1、Designation:D684502 (Reapproved 2008) Designation: D6845 12Standard Test Method forSilica, Precipitated, HydratedCTAB(Cetyltrimethylammonium Bromide) Surface Area1This standard is issued under the fixed designation D6845; the number immediately following the designation indicates the year oforiginal
2、 adoption or, in the case of revision, the year of last revision. A number 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 covers the measurement of the specific surface are
3、a of precipitated silicas exclusive of area contained inmicropores too small to admit hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, commonly referred toas CTAB) molecules. This test method is suitable for characterizing rubber-grade silicas of all types.1.2 The values stated in
4、 SI units are to be regarded as the standard. The values given in parentheses are for information only.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and h
5、ealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1799 Practice for Carbon BlackSampling Packaged ShipmentsD1900 Practice for Carbon BlackSampling Bulk ShipmentsD4483 Practice for Eva
6、luating Precision for Test Method Standards in the Rubber and Carbon Black Manufacturing IndustriesPractice for Evaluating Precision for Test Method Standards in the Rubber and Carbon Black Manufacturing IndustriesE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practic
7、e for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Summary of Test Method3.1 The isotherm for adsorption of an aqueous solution of CTAB on silicas has a long horizontal plateau corresponding to amonolayer coverage of the substrate surface from which the adsorbate
8、 is not sterically excluded. The CTAB adsorption by silicais independent of functional groups containing hydrogen and oxygen, etc. Rapid equilibration is achieved by using mechanicalstirring. Titration with dioctyl sodium sulfosuccinate (Aerosol OT3) solution to a turbidity maximum end point is used
9、 to determinethe unadsorbed CTAB after removal of the colloidally dispersed silica by ultrafiltration.3.2 Titration of the unadsorbed CTAB with Aerosol OT solution is accomplished by automatic titration.4. Significance and Use4.1 The CTAB molecule is relatively large; so it is not adsorbed in microp
10、ores or on surface roughness. Thus, the CTAB surfacearea reflects only the surface of the silica that is available 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,4chemically resistant co
11、vered (polychlorotrifluoroethylene or TFE-fluorocarbon), 6.4- or 4.8-mm (14-or316-in.) diameter, and length nearly equal to the diameter of 50 or 100 cm3Berzelius beakers, glass vials, or other glass vessels.1This test method is under the jurisdiction of ASTM Committee D11 on Rubber and is the direc
12、t responsibility of Subcommittee D11.20 on Compounding Materials andProcedures.Current edition approved Jan. 15, 2008.1, 2012. Published February 2008.2012. Originally approved in 2002. Last previous edition approved in 20022008 as D6845 02(2008). DOI: 10.1520/D6845-02R08.10.1520/D6845-12.2For refer
13、enced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3Aerosol OT is a registered trademark of the American Cyanamid Co., P
14、rocess Chemicals Dept., Wayne, NM 07470.4Examples of suitable spinbars are Catalog No. 9235-U7, A. H. Thomas Co., Philadelphia, PA 19105, or Catalog No. S-76497-30, Sargent Welch Scientific Co., Skokie,IL 60076.1This document is not an ASTM standard and is intended only to provide the user of an AST
15、M standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published
16、by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.4 Glass Funnel, small.5.5 Glass Vials, with plastic screw caps, 28 mm in outside diameter, about 40 cm3capacity.5.6 Buret,50cm3, 0.1 c
17、m3divisions, Class A, preferably of automatic refilling and zeroing type (see Note 1) with reagentreservoir.NOTE 1Automatic burets are usually not certified to Class A tolerance. Such burets should be checked for accuracy, and if in error by more than 0.05cm3at any point, a calibration curve should
18、be prepared and used to correct observed buret readings. Burets with TFE-fluorocarbon manostat valves offersome advantage in ease of stopcock manipulation in delivering small increments of titrant.5.7 Dispenser-Type Pipet,550 cm3, attached to a suitable reservoir for CTAB solution.5.8 Pipet,10cm3, C
