Designation:B556−90(Reapproved2013)StandardGuideforMeasurementofThinChromiumCoatingsbySpotTest1ThisstandardisissuedunderthefixeddesignationB556;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thisguidecoverstheuseofthespottestforthemeasurementofthicknessesofelectrodepositedchromiumcoatingsovernickelandstainlesssteelwithanaccuracyofabout620%(Section9).Itisapplicabletothicknessesupto1.2µm.2NOTE1—Althoughthistestcanbeusedforcoatingthicknessesupto1.2µm,thereisevidencethattheresultsobtainedbythismethodarehighatthicknessesgreaterthan0.5µm.3Inaddition,forcoatingthicknessesabove0.5µm,itisadvisabletouseadoubledropofacidtopreventdepletionofthetestsolutionbeforecompletionofthetest.1.2Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.ReferencedDocuments2.1ASTMStandards:4B504TestMethodforMeasurementofThicknessofMetal-licCoatingsbytheCoulometricMethodB568TestMethodforMeasurementofCoatingThicknessbyX-RaySpectrometryB588TestMethodforMeasurementofThicknessofTrans-parentorOpaqueCoatingsbyDouble-BeamInterferenceMicroscopeTechnique3.SummaryofGuide3.1Adropofhydrochloricacid(testsolution)isdepositedonthesurfaceofthetestspecimen,andthetimerequiredforthehydrochloricacidtopenetratethroughthechromiumcoating(penetrationtime)ismeasured.Thecoatingthicknessisproportionaltothistime.4.SignificanceandUse4.1Thethicknessofadecorativechromiumcoatingisoftencriticaltoitsperformance.4.2Thisprocedureisusefulforanapproximatedetermina-tionwhenthebestpossibleaccuracyisnotrequired.Formorereliabledeterminations,thefollowingmethodsareavailable:MethodsB504,B568,andB588.4.3Thistestassumesthattherateofd...
