ASTM_B_844_-_98_2016.pdf

Designation:B84498(Reapproved 2016)Standard Guide forSilver-Tin Oxide Contact Material1This standard is issued under the fixed designation B844;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This standard provides guidelines for users and manu-facturers 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 containingsilver,tin oxide,and other metal oxide which may be used foreither improving the processing or performance of the material.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateSafety Data Sheet(SDS)for this product/material as providedby the manufacturer,to establish appropriate safety and healthpractices,and determine the applicability of regulatory limi-tations prior to use.2.Referenced Documents2.1 ASTM Standards:2B311 Test Method for Density of Powder Metallurgy(PM)Materials Containing Less Than Two Percent PorosityB476 Specification for General Requirements for WroughtPrecious Metal Electrical Contact MaterialsNOTE1Test Method B311 is applicable to fully dense forms.Specification B476 is applicable to strip,rod,or wire only.Test Method isapplicable to forms less than 99%dense.3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 lot,n(usage involving discrete manufacturedparts)all parts of the same form,and dimensions,from thesame alloy melt or batch of particulate(if manufactured byconsolidation),processed under the same conditions,andsubmitted for inspection at the same time.4.Significance and Use4.1 The methods for manufacture(proprietary or otherwise)of these materials vary significantly among suppliers,and thesemethods influence such properties as arc erosion,contactresistance,and tendency to weld in service.Since the perfor-mance of contacts in a device depends on numerous factorsoutside the contact itself(opening speed,closing speed,contactpressure,contact bounce,environmental variations,assemblytechnique and variations,etc.)this guide cannot ensure perfor-mance control in the application.As part of the qualification oninitial samples it is recommended that the user electrically testthe materials in a functional manner for all devices applicableto the materials use.This guide will provide a means for thecontact manufacturer and contact user to reach agreement onthe details of material to be supplied for a specific use and howto provide reasonable assurance that future lots will be similarin properties and microstructure to the initial test of samplecontacts supplied.5.Materials and Manufacture5.1 Various processes may be utilized to produce silver-tinoxide contact materials.Internal oxidation of a silver-tin alloyis a viable method.However,if oxidized at relatively lowpressures,a binary silver-tin alloy develops a stable layer of tinoxide at the surface which inhibits further oxidation of thematerial.Because of this phenomenon,usually at least a thirdelement(such as indium)is added to the alloy in order topromote internal oxidation.Oxidation may be carried out underelevated oxygen pressure and also at various temperatures;oxidation conditions determine size and distribution of theresulting oxide particles.Other manufacturing processes utilizepowder metallurgical techniques.Silver-and tin-oxide pow-ders may be blended and consolidated by heat or pressure,orboth,into wire or strip suitable for further processing,or maybe blended and sintered directly into contacts.Methods thatcan be used to prepare silver-and tinoxide powder mixturesinclude either coprecipitation or sequential precipitation ofsilver and tin compounds from aqueous solutions,coating oftin-oxide particles by precipitation of silver from an aqueoussolution,and powder atomization of a silver-base alloy fol-lowed by internal oxidation of the atomized powder.5.1.1 Silver-tin oxide materials are used in various tempersdependent on the attachment and fabrication process utilized.1This guide is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.05 onPrecious Metals and Electrical Contact Materials.Current edition approved May 1,2016.Published May 2016.Originallyapproved in 1993.Last previous edition approved in 2010 as B844 98(2010).DOI:10.1520/B0844-98R16.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM Intern