1、Designation:D801615Standard 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D6738 Test Method for Precipitated SilicaVolatile Con-tent3.Summary of Test Method3
5、.1 An ion exchange reaction in silica is possible based onthe acidic character of the surface silanol groups.According toSears,3it is possible to determine the surface area of colloidalsilica on the basis of this ion exchange mechanism,aftercertain preliminary treatments,by titration with a basic so
6、lu-tion.The initial preliminary treatment step consists of exposureof the silica to a sufficiently concentrated solution of sodiumchloride(NaCl).After 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 co
7、ntaining 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 then 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
8、corrected with the volatile matter deter-mined according to Test Method D6738.The consumption ofsodium hydroxide solution minus the blank reading withoutsilica is defined as the Sears Number given in cm3/1.5 g.Thespecific consumption of sodium hydroxide solution in a silicasuspension depends primari
9、ly on the silica surface area,thedensity of the silanol groups,and the degree of hydrophobicity.4.Significance and Use4.1 The rubber-filler interaction 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
10、 thesilica during the processing step called silanization.Silane-coupling agents are multifunctional molecules able to createmolecular bridges between the elastomer or rubber matrix andthe silica surface.5.Apparatus5.1 Precision Balance,0.01 g sensitivity.5.2 Automatic Titration Apparatus,capable of
11、 performing avolumetric endpoint titration based on pH,as well as equippedwith data storage and calculation modules.45.2.1 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).5.3 pH electrode.5.4 Printer(optional).5.5 Beak
12、ers,glass,250 cm3.5.6 Laboratory Grinder,for example,electro-mechanical.5.7 Wire Mesh Sieve,75 m(200 mesh).5.8 Thermostated water bath.5.9 Titration Beaker,150 cm3for determination of the actualconcentration of the sodium hydroxide standard solution.5.10 Analytical Balance,0.1 mg sensitivity.5.11 Ma
13、gnetic Stirrer with Stir Bar.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.20 on Compounding Materialsand Procedures.Current edition approved Nov.1,2015.Published December 2015.DOI:10.1520/D8016-15.2For referenced ASTM
14、 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.,1981-1983,1956.4Appropriate devices are commercially available.C
15、opyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.12 Graduated Cylinder,250 cm3.5.13 Beaker,glass,2 dm3.5.14 Volumetric Flask,2 dm3.6.Reagents and Materials6.1 Purity of ReagentsReagent-grade chemicals shall beused in all tests.Unless othe
16、rwise indicated,it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.5Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.6.2 NaCl SolutionDissolve 400 g analytical grade NaCl inapproximately 1.75 dm3deionized water in a 2 dm3beaker.Adjust the solution to pH