19、lass 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 maintaining 105 6 5C.5.13 Magnetic Stirrer.5.14 Containers, suitable for preparation and st
20、orage of reagent solutions.5.15 Automatic Titration Equipment with 550 nm Photoprobe,6with instruction manual.5.16 Beakers, 100 cm3Berzelius, tall form (one furnished with automatic titration equipment).5.17 Thermometer, to measure temperature in a range from 20 to 40C.5.18 Polyethylene Tubing (do n
21、ot use vinyl tubing).NOTE 2All apparatus must be kept chemically clean. Contamination of equipment, water supply, or chemicals by ionic surfactants must beparticularly avoided.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is inten
22、ded that allreagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.7Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without less
23、ening the accuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water as defined byType 1 in Specification D1193.6.3 Sodium Hydroxide Solution (1M)Dissolve 40.0 g NaOH ina1dm3flask containing 0.5 dm3reagent water. Afterdi
24、ssolution fill to mark.6.4 Buffer Solution of pH 9.6 (0.05 M)Prepare buffer solution by dissolving 3.101 g of orthoboric acid (H3BO4), 3.708 g ofpotassium chloride (KCl) and 36.85 cm3of sodium hydroxide (NaOH) solution ina1dm3flask containing 0.5 dm3reagent water.After dissolution fill to mark. Veri
25、fy that the pH of the solution is 9.6 6 0.1.6.5 CTAB Standard SolutionDissolve 5.5 g of reagent-grade CTAB8ina1dm3flask containing 350 dm3of buffer solutionand 500 dm3water.After dissolution fill to mark. Homogenize on a magnetic stirrer for 10 h.Allow to stand 24 h before use. Verifythat the pH of
26、the solution is 9.6 6 0.1 before use. If not, adjust the pH with either 0.1 N NaOH solution (too low) or 0.1 N HClsolution (too high). (Warning Storage of the solution below 22C will result in slow crystallization of the CTAB.)6.6 Aerosol OT9Solution 100 % Grade (approximately 0.00389 M)Dissolve 1.7
27、3 g/dm3of Aerosol OT solution (100 %solids) in 500 cm3distilled or deionized water. Stir vigorously with a magnetic stirrer for 10 h. Allow to stand an additional twelvedays before standardization and use. The solution should be capped tightly and stored in a cool place. (Once opened, 100 %AerosolOT
28、 should be stored in a desiccator.)6.7 Distilled or Deionized Water.6.8 Octylphenoxy Polyethoxyethanol (Triton X-10010) Solution (0.15 %)Dissolve 1.5 g in 1 dm3of Triton X-100 (100 %liquid) in distilled or deionized water by swirling vigorously with a magnetic stirrer until a homogeneous solution is
29、 obtained.7. Sampling7.1 No separate practice for sampling silicas is available. However, samples may be taken in accordance with Practices D1799or D1900.5This test is based on the use of the Universal Repipet, a registered trademark of Labindustries, 1802 Second St., Berkeley, CA 94710.6This test i
30、s based on the use of two sources of automatic titration equipment: (1) Mettler Memotitrator DL21, Mettler Instrument Co., Box 71, Highstown, NJ 08520,and (2) Brinkman Dosimat 665 Buret, Brinkman Instruments, Inc., Cantiague Rd., Westbury, NY. The Probe Colorimeter, also available from Brinkman Inst
31、ruments, has beenfound to be an acceptable automatic means of detecting the titration end point. This piece of equipment may be integrated with the Brinkman Dosimat 665 Buret.7Reagent Chemicals, American Chemical Society Specifications , Am. Chemical Soc., Washington, DC. For suggestions on the test
32、ing of reagents not listed by theAmerican Chemical Society, see Reagent Chemicals and Standards, by Joseph Rosin, D. Van Nostrand Co., Inc., New York, NY, and the United States Pharmacopeia .8Available from J. T. Baker Chemical Co., 222 Red School Lane, Phillipsburgh, NJ 08865, Catalog No. 7N121.9Av
33、ailable from American Cyanamid Co., Process Chemicals Dept., Wayne, NM 07470. Also available as Catalog No. A-349 from Fisher Scientific Co.10Triton X-100 is a registered trademark of Rohm and Haas Co.D6845 1228. Standardization of Reagents8.1 Duplicate blanks are determined and averaged.8.2 Pipet 1
34、0 cm3of CTAB solution into a beaker.8.3 Add 50 cm3of distilled or deionized water.8.4 Titrate with Aerosol OT using automatic titrator until endpoint is reached.8.5 Use average of both repetitions when calculating CTAB of silica sample in Section 10.9. Procedure9.1 Dry an adequate portion of sample
