ASTM_B_457_-_67_2013.pdf

Designation:B45767(Reapproved 2013)Standard Test Method forMeasurement of Impedance of Anodic Coatings onAluminum1This standard is issued under the fixed designation B457;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 describes the conditions and equipmentfor measuring the impedance of anodic coatings on aluminum.Such measurements have been used to evaluate the quality ofseal of an anodic coating.The test method does not prescribethe procedure for producing the anodic coating,nor thepostanodizing treatment usually described as“sealing.”1.2 This test method is applicable to the rapid,nondestruc-tive testing of anodic coatings.The interpretation of results andcorrelation of data with service experience and other tests arenot within the scope of this test method.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.4 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.Nature of Test2.1 Impedance is an electrical characteristic described as thetotal opposition of all circuit elements to the flow of alternatingcurrent.Inductive effects of anodic coatings are negligible andthe impedance is presumed to be made up of resistance andcapacitive reactance according to the following relationships:Z 5=R21Xc2(1)andXc5 1/2 f C(2)where:Z=impedance,R=resistance,Xc=capacitive reactance,f=frequency,andC=capacitance.2.2 Both resistance and capacitance are associated with amaterial constant and a geometric factor:R 2 rl/A!(3)where:R=resistance,r=specific resistance,l=length of conductor,andA=area of cross section of conductor.C 5 eA/l!(4)where:C=capacitance,e=dielectric constant,A=area of opposing plates of capacitor,andl=distance between plates.2.3 For measuring impedance of anodic coatings,the mate-rial constants are partly associated with the anodic coating andpartly with the electrolyte employed in the test cell.Forsimplification these constants are assumed not to vary.Thevariations in measured impedance then depend directly ongeometric factors.23.Apparatus3.1 Impedance BridgesCommercially available a-c im-pedance bridges with the following characteristics are satisfac-tory:33.1.1 Range1 F(1000 nF)to 0.0001 F(0.1 nF)fullscale with a dissipation factor of 0 to 2.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 onConversion Coatings.Current edition approved May 1,2013.Published May 2013.Originallyapproved in 1967.Last previous edition approved in 2008 as B457 67(2008)1.DOI:10.1520/B0457-67R13.2The Alcoa Impedance Test for Anodic Coatings(AZTAC)evaluates a 0.129-cm2(0.02-in.2)test area and expresses impedance in kilohms.Instructions areavailable fromAlcoa Process Development Laboratories,P.O.Box 2970,Pittsburgh,PA 15230.3The Z-Scope,formerly manufactured by Twin City Testing Corp.,Tonawanda,NY was designed to measure the impedance of anodic coatings on aluminum.AZTAC values(the impedance of a 0.129-cm2(0.02-in.2)test area)can be readdirectly in kilohms with this instrument.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.2 Frequency1000 Hz.3.1.3 Accuracy1%.3.1.4 VoltageAdjustable so as to be not greater than 0.5 Vas applied to the test specimen.3.2 Cell(Fig.1)for containing the electrolyte during test.Itmay be constructed from the following components:43.2.1 Glass Tube,9 mm(0.35 in.)in outside diameter by 9cm(3.54 in.).3.2.2 Rubber Gasket or Seal.53.2.3 Rubber StopperAny convenient size with a hole incenter to accommodate the glass tube.3.2.4 Platinum or Type 300 Stainless Steel CounterElectrode,9 cm(3.54 in.)long by 0.75 to 1.0 mm(0.030 to0.040 in.)diameter wire.3.3 Wire Leads,two,insulated,approximately 1 m(40 in.)long complete with C-clamps or alligator clips shall be used formaking connections to the test specimen and cell electrode.3.4 Support Strand,complete with a utility clamp to holdthe electrolytic test cell.3.5 Glass or Stainless Steel Tank containing pure boilingwater is required for conditioning the test specimen.3.6 Container for Cell StandardizationA 150 to 500-mLType 300 stainless steel beaker or standard 1-in.2test cell6maybe used.4.Electrolyte4.1 The electrolyte shall be a 312%solution of sodiumchloride prepared by dissolving 36 g of the salt in 1 L ofdistilled or deionized water.5.Test Specimen5.1 The area to be tested should be sufficiently large toaccommodate the test cell,suf