1、Designation: D 6556 09Standard Test Method forCarbon BlackTotal and External Surface Area by NitrogenAdsorption1This standard is issued under the fixed designation D 6556; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 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 determination of the totalsurface area by the Brunauer, Emmett, and Teller (B.E.T. NSA)th
3、eory of multilayer gas adsorption behavior using multipointdeterminations and the external surface area based on thestatistical thickness surface area method.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard
4、 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 applica-bility of regulatory limitations prior to use. (The minimumsafety equipment sh
5、ould include protective gloves, sturdy eyeand face protection).2. Referenced Documents2.1 ASTM Standards:2D 1799 Practice for Carbon BlackSampling PackagedShipmentsD 1900 Practice for Carbon BlackSampling Bulk Ship-mentsD 3765 Test Method for Carbon BlackCTAB (Cetyltrim-ethylammonium Bromide) Surfac
6、e Area3D 4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3. Summary of Test Method3.1 The total and external surface areas are measured byevaluating the amount of nitrogen adsorbed, at liquid nitrogentemperature, by a carbon black
7、 at several partial pressures ofnitrogen. The adsorption data is used to calculate the NSA andSTSA values.4. Significance and Use4.1 This test method is used to measure the total andexternal surface area of carbon blacks based on multipointnitrogen adsorption. The NSA measurement is based on theB.E.
8、T. theory and it includes the total surface area, inclusive ofmicropores, pore diameters less than 2 nm (20 ). The externalsurface area, based on the statistical thickness method (STSA),is defined as the specific surface area that is accessible torubber.4.2 CTAB Surface Area (formerly Test Method D
9、3765) hasbeen withdrawn. The CTAB value may be estimated from theSTSA value using Eq 1. The equation is based on a linearregression of the STSAand CTAB measured values of the SRB5 standards.CTAB 5 STSA * 1.0170 1 2.6434 (1)5. Apparatus5.1 Multipoint Static-Volumetric Gas Adsorption Apparatus,with De
10、war flasks and all other accessories required foroperation.5.2 Sample Cells, that when attached to the adsorptionapparatus, will maintain isolation of the sample from theatmosphere equivalent to a helium leak rate of 1 L)Fill and cover the Dewar for aminimum of 16 h prior to use, unless continuous P
11、omeasure-ments are employed. For continuous Po, use a 2-h Dewarequilibration. Once equilibration is reached, a large Dewar canmaintain this equilibration for several days if kept filled andcovered. The cleaning frequency is left to the discretion of theoperator, but is not to exceed once per week.9.
12、3 Following is a list of Pomeasurement options:9.3.1 Continuous Po(measurement at each relative pressurepoint)This method is considered the best practice; however,it generally increases analysis time.9.3.2 Single PoPer AnalysisAlthough this value can bemeasured before, during, or after the run, a Po
13、value measuredat the end of the analysis is preferred, since STSA is calculatedfrom the last data points acquired and is significantly influ-enced by Povalues. This method requires that a Povalue bedetermined prior to initiating any measurements to ensureequilibrium of the Dewar as described in 9.4.
14、 Subsequently, anew Povalue is measured for each run, which is used forcalculating NSA/STSA values.9.3.3 Daily PoThis method is used when evidence of astable Dewar is present and no changes in atmospheric pressuregreater than 0.13 kPa (1 mm Hg) occur.9.3.4 Calculated PoThis method calculates a Poval
15、ue bymeasuring atmospheric pressure and adding a value between1.3 and 2.6 kPa (10 and 20 mm Hg). The operator isresponsible for determining the constant used in their labora-tory; however, 2.0 kPa (15 mm Hg) is most commonly used.9.4 With the exception of continuous Pomeasurements, it isrecommended
16、that the Povalue be determined prior to initiat-ing NSA/STSAanalyses.APovalue of 1.3 to 2.6 kPa (10 to 20mm Hg) above atmospheric pressure and two consecutive Povalues that differ by no more that 0.13 kPa (1 mm Hg) over a10-min time period are indications of a stable Dewar. Experi-ence will teach th
17、e operator about expected differences in Poand atmospheric pressure in their laboratory.D6556092NOTE 2A minimum wait time of 10 min is recommended between Pomeasurements, as immersing the Pocell into the LN2 disrupts thetemperature equilibration. Pomeasurements taken at short intervals willresult in
18、 erroneously high and unstable values.9.5 Determine the free space of the sample cell by measure-ment with helium or by calculation using an assumed carbonblack density of 1.9 g/cm3.9.6 Obtain a minimum of five data points evenly spaced inthe 0.1 to 0.5 relative pressure (P/Po) range. For some tread
