1、Designation: D 6845 02Standard Test Method forSilica, Precipitated, HydratedCTAB(Cetyltrimethylammonium Bromide) Surface Area1This standard is issued under the fixed designation D 6845; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、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 thes
4、tandard. 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 and health practices and determine the appl
5、ica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1193 Specification for Reagent Water2D 1799 Practice for Carbon BlackSampling PackagedShipments3D 1900 Practice for Carbon BlackSampling Bulk Ship-ments3D 4483 Practice for Determining Precision for Test Me
6、thodStandards in the Rubber and Carbon Black Industries33. 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. Th
7、e 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 OT4) solution to a turbidity maximum end pointis used to determine the unadsorbed CTA
8、B 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
9、, 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,5chemically resistant covered (poly-chlorotrifluoroethylene
10、 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,50cm3,
11、 0.1 cm3divisions, Class A, preferably ofautomatic refilling and zeroing type (see Note 1) with reagentreservoir.NOTE 1Automatic 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 s
12、hould be prepared andused to correct observed buret readings. Burets with TFE-fluorocarbonmanostat valves offer some advantage in ease of stopcock manipulation indelivering small increments of titrant.5.7 Dispenser-Type Pipet,650 cm3, attached to a suitablereservoir for CTAB solution.1This test meth
13、od 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 Dec. 10, 2002. Published December 2002. Originallyapproved in 2002. Last previous edition approved in 2002 as D 6845 02.
14、2Annual Book of ASTM Standards, Vol 11.01.3Annual Book of ASTM Standards, Vol 09.01.4Aerosol OT is a registered trademark of the American Cyanamid Co., ProcessChemicals Dept., Wayne, NM 07470.5Examples of suitable spinbars are Catalog No. 9235-U7, A. H. Thomas Co.,Philadelphia, PA 19105, or Catalog
15、No. S-76497-30, Sargent Welch Scientific Co.,Skokie, IL 60076.6This test is based on the use of the Universal Repipet, a registered trademarkof Labindustries, 1802 Second St., Berkeley, CA 94710.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Unit
16、ed States.5.8 Pipet,10cm3, Class A.5.9 Erlenmeyer Flasks, or beakers, 50 or 100 cm3.5.10 Dropping Bottle,60cm3amber.5.11 Jar, wide-mouth, plastic screw cap, 120 or 240 cm3(4-or 8-oz) size.5.12 Gravity Convection Drying Oven, capable of maintain-ing 105 6 5C.5.13 Magnetic Stirrer.5.14 Containers, sui
17、table for preparation and storage ofreagent solutions.5.15 Automatic Titration Equipment with 550 nm Photo-probe,7with instruction manual.5.16 Beakers, 100 cm3Berzelius, tall form (one furnishedwith automatic titration equipment).5.17 Thermometer, to measure temperature in a range from20 to 40C.5.18
18、 Polyethylene Tubing (do not use vinyl tubing).NOTE 2All apparatus must be kept chemically clean. Contaminationof equipment, water supply, or chemicals by ionic surfactants must beparticularly avoided.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwis
19、e indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.8Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permi
20、t its use without lessening the accuracy ofthe determination.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water as definedby Type 1 in Specification D 1193.6.3 Sodium Hydroxide Solution (1M)Dissolve 40.0 gNaOH ina1dm3flask containing 0.5 dm3re
21、agent water. Afterdissolution fill to mark.6.4 Buffer Solution of pH 9.6 (0.05 M)Prepare buffersolution by dissolving 3.101 g of orthoboric acid (H3BO4),3.708 g of potassium chloride (KCl) and 36.85 cm3of sodiumhydroxide (NaOH) solution ina1dm3flask containing 0.5 dm3reagent water. After dissolution
22、 fill to mark. Verify that the pHof the solution is 9.6 6 0.1.6.5 CTAB Standard SolutionDissolve 5.5 g of reagent-grade CTAB9ina1dm3flask containing 350 dm3of buffersolution and 500 dm3water. After dissolution fill to mark.Homogenize on a magnetic stirrer for 10 h. Allow to stand 24h before use. Ver
23、ify that the pH of the solution is 9.6 6 0.1before use. If not, adjust the pH with either 0.1 N NaOHsolution (too low) or 0.1 N HCl solution (too high).(WarningStorage of the solution below 22C will result inslow crystallization of the CTAB.)6.6 Aerosol OT10Solution 100 % Grade (approximately0.00389
24、 M)Dissolve 1.73 g/dm3of Aerosol OT solution(100 % solids) in 500 cm3distilled or deionized water. Stirvigorously with a magnetic stirrer for 10 h. Allow to stand anadditional twelve days before standardization and use. Thesolution should be capped tightly and stored in a cool place.(Once opened, 10
25、0 % Aerosol OT should be stored in adesiccator.)6.7 Distilled or Deionized Water.6.8 Octylphenoxy Polyethoxyethanol (Triton X-10011) Solu-tion (0.15 %)Dissolve 1.5 g in 1 dm3of Triton X-100 (100 %liquid) in distilled or deionized water by swirling vigorouslywith a magnetic stirrer until a homogeneou
