ASTM_D_6845_-_20.pdf

Designation:D684520Standard Test Method forSilica,Precipitated,HydratedCTAB(Cetyltrimethylammonium Bromide)Surface Area1This standard is issued under the fixed designation D6845;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 covers the measurement of the specificsurface area of precipitated silicas exclusive of area containedin micropores too small to admit hexadecyltrimethylammo-nium bromide(cetyltrimethylammonium bromide,commonlyreferred to as CTAB)molecules.This test method is suitablefor characterizing rubber-grade silicas of all types.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1799 Practice for Carbon BlackSampling PackagedShipmentsD1900 Practice for Carbon BlackSampling Bulk Ship-mentsD4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3.Summary of Test Method3.1 The isotherm for adsorption of an aqueous solution ofCTAB on silicas has a long horizontal plateau corresponding toa monolayer coverage of the substrate surface from which theadsorbate is not sterically excluded.The CTAB adsorption bysilica is independent of functional groups containing hydrogenand oxygen,etc.Rapid equilibration is achieved by usingmechanical stirring.Titration with dioctyl sodium sulfosucci-nate(Aerosol OT3)solution to a turbidity maximum end pointis used to determine the unadsorbed CTAB after removal of thecolloidally dispersed silica by ultrafiltration.3.2 Titration of the unadsorbed CTAB with Aerosol OTsolution is accomplished by automatic titration.4.Significance and Use4.1 The CTAB molecule is relatively large;so it is notadsorbed in micropores or on surface roughness.Thus,theCTAB surface area reflects only the surface of the silica that isavailable for interaction with rubber molecules.5.Apparatus5.1 Analytical Balance,0.1 mg sensitivity.5.2 Centifuge,capable of 67 rev/s(4000 r/m).5.3 Magnetic Spinbars,4chemically resistant covered(poly-chlorotrifluoroethylene or TFE-fluorocarbon),6.4-or 4.8-mm(14-or316-in.)diameter,and length nearly equal to thediameter of 50 or 100 cm3Berzelius beakers,glass vials,orother glass vessels.5.4 Glass Funnel,small.5.5 Glass Vials,with plastic screw caps,28 mm in outsidediameter,about 40 cm3capacity.5.6 Buret,50 cm3,0.1 cm3divisions,Class A,preferably ofautomatic refilling and zeroing type(see Note 1)with reagentreservoir.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand Rubber-like Materials and is the direct responsibility of Subcommittee D11.20on Compounding Materials and Procedures.Current edition approved June 1,2020.Published June 2020.Originallyapproved in 2002.Last previous edition approved in 2018 as D6845 18.DOI:10.1520/D6845-20.2For 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.3Aerosol OT is a registered trademark of the American Cyanamid Co.,ProcessChemicals Dept.,Wayne,NM 07470.4Examples of suitable spinbars are Catalog No.9235-U7,A.H.Thomas Co.,Philadelphia,PA 19105,or Catalog No.S-76497-30,Sargent Welch Scientific Co.,Skokie,IL 60076.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.NOTE1Automatic burets are usually not certified to Class A toler-ance.Such burets should be checked for accuracy,and if in error by morethan 0.05 cm3at any point,a calibration curve should be prepared andused to correct observed buret readings.Burets with TFE-fluorocarbonmanostat valves offer some advantage in ease of stopcock