19、carbon blacks, particularly N100 and N200 series, it is neces-sary to measure two additional data points, 0.05 and 0.075, inorder to increase the accuracy of the NSAmeasurement.Adatapoint consists of the relative pressure of equilibrium and thetotal amount of nitrogen gas adsorbed by the sample at t
20、hatrelative pressure.9.7 Determine the mass of the cell with dry sample to thenearest 0.1 mg. This may be done before or after measuringnitrogen adsorption. Avoid inconsistent use of helium, as abuoyancy error of 1 mg/cm3of cell volume can occur. As analternative, the carbon black mass may be determ
21、ined directlyby pouring it from the sample cell into a tared weighing pan,taking care to remove all of the carbon black.10. Calculation10.1 Most automated instruments will perform the follow-ing computations at the completion of the analysis. The usermust verify that the internal computations confor
22、m to thefollowing method.10.2 Sample Mass:sample mass dried!5mass of cell 1 sample! mass of cell!(2)Record masses to nearest 0.1 mg.10.3 Volume of Nitrogen Adsorbed:10.3.1 Calculate total volume of nitrogen adsorbed per gramof sample to the nearest 0.0001 cm3/g as follows:Va5Volume of Nitrogen for e
23、ach dosing in cm3sample mass in g(3)10.4 Nitrogen Surface Area:10.4.1 Determine the nitrogen surface area (NSA) using aB.E.T. plot from the Brunauer, Emmett, and Teller4equation asfollows:PVaPoP!51VmC1C1VmC3PPo(4)where:P = manometer pressure in kPa,Po= saturation vapor pressure of nitrogen in kPa,Vm
24、= volume of nitrogen per gram that covers one mono-molecular layer in standard cm3/g, andC = B.E.T. constant. Its numerical value depends on theheat of adsorption of the monomolecular layer.10.4.2 Plot P/Poon the X-axis versusPVaPoP!on theY-axis, for data sets having P/Poin the range of 0.05 to 0.30
25、(linear region of B.E.T. equation).10.4.3 The data points (three or more) that give the beststraight line are used to calculate the slope and y-intercept. Theslope and y-intercept are used to calculate the surface area. Forexamples of how to select the proper relative pressure range,see Table 1.10.4
26、.4 As an alternative, the interpretation of the properrelative pressure can generally be simplified by specifying thefollowing pressure ranges for the various carbon black types:BET RangeN300 and Carcass Grades 0.10.3N100 and N200 0.050.2Carbon Blacks 130 m2/g 0.050.1It is the responsibility of the
27、operator to assure that theseguidelines are appropriate for their samples.10.4.5 A B.E.T. plot that yields a negative y-intercept couldbe indicative of the presence of micropores (2 nm diameter),but other factors can produce a negative y-intercept. Thesurface area is calculated from three or more po
28、ints within thepressure range that yields the highest correlation coefficientand a positive y-intercept.10.4.6 Calculate the nitrogen surface area to the nearest 0.1m2/g as follows:4Brunuaer, Emmett, and Teller, Journal of the American Chemical Society, Vol.60, 1938, p. 309.TABLE 1 Example of NSA Da
29、ta AnalysisN121ARaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNSA,m2/g0.0500 26.716 . . . . . . . . .0.1000 29.753 . . . . . . . . .0.1500 32.313 0.050.15 0.999981 123.90.2000 34.692 0.050.20 0.999992 124.00.2500 37.110 0.050.25 0.999990 123.60.3000 39.641 0.050.30 0.9
30、99935 122.8N326BRaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNSA,m2/g0.0500 16.675 . . . . . . . . .0.1000 18.318 . . . . . . . . .0.1500 19.859 0.050.15 0.999960 75.60.2000 21.426 0.050.20 0.999948 76.30.2500 23.035 0.050.25 0.999964 76.60.3000 24.751 0.050.30 0.9999
31、79 76.6N683BRaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNSA,m2/g0.0500 8.194 . . . . . . . . .0.1000 9.113 . . . . . . . . .0.1500 9.945 0.050.15 0.999939 38.20.2000 10.739 0.050.20 0.999950 38.50.2500 11.543 0.050.25 0.999972 38.60.3000 12.364 0.050.30 0.999973 38.4
32、AThe most accurate NSAis measured between 0.05 and 0.20 relative pressure.BThe most accurate NSAis measured between 0.05 and 0.30 relative pressure.D6556093Surface area m2/g!5Vm 3 4.35 (5)where:Vm =1B 1 MB = Y-axis intercept, 6105,M = slope of the straight line, 6105, and4.35 = area occupied by 1 cm
33、3of nitrogen =6.02 3 1023!16.2 3 1020!224006.02 3 1023= Avogadros number,16.2 3 1020= area of nitrogen molecule in m2, and22400 = number of cm3occupied by one mole ofgas at STP.10.5 Statistical Thickness Surface Area:10.5.1 Determine the STSA5of the black using a plot of thevolume of nitrogen gas ad
34、sorbed per gram of sample at STP(Va) versus the statistical layer thickness (t).10.5.2 Prepare the Va-t plot by plotting t (nm) on the X axisversus Va(dm3/kg at STP) on the Y axis, for data sets havingP/Poequally spaced in the range of 0.2 to 0.5.where:t = statistical layer thickness of carbon black