35、of silica at 105C for 2 h and cool in a desiccator.NOTE 3If the heating loss of the silica is known, the drying step may be omitted and the observed sample mass corrected for heating loss to obtainthe mass of dry sample, W.9.2 Weigh, to 0.1 mg, a suitable sample of the dried silica into a glass vial
36、 and record the mass as W.Appropriate sample massesmay be selected as follows:Approximate SurfaceArea, m2/g (SA)Sample Mass,gSA # 90 0.60090SA# 120 0.500120SA# 175 0.400175SA# 220 0.300220SA 0.200An appropriate sample mass may also be taken as Vo/Sestin g, where Sestis some estimate of the expected
37、CTAB surface area.9.3 Insert a magnetic spinbar into the vial. Add 30.0 cm3of CTAB solution from the dispensing pipet or buret taking care toprevent foaming of the solution. Cap the vial.9.4 Place the vial on a magnetic stirrer. Adjust the stirrer to give a vigorous stirring by the spinbar to produc
38、e a deep votexwithout foaming. Stir for 40 min.9.5 Immediately after completion of the stirring, decant the suspension into a centrifuge tube.9.6 Separate the silica from the suspension by centrifuging for 20 min at 4000 rpms.9.7 Pipet a 10.00 cm3aliquot of the CTAB solution from the centrifuge tube
39、 into a 100 cm3beaker containing aTFE-fluorocarbon covered magnetic spin bar 41 mm long by 10 mm in diameter (1.625 by 0.375 in.), taking care to avoidtransferring any silica.9.8 Titration (Automatic):9.8.1 Prepare the automatic titration apparatus according to the instructions furnished with it. As
40、certain that the titrant reservoircontains sufficient Aerosol OT solution and that the fluid lines and the pump head are free of air bubbles and have been flushedsufficiently with titrant. Turn the power on and loosen the titrant reservoir cap to admit air as liquid flows out. Adjust the titrantflow
41、 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 delivery needle is just below the surface of the liquid and open the titrantstopcock.9.8.4 Set the pump control switch to the “titrate” position and press the “start” button
42、.9.8.5 After the system stops record the amount of OT dispensed.9.8.6 Raise the titrant delivery tube clear of the beaker.9.8.7 Move the pump control to “flush” and allow a few drops of titrant to clear the needle. After the pump stops, close thestopcock and remove the needle from the beaker. Wipe t
43、he needle 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 another sample.10. Calculation10.1 Calculate the CTAB surface area to the nearest 0.1 3 103m2/g as follows:S 5 2V02 V! 3 4774 / V03 W100 2 Vol!# (1)TABLE 1 CT
44、AB Surface Area (m2g)Material AverageARepeatabilityStandardDeviationReproducibilityStandardDeviationRepeatabilityLimitReproducibilityLimitx srsRr RSilica A 161.4 1.17 3.19 3.27 8.93Silica B 194.2 1.03 7.58 2.88 21.21AThe average of the laboratories calculated averages.D6845 123where:S = CTAB surface
45、 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 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 a
46、nd11.1.2 Result obtained from an individual determination, reported to the nearest 0.1 3 103m2/g.12. Precision and Bias12.1Precision and bias statements have not been generated.1112.1 The precision of this test method is based on an interlaboratory study conducted in 2010. Nine laboratories tested t
47、wo typesof silica samples. Every “test result” represents an individual determination. Each laboratory was instructed to report four replicatetest results for each material. Practice E691 was followed for the design and analysis of the data.12.1.1 Repeatability Limit (r)Two test results obtained wit
48、hin one laboratory shall be judged not equivalent if they differ bymore than the “r” value for that material; “r” is the interval representing the critical difference between two test results for the samematerial, obtained by the same operator using the same equipment on the same day in the same lab
49、oratory.12.1.1.1 Repeatability limits are listed in Table 1.12.1.2 Reproducibility Limit (R)Two test results shall be judged not equivalent if they differ by more than the “R” value forthat material; “R” is the interval representing the critical difference between two test results for the same material, obtained bydifferent operators using different equipment in different laboratories.12.1.2.1 Reproducibility limits are listed in Table 1.12.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.12.1.4 Any
