1、Designation:D801622Standard Test Method forSilica,Precipitated,HydratedSears Number1This standard is issued under the fixed designation D8016;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 paren
2、theses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method is used to determine the number ofsilanol groups on the surface of silica by titration according toa method as developed by Sears.This te
3、st method is suitablefor characterizing rubber-grade silicas.1.2 UnitsThe values stated in SI units are to be regardedas the standard.No other units of measurement are included inthis standard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It i
4、s 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 stan
5、dard-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:2D4483 Practice for Evaluating Precision for Test
6、MethodStandards in the Rubber and Carbon Black ManufacturingIndustriesD6738 Test Method for Precipitated SilicaVolatile Con-tent3.Summary of Test Method3.1 An ion exchange reaction in silica is possible based onthe acidic character of the surface silanol groups.According toSears,3it is possible to d
7、etermine the surface area of colloidalsilica on the basis of this ion exchange mechanism,aftercertain preliminary treatments,by titration with a basic solu-tion.The initial preliminary treatment step consists of exposureof the silica to a sufficiently concentrated solution of sodiumchloride(NaCl).Af
8、ter this the suspension of silica and NaCl isback-titrated with sodium hydroxide solution.3.2 A 1.5 g sample of silica is weighed into a 250 cm3beaker containing 150 cm3NaCl solution adjusted to pH 3.Thesuspension is stirred for 3 min and brought to 25C.Thesuspension is titrated first to pH 4 and th
9、en to pH 9 using asodium hydroxide solution(c=0.1 mol/dm3).The volume ofsodium hydroxide solution that is reacted between pH 4 and pH9 is calculated and corrected with the volatile matter deter-mined according to Test Method D6738.The consumption ofsodium hydroxide solution minus the blank reading w
10、ithoutsilica is defined as the Sears Number given in cm3/1.5 g.Thespecific consumption of sodium hydroxide solution in a silicasuspension depends primarily on the silica surface area,thedensity of the silanol groups,and the degree of hydrophobicity.4.Significance and Use4.1 The rubber-filler interac
11、tion needed in silica technologyfor the rubber industry is based on the use of silane-couplingagents that react with the silanol groups on the surface of thesilica during the processing step called silanization.Silane-coupling agents are multifunctional molecules able to createmolecular bridges betw
12、een the elastomer or rubber matrix andthe silica surface.5.Apparatus5.1 Precision Balance,0.01 g sensitivity.5.2 Automatic Titration Apparatus,capable of performing avolumetric endpoint titration based on pH,as well as equippedwith data storage and calculation modules.4Use of an auto-matic titrator
13、for this method is recommended.However,manual titration may be performed provided that the titrationparameters described in Section 7 can be achieved.5.2.1 Burette,to titrate hydrochloric acid(c=0.1 mol/dm3),and5.2.2 Burette,to titrate sodium hydroxide standard solution(c=0.1 mol/dm3).1This test met
14、hod 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 Nov.1,2022.Published November 2022.Originallyapproved in 2015.Last previous edition approved
15、in 2018 as D8016 181.DOI:10.1520/D8016-22.2For 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.3G.W.Sears,Anal.Chem.,19
16、81-1983,1956.4Appropriate devices are commercially available.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.15.3 pH electrode
