1、Designation: D8016 15Standard 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
2、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 is used to determine the number ofsilanol groups on the surface of silica by titration according toa method as developed by S
3、ears. This test 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 w
4、ith its use. It is 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. Summ
5、ary 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 determine the surface area of colloidalsilica on the basis of this ion exchange mechanism, aftercertain preliminary treatments, by tit
6、ration with a basic solu-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 weighe
7、d 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 then to pH 9 using asodium hydroxide solution (c = 0.1 mol/dm3). The volume ofsodium hydroxide solution that is reacted between
8、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 withoutsilica is defined as the Sears Number given in cm3/1.5 g. Thespecific consumption of sodium hydroxide solution in a
9、 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 interaction needed in silica technologyfor the rubber industry is based on the use of silane-couplingagents that react with
10、the silanol groups on the surface of 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 A
11、utomatic Titration Apparatus, capable of 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)
12、.5.3 pH electrode.5.4 Printer (optional).5.5 Beakers, 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 sol
13、ution.5.10 Analytical Balance, 0.1 mg sensitivity.5.11 Magnetic 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. Publi
14、shed December 2015. DOI:10.1520/D8016-15.2For 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.
15、Chem., 1981-1983, 1956.4Appropriate devices are commercially available.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.12 Graduated Cylinder, 250 cm3.5.13 Beaker, glass, 2 dm3.5.14 Volumetric Flask, 2dm3.6. Reagents and Materials6.1
16、 Purity of ReagentsReagent-grade chemicals shall beused in all tests. Unless otherwise 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,pro
17、vided 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 ina2dm3beaker.Adjust the solution to pH 3 (60.1) with hydroc
18、hloric acid, c =1 mol/dm3, and transfer the solution toa2dm3volumetricflask. When the temperature has reached 25C, fill the volu-metric flask to the calibration mark and mix well using thestirrer bar and the magnetic stirrer.6.3 Hydrochloric Acid (HCl), 0.1 mol/dm3.6.4 Sodium Hydroxide Standard Solu
19、tion (NaOH), 0.1 mol/dm3.6.5 Deionized Water.6.6 Buffer Solutions, pH of 4, 7, and 9.6.7 Potassium Hydrogen Phthalate, primary standard.7. Procedure7.1 Grind an appropriate quantity of silica sample in alaboratory grinder for 60 s. Approximately 6 to8garerecommended for a determination of the Sears
20、Number induplicate or in triplicate, respectively.7.2 Pass ground sample (see 7.1) through a wire mesh sieve75 m (200 mesh). This can be accomplished manually ormechanically. Discard fraction retained on sieve. The fraction75 m (200 mesh) is used for the determination of the SearsNumber.7.3 Determin
21、ation of the Actual Concentration of the NaOHStandard Solution:7.3.1 If the method is used regularly, the concentration ofthe NaOH standard solution is determined at least every monthor as needed with three replicate determinations. Otherwise, itis recommended that the concentration of the NaOH solu
22、tionshould be validated before use regardless of the storage time.7.3.2 To determine the concentration of the NaOH solution,weigh between 0.1 and 0.2 g potassium hydrogen phthalateaccurately to 0.1 mg into a 150 cm3titration beaker. Dissolvethe potassium hydrogen phthalate in approximately 75 cm3ofd
23、eionized water. Bring the solution to 25C in a water bath.Titrate potentiometrically to endpoint with the NaOH standardsolution. The endpoint is indicated by steepest slope betweenpH 7 and pH 9.7.3.3 Calculate the actual concentration of the NaOH stan-dard solution:CACTUAL5mKHPMKHP3 VNaOH(1)where:cA
24、CTUAL= actual concentration of sodium hydroxide solu-tion in mol/dm3,mKHP= mass of potassium hydrogen phthalate in mg,MKHP= molar weight of potassium hydrogen phthalate;204.22 g/mol, andVNaOH= volume of sodium hydroxide solution consumedin cm3, 1000 cm3correspond to 1 dm3.7.4 Determination of the Bl
25、ank Reading of the NaCl Solu-tion (pH 3):7.4.1 Before measuring the silica sample, carry out a doubledetermination of the blank reading of the NaCl solution, that is,performing the titration without silica.7.4.1.1 Use a graduated cylinder to transfer 150 cm3of theNaCl solution (pH 3) into a 250 cm3t
26、itration beaker.7.4.1.2 Stir the solution for approximately 1 min and bringthe temperature to 25.0 6 0.5C.7.4.2 Calibrate the pH electrode using the buffer solutionspH 4, 7, and 9.7.4.3 Place a stirring bar in the solution and place thetitration beaker on the titrator.7.4.4 Start the corresponding m
27、ethod for the blank readingon the automated titrator. The following settings are recom-mended: endpoint 1 at pH 4: control range pH: 0.6, minimumrate: 10 L/min, and maximum rate: 100 L/min and endpoint2 at pH 9: control range pH: 2, minimum rate: 10 L/min, andmaximum rate: 200 L/min.7.4.5 The consum
28、ption of sodium hydroxide solution toraise the pH from 4.0 to 9.0 is noted as blank reading VBR.7.5 Determination of the Sears Number (Tested in Dupli-cate):7.5.1 Weigh 1.50 6 0.01 g of the silica sample into a 250cm3titration beaker on a precision or analysis balance.7.5.2 Add 150 cm3NaCl solution
29、(pH 3) using a graduatedcylinder and then place a stirring bar in the vessel.7.5.3 Stir the suspension with a magnetic stirrer for about 2min and then bring it up to a temperature of 25.0 6 0.5C ina water bath.7.5.4 Place the titration beaker on the automated titrator andcheck the pH. If the initial
30、 pH is above pH 4 titrate with theHCl solution, c = 0.1 mol/dm3to pH of 3.95 before proceeding.7.5.5 Start the Sears Number titration. The following set-tings are recommended: endpoint 1 at pH 4: control range pH:0.2, minimum rate: 50 L/min, and maximum rate: 500 L/minand endpoint 2 at pH 9: control
31、 range pH: 0.2, minimum rate:15 L/min, and maximum rate: 2000 L/min, switch-off delay:3s.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards
32、 for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D8016 1528. Calculation of Results8.1 When titration is finished, the titration curve and thefollowing results are displayed by
33、the titrator.8.2 If the calculation function of the titrator is not used, allrelevant data (actual concentration of NaOH standard solution,NaOH consumption between pH 4 and 9, blank reading,volatile matter, and initial pH) are to be considered for thecalculation of the Sears Number, SN:SN 5 VpH4292
34、VBR!SCACTUALCNOMINALDS100100 2 VMD(2)where:VpH 49= volume of NaOH solution consumed to raisethe pH from 4.0 to 9.0 in cm3,VBR= volume of NaOH solution consumed for theblank in cm3,CNOMINAL= nominal concentration (=0.1000 mol/dm3)ofNaOH standard solution,CACTUAL= actual concentration of NaOH standard
35、 solu-tion in mol/dm3, andVM = volatile matter according to Test MethodD6738 in percent.9. Report9.1 Identification of the silica sample.9.2 Sears Number in cm3/1.5 g (reporting: one decimalplace).10. Precision and Bias10.1 Precision and bias statements have not been generatedbut will be available w
36、ithin five years of publication of the testmethod.11. Keywords11.1 Sears Number; silane; silanol groups; silicaASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advise
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