binary silver-tin alloy develops a stable layer of tin
NOTE 1—Test Method B311 is applicable to fully dense forms.
Specification B476 is applicable to strip, rod, or wire only. Test Method is
oxide at the surface which inhibits further oxidation of the
applicable to forms less than 99 % dense.
material. Because of this phenomenon, usually at least a third
element (such as indium) is added to the alloy in order to
3. Terminology
promoteinternaloxidation.Oxidationmaybecarriedoutunder
3.1 Definitions of Terms Specific to This Standard:
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 Nov. 1, 2021. Published December 2021. Originally
both, into wire or strip suitable for further processing, or may
approved in 1993. Last previous edition approved in 2016 as B844 – 98 (2016).
DOI: 10.1520/B0844-98R21.
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 tin-oxide powder mixtures
contact ASTM Customer Service at [e-mail]. 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
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B844 − 98 (2021)
tin-oxide particles by precipitation of silver from an aqueous amount by the producer. Additionally, various impurities may
solution, and powder atomization of a silver-base alloy fol- remain in these materials from raw materials or processing
lowed by internal oxidation of the atomized powder. which have been found to be either detrimental or helpful
5.1.1 Silver-tin oxide materials are used in various tempers depending on the residual level and the individual application.
dependent on the attachment and fabrication process utilized. Chemical requirements for such elements and analytical meth-
5.1.2 For purposes of attachment or device performance, ods to be employed shall be mutually agreed upon between the
silver-tin oxide contact material is often produced with a producer and the user.
conductive or brazable layer of material or backing. Incorpo- 6.2.2 It should be noted that the operating characteristics of
ration of such a layer is often an integral part of the silver-tin
silver-tin oxide materials with different additives may be very
oxide manufacturing process. different. Certain operating characteristics such as welding
5.1.3 Silver-tin ox
...