35、 =0.088(P/Po)2+ 0.645 (P/Po) + 0.29810.5.3 Determine the slope of the Va-t plot using standardlinear regression.10.5.4 Calculate the STSA to the nearest 0.1 m2/g asfollows:STSA 5 M 3 15.47 (6)where:M = slope of the Va-t plot, and15.47 = a constant for the conversion of nitrogen gas toliquid volume,
36、and conversion of units to m2/g.10.5.5 STSA is based on a thickness model developed usingan N762 carbon black. This carbon black was chosen becauseof its low surface area and low structure level. This universalmodel does not perfectly apply to all carbon blacks; conse-quently, while it is theoretica
37、lly impossible for external surfacearea to be higher than total surface area, in practice there areinstances where STSA is higher than NSA. For analyses thatyield STSA values that are higher than NSA, the measuredSTSA value should be reported.11. Report11.1 Report the following information:11.1.1 Pr
38、oper sample identification,11.1.2 Number of data points and relative pressures used toobtain both NSA and STSA,11.1.3 The sample mass to the nearest 0.1 mg, and11.1.4 The NSAor STSA, or both, of the sample reported tothe nearest 0.1 m2/g.12. Precision and Bias12.1 These precision statements have bee
39、n prepared inaccordance with Practice D 4483. Refer to this practice forterminology and other statistical details.12.2 The precision results in this precision and bias sectiongive an estimate of the precision of this test method with thematerials used in the particular interlaboratory program de-scr
40、ibed below. The precision parameters should not be used foracceptance or rejection testing of any group of materialswithout documentation that they are applicable to those par-ticular materials and the specific testing protocols of the testmethod. Any appropriate value may be used from Tables 2 and3
41、.12.3 Nitrogen Surface Area (NSA):12.3.1 A Type 1 interlaboratory precision program wasconducted. Both repeatability and reproducibility representshort-term (daily) testing conditions. The testing was per-formed using two operators in each laboratory performing thetest once on each material on each
42、of two days (total of fourtests). The number of participating laboratories is listed inTable 2.12.3.2 The results of the precision calculations for this testare given in Table 2. The materials are arranged in ascending“mean level” order.12.3.3 RepeatabilityThe pooled relative repeatability,(r), of t
43、he NSA test has been established as 1.87 %. Any othervalue in Table 2 may be used as an estimate of repeatability, asappropriate. The difference between two single test results (ordeterminations) found on identical test material under therepeatability conditions prescribed for this test will exceed
44、therepeatability on an average of not more than once in 20 casesin the normal and correct operation of the method. Two singletest results that differ by more than the appropriate value fromTable 2 must be suspected of being from different populationsand some appropriate action taken.NOTE 3Appropriat
45、e action may be an investigation of the test methodprocedure or apparatus for faulty operation or the declaration of asignificant difference in the two materials, samples, and so forth, whichgenerated the two test results.12.3.4 ReproducibilityThe pooled relative reproducibil-ity, (R), of the NSA te
46、st has been established as 3.18 %. Anyother value in Table 2 may be used as an estimate ofreproducibility, as appropriate. The difference between twosingle and independent test results found by two operatorsworking under the prescribed reproducibility conditions in5Magee, R. W., Rubber Chemistry and
47、 Technology, Vol. 68, No. 4, 1995, p.590.TABLE 2 Precision Parameters for Test Method D 6556, CarbonBlackNSA (Type 1 Precision)Units 103m2/kg (m2/g)MaterialNumber ofLaboratoriesMeanLevel Sr (r) SR (R)SRB D6 (N762) 19 30.6 0.25 2.33 0.41 3.82SRB F6 (N683) 19 35.3 0.47 3.77 0.60 4.83SRB E6 (N660) 19 3
48、6.0 0.40 3.16 0.48 3.77SRB C6 (N326) 18 78.3 0.40 1.44 0.78 2.82SRB B6 (N220) 19 110.0 0.53 1.37 0.94 2.42SRB A6 (N134) 19 143.9 0.70 1.37 1.30 2.56Average 72.4Pooled Values 0.48 1.87 0.81 3.18D6556094different laboratories on identical test material will exceed thereproducibility on an average of n
49、ot more than once in 20 casesin the normal and correct operation of the method. Two singletest results produced in different laboratories that differ bymore than the appropriate value from Table 2 must besuspected of being from different populations and some appro-priate investigative or technical/commercial action taken.12.3.5 BiasIn test method terminology, bias is the differ-ence between an average test value and the reference (true) testproperty value. Reference values do not exist for this testmethod since the value or level of the te
