1、Designation: D6845 12D6845 18Standard 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 adoption or, in the case of r
2、evision, 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 area of precipitated silicas excl
3、usive 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 SI units are to be regarded a
4、s 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 safety, health, and healthenvironme
5、ntal practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guid
6、es and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1799 Practice for Carbon BlackSampling Packaged ShipmentsD1900 Practice for Carbon BlackSampling Bulk ShipmentsD44
7、83 Practice 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 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Summary
8、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 is not sterically excluded. The CTAB adsorption by silicais independent of functional groups co
9、ntaining 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 to determinethe unadsorbed CTAB after removal of the colloidally dispersed silica by ultrafiltr
10、ation.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 micropores or on surface roughness. Thus, the CTAB surfacearea reflects only the surface of the silica
11、 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).1 This test method is under the jurisdiction of ASTM Committee D11 on Rubber and Rubber-like Materials and is the direct responsibility of Sub
12、committee D11.20 onCompounding Materials and Procedures.Current edition approved Jan. 1, 2012Feb. 1, 2018. Published February 2012March 2018. Originally approved in 2002. Last previous edition approved in 20082012 asD6845 02 (2008).D6845 12. DOI: 10.1520/D6845-12.10.1520/D6845-18.2 For referencedAST
13、M standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Aerosol OT is a registered trademark of the American Cyanamid Co., Process Che
14、micals Dept., Wayne, NM 07470.This document is not an ASTM standard and is intended only to provide the user of an ASTM 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 recommend
15、s that users consult prior editions as appropriate. In all cases only the current versionof the standard as published 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 States15.3 Magnetic Spinb
16、ars,4chemically resistant covered (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 cm3 Berzelius beakers, glass vials, or other glass vessels.5.4 Glass Funnel, small.5.5 Glass Vials, with plastic screw ca
17、ps, 28 mm in outside diameter, about 40 cm3 capacity.5.6 Buret, 50 cm3, 0.1 cm3 divisions, Class A, preferably of automatic refilling and zeroing type (see Note 1) with reagentreservoir.NOTE 1Automatic burets are usually not certified to ClassAtolerance. Such burets should be checked for accuracy, a
18、nd if in error by more than 0.05cm3 at any point, a calibration curve should 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,5
19、50 cm3, attached to a suitable reservoir for CTAB solution.5.8 Pipet, 10 cm3, Class A.5.9 Erlenmeyer Flasks, or beakers, 50 or 100 cm3.5.10 Dropping Bottle, 60 cm3 amber.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
20、ing 105 6 5C.5.13 Magnetic Stirrer.5.14 Containers, suitable for preparation and storage of reagent solutions.5.15 Automatic Titration Equipment with 550 nm Photoprobe,6with instruction manual.5.16 Beakers, 100 cm3 Berzelius, tall form (one furnished with automatic titration equipment).5.17 Thermome
21、ter, to measure temperature in a range from 20 to 40C.5.18 Polyethylene Tubing (do not use vinyl tubing).5.19 Wire mesh sieve, 75 m (200 mesh).NOTE 2All apparatus must be kept chemically clean. Contamination of equipment, water supply, or chemicals by ionic surfactants must beparticularly avoided.6.
22、 Reagents6.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.7 Other grades
23、may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening 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 Speci
24、fication D1193.6.3 Sodium Hydroxide Solution (1M)Dissolve 40.0 g NaOH in a 1 dm3 flask containing 0.5 dm3 reagent water. Afterdissolution 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) an
25、d 36.85 cm3 of sodium hydroxide (NaOH) solution in a 1 dm3 flask containing 0.5 dm3 reagent water.After dissolution fill to mark. Verify that the pH of the solution is 9.6 6 0.1.6.5 CTAB Standard SolutionDissolve 5.55.50 g of reagent-grade CTAB8 in a 1 dm3 flask containing 3500.350 dm3 of buffersolu
26、tion and 500 dm3 water. After dissolution fill to mark. Homogenize on a magnetic stirrer for 10 h. Allow to stand 24 h beforeuse. Verify that the pH of 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 HCl solution (too high). (Warning Stor
27、age of the solution below 22C will result in slow crystallization of the CTAB.)6.6 Aerosol OT9 Solution 100 % Grade (approximately 0.00389 M)Dissolve 1.73 g/dm3 of Aerosol OT solution (100 %solids) in 500 cm3 distilled or deionized water. Stir vigorously with a magnetic stirrer for 10 h.Allow to sta
28、nd an additional twelvedays before standardization and use.The solution should be capped tightly and stored in a cool place. (Once opened, 100 %AerosolOT should be stored in a desiccator.)4 Examples of suitable spinbars are Catalog No. 9235-U7, A. H. Thomas Co., Philadelphia, PA 19105, or Catalog No
