Designation:D6845−20StandardTestMethodforSilica,Precipitated,Hydrated—CTAB(CetyltrimethylammoniumBromide)SurfaceArea1ThisstandardisissuedunderthefixeddesignationD6845;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthemeasurementofthespecificsurfaceareaofprecipitatedsilicasexclusiveofareacontainedinmicroporestoosmalltoadmithexadecyltrimethylammo-niumbromide(cetyltrimethylammoniumbromide,commonlyreferredtoasCTAB)molecules.Thistestmethodissuitableforcharacterizingrubber-gradesilicasofalltypes.1.2ThevaluesstatedinSIunitsaretoberegardedasthestandard.Thevaluesgiveninparenthesesareforinformationonly.1.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafety,health,andenvironmentalpracticesanddeter-minetheapplicabilityofregulatorylimitationspriortouse.1.4Thisinternationalstandardwasdevelopedinaccor-dancewithinternationallyrecognizedprinciplesonstandard-izationestablishedintheDecisiononPrinciplesfortheDevelopmentofInternationalStandards,GuidesandRecom-mendationsissuedbytheWorldTradeOrganizationTechnicalBarrierstoTrade(TBT)Committee.2.ReferencedDocuments2.1ASTMStandards:2D1193SpecificationforReagentWaterD1799PracticeforCarbonBlack—SamplingPackagedShipmentsD1900PracticeforCarbonBlack—SamplingBulkShip-mentsD4483PracticeforEvaluatingPrecisionforTestMethodStandardsintheRubberandCarbonBlackManufacturingIndustries3.SummaryofTestMethod3.1TheisothermforadsorptionofanaqueoussolutionofCTABonsilicashasalonghorizontalplateaucorrespondingtoamonolayercoverageofthesubstratesurfacefromwhichtheadsorbateisnotstericallyexcluded.TheCTABadsorptionbysilicaisindependentoffunctionalgroupscontaininghydrogenandoxygen,etc.Rapidequilibrationisachievedbyusingme...
