ASTM_B_764_-_04_2014.pdf

Designation:B76404(Reapproved 2014)Standard Test Method forSimultaneous Thickness and Electrode PotentialDetermination of Individual Layers in Multilayer NickelDeposit(STEP Test)1This standard is issued under the fixed designation B764;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 closely estimates the thickness ofindividual layers of a multilayer nickel electrodeposit and thepotential differences between the individual layers while beinganodically stripped at constant current density.2,31.2 This test method does not cover deposit systems otherthan multilayer electroplated nickel deposits.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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:4B456 Specification for Electrodeposited Coatings of CopperPlus Nickel Plus Chromium and Nickel Plus ChromiumB504 Test Method for Measurement of Thickness of Metal-lic Coatings by the Coulometric MethodD1193 Specification for Reagent Water3.Summary of Test Method3.1 This procedure is a modification of the well-knowncoulometric method of thickness testing(Test Method B504).It is also known as the anodic dissolution or electrochemicalstripping method.3.2 Coulometric thickness testing instruments are based onthe anodic dissolution(stripping)of the deposit at constantcurrent,while the time is measured to determine thickness.Ascommonly practiced,the method employs a small cell that isfilled with an appropriate electrolyte,and the test specimenserves as the bottom of the cell.To the bottom of the cell isattached a rubber or plastic gasket whose opening defines themeasuring(stripping,anodic)area.If a metallic cell is used,therubber gasket also electrically insulates the test specimen fromthe cell.With the specimen as the anode and the cell or agitatortube as the cathode,a constant direct current is passed throughthe cell until the nickel layer is dissolved.A sudden change involtage between the electrodes occurs when a different metalliclayer starts to dissolve.3.3 Each different metal or species of the same metalrequires a given voltage to keep the current constant whilebeing stripped.As one nickel layer is dissolved away and thenext layer becomes exposed,there will be a voltage change(assuming a constant current and difference in the electro-chemical characteristics of the two nickel layers).The elapsedtime at which this voltage change occurs(relative to the start ofthe test or previous voltage change)is a measure of the depositthickness.3.4 At the same time,the amplitude of the voltage changecan be observed.That is,the ease(or difficulty)with which onelayer can be dissolved or stripped with reference to anotherlayer can be compared.The lower the voltage needed the moreactive the metal or the greater the tendency to corrodepreferentially to a more noble metal adjacent to it.3.5 Where the metallic layers are of such a similar naturethat change of the stripping voltage is small,there can beproblems in detecting this change if the voltage between thedeplating cell(cathode)and the sample(anode)is measured.As the sample is dissolved anodically,cathodic processes areoccurring on the deplating cell(cathode)surface that can alsogive rise to voltage changes,due to alterations of the cathodesurface,thus obscuring the anode voltage change.This diffi-culty can be avoided by measuring the potential of thedissolving anodic sample with respect to an unpolarized thirdelectrode(reference)placed in the cell.By recording this1This method is under the jurisdiction ofASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1986.Last previous edition approved in 2009 as B764 04(2009).DOI:10.1520/B0764-04R14.2For discussion of this test,see Harbulak,E.P.,“Simultaneous Thickness andElectrochemical Potential Determination of Individual Layers in Multilayer NickelDeposits,”Plating and Surface Finishing,Vol 67,No.2,February 1980,pp.4954.3U.S.Patent 4,310,389.Assignee:The Chrysler Corp.,Highland Park,MI48203.4For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 potential any difference in electrochemical activity betweenlayers is more readily d