29、. S-76497-30, Sargent Welch Scientific Co., Skokie,IL 60076.5 This test is based on the use of the Universal Repipet, a registered trademark of Labindustries, 1802 Second St., Berkeley, CA 94710.6 This test is based on the use of two sources of automatic titration equipment: (1) Mettler Memotitrator
30、 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 Instruments, has beenfound to be an acceptable automatic means of detecting the titration end po
31、int. This piece of equipment may be integrated with the Brinkman Dosimat 665 Buret.7 Reagent Chemicals, American Chemical Society Specifications , Am. Chemical Soc., Washington, DC. For suggestions on the testing of reagents not listed by theAmerican Chemical Society, see Reagent Chemicals and Stand
32、ards, by Joseph Rosin, D. Van Nostrand Co., Inc., New York, NY, and the United States Pharmacopeia.8 Available from J. T. Baker Chemical Co., 222 Red School Lane, Phillipsburgh, NJ 08865, Catalog No. 7N121.9 Available from American Cyanamid Co., Process Chemicals Dept., Wayne, NM 07470. Also availab
33、le as Catalog No. A-349 from Fisher Scientific Co.D6845 1826.7 Distilled or Deionized Water.6.8 Octylphenoxy Polyethoxyethanol (Triton X-10010) Solution (0.15 %)Dissolve 1.5 g in 1 dm3 of Triton X-100 (100 %liquid) in distilled or deionized water by swirling vigorously with a magnetic stirrer until
34、a homogeneous solution is obtained.7. Sampling7.1 No separate practice for sampling silicas is available. However, samples may be taken in accordance with Practices D1799or D1900.8. Standardization of Reagents8.1 Duplicate blanks are determined and averaged.8.2 Pipet 105 cm3 of CTAB solution into a
35、beaker.8.3 Add 50 cm3 of 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 of silica at 105C for 2 h an
36、d 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 Grind an appropriate quantity of silica sample in a laboratory grinder for 60 s.9.3 Pass ground sampl
37、e through a wire mesh sieve 75 m (200 mesh). This can be accomplished manually or mechanically.Discard fraction retained on sieve. The fraction 75 m (200 mesh) is used for the determination of the CTAB surface area.9.4 Weigh, to 0.1 mg, a suitable sample of the dried silica into a glass vial and rec
38、ord the mass as W.Appropriate sample massesmay be selected as follows:Approximate SurfaceArea, m2/g (SA)Sample Mass,gSA # 90 0.60090 SA # 120 0.500120 SA # 175 0.400175 SA # 220 0.300220 SA 0.200An appropriate sample mass may also be taken as Vo53/Sest in g, where Sest is some estimate of the expect
39、ed CTAB surface area.9.5 Insert a magnetic spinbar into the vial. Add 30.0 cm3 of CTAB solution from the dispensing pipet or buret taking care toprevent foaming of the solution. Cap the vial.9.6 Place the vial on a magnetic stirrer. Adjust the stirrer to give a vigorous stirring by the spinbar to pr
40、oduce a deep votexwithout foaming. Stir for 40 min.9.7 Immediately after completion of the stirring, decant the suspension into a centrifuge tube.9.8 Separate the silica from the suspension by centrifuging for 20 min at 4000 rpms.9.9 Pipet a 10.00 cm3 aliquot of the CTAB solution from the centrifuge
41、 tube into a 100 cm3 beaker 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. Add 50 cm3 of distilled or deionized water as under 8.3.9.10 Titration (Automatic):9.10.1 Prepare the automatic titrat
42、ion apparatus according to the instructions furnished with it.Ascertain 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 reserv
43、oir cap to admit air as liquid flows out. Adjust the titrantflow rate to 10 cm3/min.9.10.2 Lower the 550 nm photo probe into the solution.9.10.3 Lower the titrant delivery assembly so that the delivery needle is just below the surface of the liquid and open the titrantstopcock.9.10.4 Set the pump co
44、ntrol switch to the “titrate” position and press the “start” button.9.10.5 After the system stops record the amount of OT dispensed.9.10.6 Raise the titrant delivery tube clear of the beaker.9.10.7 Move the pump control to “flush” and allow a few drops of titrant to clear the needle. After the pump
45、stops, close thestopcock and remove the needle from the beaker. Wipe the needle with a clean tissue (do not use solvent).9.10.8 Remove and rinse the photoprobe with distilled water.D6845 1839.10.9 The unit is now ready for another sample.10. Calculation10.1 Calculate the CTAB surface area to the nea
46、rest 0.1 103 m2/g as follows:S 52V02V! 34774/V03W1002Vol!# (1)where:S = CTAB surface area of dried silica, 103 m2 /g,V0 = volume of OT required to titrate 5 cm3 of CTAB (Blank),V = aerosol OT solution required for the 10 cm3 sample,W = sample mass, g, andVol = volatile matter of silica, %.11. Report
47、11.1 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 0.1 103 m2/g.12. Precision and Bias12.1 The precision of this test method is based on an interlaboratory study conducted in 2010
48、. Nine laboratories tested two typesof silica samples. Every “test result” represents an individual determination. Each laboratory was instructed to report four replicatetest results for each material. Precision and bias statements according to Practice E691D4483 was followed for the design andanaly
49、sis of the data.have not been generated after including the sieve step, but will be available within five years of publicationof the test method.12.1.1 Repeatability Limit (r)Two test results obtained within 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 laboratory.12.1.1.1 Repeatability limits are listed
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