ASTM_B_825_-_13.pdf

Designation:B82513Standard Test Method forCoulometric Reduction of Surface Films on Metallic TestSamples1This standard is issued under the fixed designation B825;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 method covers procedures and equipment fordetermining the relative buildup of corrosion and tarnish films(including oxides)on metal surfaces by the constant-currentcoulometric technique,also known as the cathodic reductionmethod.1.2 This test method is designed primarily to determine therelative quantities of tarnish films on control coupons thatresult from gaseous environmental tests,particularly when thelatter are used for testing components or systems containingelectrical contacts used in customer product environments.1.3 This test method may also be used to evaluate testsamples that have been exposed to indoor industrial locationsor other specific application environments.(See 4.6 for limi-tations.)1.4 This test method has been demonstrated to be applicableparticularly to copper and silver test samples(see(1).2Othermetals require further study to prove their applicability withinthe scope of this test method.1.5 The values stated in SI units are the preferred units.Thevalues provided in parentheses are for information only.1.6 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 appropriateMaterial Safety Data Sheet(MSDS)for this product/materialas provided by the manufacturer,to establish appropriatesafety and health practices,and determine the applicability ofregulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:3B808 Test Method for Monitoring ofAtmospheric CorrosionChambers by Quartz Crystal MicrobalancesB809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor(“Flowers-of-Sulfur”)B810 Test Method for Calibration ofAtmospheric CorrosionTest Chambers by Change in Mass of Copper CouponsB827 Practice for Conducting Mixed Flowing Gas(MFG)Environmental TestsD1193 Specification for Reagent Water3.Summary of Test Method3.1 In constant-current coulometry,a fixed reduction-current density is applied to the sample in an electrolyticallyconductive solution,and the resulting variations in potentialmeasured against a standard reference electrode in the samesolutionare followed as a function of time.Typically,withwell-behaved surface films,the voltage-time plot should showa number of horizontal portions,or steps,each correspondingto a specific reduction potential or voltage(Fig.1).The finalpotential step,which is always present with all substances,corresponds to the reduction of hydrogen ions in the solution(to form hydrogen gas),and represents a limit beyond which nohigher potential reduction process can occur.NOTE1As shown in Figs.1 and 2,a differential circuit is recom-mended to help in resolving the individual voltage steps by pinpointing thecorresponding inflection points on the main reduction curve(see 6.2.3).3.2 From the elapsed times at the various steps,conclusionscan often be drawn regarding the corrosion processes that havetaken place to produce the surface films.Also,calculations canbe made from the time at each voltage step in order to calculatethe number of coulombs of electrical charge required tocomplete the reduction process at that particular voltage.1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved Aug.1,2013.Published August 2013.Originallyapproved in 1997.Last previous edition approved in 2008 as B825 02(2008).DOI:10.1520/B0825-13.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For 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 International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Furthermore,since the reduction of any particular chemicalcompound takes place at a characteristic reduction potential orvoltage range,this voltage can be used to indicate the presenceof a compound or compounds whose characteristic reductionpotential has already been established under the conditions ofthe test.Under ideal conditions it may also be possible todetermine the number of reducible compounds present in thetarnish film.3.3 For the purpose of this test method,tarnish films shall bedefined as the corro