26、s solution isobtained.7. Sampling7.1 No separate practice for sampling silicas is available.However, samples may be taken in accordance with PracticesD 1799 or D 1900.8. Standardization of Reagents8.1 Duplicate blanks are determined and averaged.8.2 Pipet 10 cm3of CTAB solution into a beaker.8.3 Add
27、 50 cm3of distilled or deionized water.8.4 Titrate with Aerosol OT using automatic titrator untilendpoint is reached.8.5 Use average of both repetitions when calculating CTABof silica sample in Section 10.9. Procedure9.1 Dry an adequate portion of sample of silica at 105C for2 h and cool in a desicc
28、ator.NOTE 3If the heating loss of the silica is known, the drying step maybe omitted and the observed sample mass corrected for heating loss toobtain the mass of dry sample, W.9.2 Weigh, to 0.1 mg, a suitable sample of the dried silicainto a glass vial and record the mass as W. Appropriate samplemas
29、ses may be selected as follows:Approximate SurfaceArea, m2/g (SA)Sample Mass,gSA # 90 0.60090SA# 120 0.500120SA# 175 0.400175SA# 220 0.300220 SA 0.200An appropriate sample mass may also be taken as Vo/Sesting, where Sestis some estimate of the expected CTAB surfacearea.7This test is based on the use
30、 of two sources of automatic titration equipment:(1) Mettler Memotitrator DL21, Mettler Instrument Co., Box 71, Highstown, NJ08520, and (2) Brinkman Dosimat 665 Buret, Brinkman Instruments, Inc., Canti-ague Rd., Westbury, NY. The Probe Colorimeter, also available from BrinkmanInstruments, has been f
31、ound to be an acceptable automatic means of detecting thetitration end point. This piece of equipment may be integrated with the BrinkmanDosimat 665 Buret.8Reagent Chemicals, American Chemical Society Specifications, Am. ChemicalSoc., Washington, DC. For suggestions on the testing of reagents not li
32、sted by theAmerican Chemical Society, see Reagent Chemicals and Standards, by JosephRosin, D. Van Nostrand Co., Inc., New York, NY, and the United States Pharma-copeia.9Available from J. T. Baker Chemical Co., 222 Red School Lane, Phillipsburgh,NJ 08865, Catalog No. 7N121.10Available from American C
33、yanamid Co., Process Chemicals Dept., Wayne,NM 07470. Also available as Catalog No. A-349 from Fisher Scientific Co.11Triton X-100 is a registered trademark of Rohm and Haas Co.D68450229.3 Insert a magnetic spinbar into the vial. Add 30.0 cm3ofCTAB solution from the dispensing pipet or buret taking
34、careto prevent foaming of the solution. Cap the vial.9.4 Place the vial on a magnetic stirrer. Adjust the stirrer togive a vigorous stirring by the spinbar to produce a deep votexwithout foaming. Stir for 40 min.9.5 Immediately after completion of the stirring, decant thesuspension into a centrifuge
35、 tube.9.6 Separate the silica from the suspension by centrifugingfor 20 min at 4000 rpms.9.7 Pipet a 10.00 cm3aliquot of the CTAB solution from thecentrifuge tube into a 100 cm3beaker containing a TFE-fluorocarbon covered magnetic spin bar 41 mm long by 10 mmin diameter (1.625 by 0.375 in.), taking
36、care to avoid transfer-ring any silica.9.8 Titration (Automatic):9.8.1 Prepare the automatic titration apparatus according tothe instructions furnished with it. Ascertain that the titrantreservoir contains sufficient Aerosol OT solution and that thefluid lines and the pump head are free of air bubbl
37、es and havebeen flushed sufficiently with titrant. Turn the power on andloosen the titrant reservoir cap to admit air as liquid flows out.Adjust the titrant flow rate to 10 cm3/min.9.8.2 Lower the 550 nm photo probe into the solution.9.8.3 Lower the titrant delivery assembly so that the deliv-ery ne
38、edle is just below the surface of the liquid and open thetitrant stopcock.9.8.4 Set the pump control switch to the “titrate” positionand press the “start” button.9.8.5 After the system stops record the amount of OTdispensed.9.8.6 Raise the titrant delivery tube clear of the beaker.9.8.7 Move the pum
39、p control to “flush” and allow a fewdrops of titrant to clear the needle. After the pump stops, closethe stopcock and remove the needle from the beaker. Wipe theneedle with a clean tissue (do not use solvent).9.8.8 Remove and rinse the photoprobe with distilled water.9.8.9 The unit is now ready for
40、another sample.10. Calculation10.1 Calculate the CTAB surface area to the nearest 0.1 3103m2/g as follows:S 5 2V02 V! 3 4774 / V03 W100 2 Vol!# (1)where:S = CTAB surface area of dried silica, 103m2/g,V0= volume of OT required to titrate 5 cm3of CTAB(Blank),V = aerosol OT solution required for the 10
41、 cm3sample,W = sample mass, g, andVol = volatile matter of silica, %.11. Report11.1 Report the following information:11.1.1 Proper identification of the silica sample and11.1.2 Result obtained from an individual determination,reported to the nearest 0.1 3 103m2/g.12. Precision and Bias12.1 Precision
42、 and bias statements have not been generated.13. Keywords13.1 cetyltrimethylammonium bromide; CTAB; silica; sur-face area by CTAB method; turbidity titrationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standar
43、d. 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 subject to revision at any time by the responsible technical committee and must be reviewed
44、 every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible t
45、echnical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D6845023
