1、Designation: D8016 18Standard 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, 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
5、 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:2D4483 Practice for Evaluat
6、ing Precision for Test 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 toS
7、ears,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 solu-tion. The initial preliminary treatment step consists of exposureof the silica to a sufficiently concentrated solutio
8、n 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 containing 150 cm3NaCl solution adjusted to pH 3. Thesuspension is stirred for 3 min and brought to 25C. Thesuspension
9、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 corrected with the volatile matter deter-mined according to Test Method D6738. The consumption ofsodium hydroxi
10、de 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 primarily on the silica surface area, thedensity of the silanol groups, and the degree of hydrophobicity.4. Signific
11、ance 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 thesilica during the processing step called silanization. Silane-coupling agents are multifunctional mole
12、cules 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 performing avolumetric endpoint titration based on pH, as well as equippedwith data storage and calcu
13、lation 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 Beakers, glass, 250 cm3.1This test method is under the jurisdiction of ASTM Committee D11 on Rubb
14、erand Rubber-like Materials and is the direct responsibility of Subcommittee D11.20on Compounding Materials and Procedures.Current edition approved June 1, 2018. Published October 2018. Originallyapproved in 2015. Last previous edition approved in 2015 as D8016 15. DOI:10.1520/D8016-18.2For referenc
15、ed 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., 1981-1983, 1956.4Appropriate devices are commer
16、cially 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 theDev
17、elopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.6 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 cm3fo
18、r determination of the actualconcentration of the sodium hydroxide standard solution.5.10 Analytical Balance, 0.1 mg sensitivity.5.11 Magnetic Stirrer with Stir Bar.5.12 Graduated Cylinder, 250 cm3.5.13 Beaker, glass, 2 dm3.5.14 Volumetric Flask, 2dm3.6. Reagents and Materials6.1 Purity of ReagentsR
19、eagent-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,provided it is first as
20、certained 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 hydrochloric acid, c =1 mo
21、l/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 Solution (NaOH), 0.1 mol
22、/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 Number induplicate o
23、r 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 Determination of the Actual
24、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 solutionshould be valida
25、ted 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 cm3ofdeionized water. Brin
26、g 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:cACTUAL= actual concen
27、tration 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 Blank Reading of the N
28、aCl 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 cm3titration beaker.7.4.
29、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 method for the blank
30、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 consumption of sodium hydr
31、oxide 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 (pH 3) using a gradu
32、atedcylinder 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.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Su
33、ggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D8016 1827.5.4 Place the ti
34、tration beaker on the automated titrator andcheck the pH. If the initial 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 ra
35、te: 50 L/min, and maximum rate: 500 L/minand endpoint 2 at pH 9: control range pH: 0.2, minimum rate:15 L/min, and maximum rate: 2000 L/min, switch-off delay:3s.8. Calculation of Results8.1 When titration is finished, the titration curve and thefollowing results are displayed by the titrator.8.2 If
36、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 VBR!SCACTUALCNOMINAL
37、DS100100 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 solu-tion in mol/dm
38、3, 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 Bias610.1 This precision and bias section has been prepared inaccordance with Practice D4483-99, which sh
39、ould be referredto for terminology and other statistical calculation details.10.2 A Type 1 interlaboratory precision was evaluated inMarch 2016. Both repeatability and reproducibility are short-term. Triplicate determinations were made on each of the testsilicas on a single day. A test result, as sp
40、ecified by this testmethod, is a single determination of the Sears Number.10.3 The precision statement was determined through sta-tistical examination of test results reported by 9 of the 12participating laboratories, on three silica materials. Thesamples tested were described as:Sample 1: Granulate
41、, medium level of Sears Number.Sample 2: Powder, high level of Sears Number.Sample 3: Powder, low level of Sears Number.10.4 To judge the equivalency of two test results, it isrecommended to choose the sample type closest in character-istics to one of the test silicas described.10.5 The results of t
42、he precision calculations for repeatabil-ity and reproducibility are given in Table 1 for each of thesilicas evaluated.10.6 Repeatability, r, and reproducibility, R, vary over therange of surface areas measured. The preferred precision isshown in bold text in Table 1.10.7 RepeatabilityThe pooled rel
43、ative repeatability, (r),of this test method has been established as 3.3 %. Any otherappropriate value tabulated in Table 1 may also be used toestimate repeatability. Two single test results, obtained withthis test method on the same instrument and with the sameoperator, that differ by more than the
44、 tabulated r or (r) (for anygiven mean Sears Number) must be considered as derived fromdifferent or non-identical sample populations and some appro-priate action taken.NOTE 1Appropriate action may be an investigation of the test methodprocedure or apparatus for faulty operation or the declaration of
45、 asignificant difference in the two materials, samples, etc., which generatedthe two test results.10.8 ReproducibilityThe pooled relative reproducibility,(R), of this test method has been established as 17.4 %. Anyother appropriate value tabulated in Table 1 may also be usedto estimate reproducibili
46、ty. Two single test results obtainedwith this test method, in two different laboratories, that differby more than the tabulated R or (R) (for any given meansurface area) must be considered as derived from different ornon-identical sample populations and some appropriate actiontaken.6A research repor
47、t is pending.TABLE 1 Precision Parameters for D8016, Silica, Precipitated, HydratedSears Number, (Type 1 Precision)NOTE 1 Preferred precision shown in bold text.Units Sears Num-berMaterial Period Number ofLaboratories(M/H/L)AMean Level Sr r (r) SR R (R)Sample 1 Unknown 9(1/1/0) 11.3 0.09 0.26 2.3 0.
48、53 1.51 13.4Sample 2 Unknown 9(1/1/0) 17.4 0.17 0.49 2.8 1.04 2.94 17.0Sample 3 Unknown 9(1/0/0) 7.5 0.14 0.39 5.2 0.52 1.48 19.8Average 12.0Pooled Values 0.14 0.39 3.3 0.74 2.09 17.4AM = number of outliers for Mean; H = number of outliers for High variation; L = number of outliers for Low variation
49、.D8016 18310.9 BiasBias is the difference between a test value and areference value. However, for this test method, bias has notbeen determined.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 advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is s
