ASTM_B_920_-_16.pdf

Designation:B92016Standard Practice forPorosity in Gold and Palladium Alloy Coatings on MetalSubstrates by Vapors of Sodium Hypochlorite Solution1This standard is issued under the fixed designation B920;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 test practice covers equipment and methods forrevealing the porosity of gold and palladium coatings,particu-larly electrodeposits and clad metals used on electrical con-tacts.1.2 This test practice is suitable for coatings containing goldor 75%by mass of palladium on substrates of copper,nickel,and their alloys,which are commonly used in electricalcontacts.1.3 Avariety of full porosity testing methods is described inthe literature.2,3These porosity Test Methods are B735,B741,B798,B799,and B809.An ASTM Guide to the selection ofporosity tests for electrodeposits and related metallic coatingsis available as Guide B765.1.4 The values stated in SI units are to be regarded asstandard.The values given in parentheses are for informationonly.1.5 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For specifichazards,see Section 6.2.Referenced Documents2.1 ASTM Standards:4B374 Terminology Relating to ElectroplatingB542 Terminology Relating to Electrical Contacts and TheirUseB735 Test Method for Porosity in Gold Coatings on MetalSubstrates by Nitric Acid VaporB741 Test Method for Porosity In Gold Coatings On MetalSubstrates By Paper Electrography(Withdrawn 2005)5B765 Guide for Selection of Porosity and Gross Defect Testsfor Electrodeposits and Related Metallic CoatingsB798 Test Method for Porosity in Gold or Palladium Coat-ings on Metal Substrates by Gel-Bulk ElectrographyB799 Test Method for Porosity in Gold and PalladiumCoatings by Sulfurous Acid/Sulfur-Dioxide VaporB809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor(“Flowers-of-Sulfur”)3.Terminology3.1 DefinitionsMany terms used in this practice are de-fined in Terminology B542 and terms relating to metalliccoatings are defined in Terminology B374.3.2 Definitions of Terms Specific to This Standard:3.2.1 corrosion products,nthose reaction products ema-nating from the pores that protrude from,or are otherwiseattached to,the coating surface after a vapor test exposure.3.2.2 metallic coatings,ninclude platings,claddings,orother metallic layers applied to the substrate.The coatings cancomprise a single metallic layer or a combination of metalliclayers.3.2.3 porosity,nthe presence of any discontinuity,crack,or hole in the coating that exposes a different underlying metal.3.2.4 underplate,na metallic coating layer between thesubstrate and the topmost layer or layers.The thickness of anunderplate is usually greater than 0.8 m(30 in.).4.Summary of Practice4.1 The test practice employs a solution of sodiumhypochlorite,a material readily available as household bleach.The test is recommended primarily as a qualitative means forassessing the plating quality in electrical connectors and isdesirable because it uses readily available reagents and equip-ment and is extremely inexpensive,simple,and fast.In the test,1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Oct.1,2016.Published October 2016.Originallyapproved in 2001.Last previous edition approved in 2011 as B920 01(2011).DOI:10.1520/B0920-16.2For example see:Nobel,F.J.,Ostrow,B.D.,and Thompson,D.W.,“PorosityTesting of Gold Deposits,”Plating,Vol 52,1965,p.1001.3Krumbien,S J.,Porosity Testing of Contact Platings,Proceedings,Connectorsand Interconnection Technology Symposium,Oct.1987,p.47.4For 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.5The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 the coated parts to be evaluated are suspended above a solutionof sodium hypochorite in a vessel that is closed but not sealed.Paper towels extend from the solution in the bottom part of theway up the sides of vessel providing a wicking action for thesolution.After exposure in this manner for 30 to 45 min,theparts are removed from the vessel,dried with hot air andexamined for the presence of corrosion products that indicatep