Designation:D2674−72(Reapproved2012)StandardMethodsofAnalysisofSulfochromateEtchSolutionUsedinSurfacePreparationofAluminum1ThisstandardisissuedunderthefixeddesignationD2674;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thesemethodsofferameansforcontrollingtheeffec-tivenessoftheetchantwhichisnormallyusedforpreparingthesurfaceofaluminumalloysforsubsequentadhesivebonding.Astheetchantreactswiththealuminum,hexavalentchromiumisconvertedtotrivalentchromium;ameasureofthetwoandthedifferencecanbeusedtodeterminetheamountofdichro-mateused.1.2Thesulfochromatesolutioncanbereplenishedbyre-storingthesodiumdichromateandthesulfuricacidtotheoriginalformulationlevels.Thelowerlimitofusefulnesswillvarydependinguponsolutionstorage,adhesivesused,criticalnatureofbondcapability,varietyofmetalsprocessed,etc.andshouldbedetermined.Replenishmentwillbelimitedtothenumberoftimesthechemicalingredientscanberestoredandmaintainedtotherequiredlevelsandshouldbedeterminedbytheuser.Sludgecollectinginthebottomofatankshouldbeminimizedbyperiodicremovalofsludge.Forsomeapplica-tions,thehexavalentchromiumshouldnotfallbelowthetrivalentchromiumcontent.1.3Atypicalaqueoussulfochromateacidetchsolutionformulationisasfollows:Sodiumdichromate(Na2Cr2O7)4.5oz/gal(33.7g/litre)Sulfuricacid(spgr1.84)45oz/gal(337.1g/litre)1.4Maintenanceoftheaqueousconcentrationsissuggestedasfollowsbyappropriateadditionsofsodiumdichromateorsulfuricacids.Sodiumdichromate3.0to6.0oz/gal(22.5to44.9g/litre)Sulfuricacid40to50oz/gal(299.6to374.5g/litre)1.5MethodAisintendedformeasuringthesulfuricacidcontentofasulfochromatesolution.MethodBisintendedformeasuringthehexavalentandtrivalentChromiumcontentofasulfochromatesolution.MethodCisintendedasanalternativemethodformeasuringthehexavalentandtrivalentChromiumcontentofasulfochromatesol...
