1、Designation: D6556 10D6556 14Standard Test Method forCarbon BlackTotal and External Surface Area by NitrogenAdsorption1This standard is issued under the fixed designation D6556; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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 determination of the total surface area by the Brunauer, Emmett, and Teller (B.E.T.
3、 NSA) theoryof multilayer gas adsorption behavior using multipoint determinations and the external surface area based on the statisticalthickness surface area method.1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.3 Thi
4、s 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 health practices and determine the applicability of regulatorylimitations prior to use. (The minimum safety equ
5、ipment should include protective gloves, sturdy eye and face protection).2. Referenced Documents2.1 ASTM Standards:2D1799 Practice for Carbon BlackSampling Packaged ShipmentsD1900 Practice for Carbon BlackSampling Bulk ShipmentsD3765 Test Method for Carbon BlackCTAB (Cetyltrimethylammonium Bromide)
6、Surface Area (Withdrawn 2007)3D4483 Practice for Evaluating Precision for Test Method Standards in the Rubber and Carbon Black Manufacturing Industries3. Summary of Test Method3.1 The total and external surface areas are measured by evaluating the amount of nitrogen adsorbed, at liquid nitrogentempe
7、rature, by a carbon black at several partial pressures of nitrogen. The adsorption data is used to calculate the NSAand STSAvalues.4. Significance and Use4.1 This test method is used to measure the total and external surface area of carbon blacks based on multipoint nitrogenadsorption. The NSA measu
8、rement is based on the B.E.T. theory and it includes the total surface area, inclusive of micropores,pore diameters less than 2 nm (20 ). The external surface area, based on the statistical thickness method (STSA), is defined asthe specific surface area that is accessible to rubber.4.2 CTAB SurfaceA
9、rea (formerly Test Method D3765) has been withdrawn. The CTAB value may be estimated from the STSAvalue using Eq 1. The equation is based on a linear regression of the STSA and CTAB measured values of the SRB 5 standards.CTAB5STSA*1.017012.6434 (1)5. Apparatus5.1 Multipoint Static-Volumetric Gas Ads
10、orption Apparatus, with Dewar flasks and all other accessories required for operation.5.2 Sample Cells, that when attached to the adsorption apparatus, will maintain isolation of the sample from the atmosphereequivalent to a helium leak rate of 1 L)Fill and cover the Dewar for a minimum of 16 h prio
11、r to use, unless continuous Po measurementsare employed. For continuous Po, use a 2-h Dewar equilibration. Once equilibration is reached, a large Dewar can maintain thisequilibration for several days if kept filled and covered. The cleaning frequency is left to the discretion of the operator, but is
12、 notto exceed once per week.9.3 Following is a list of Po measurement options:9.3.1 Continuous Po (measurement at each relative pressure point)This method is considered the best practice; however, itgenerally increases analysis time.9.3.2 Single Po Per AnalysisAlthough this value can be measured bef
13、ore, during, or after the run, a Po value measured at theend of the analysis is preferred, since STSA is calculated from the last data points acquired and is significantly influenced by Povalues. This method requires that a Po value be determined prior to initiating any measurements to ensure equili
14、brium of the Dewaras described in 9.4. Subsequently, a new Po value is measured for each run, which is used for calculating NSA/STSA values.9.3.3 Daily PoThis method is used when evidence of a stable Dewar is present and no changes in atmospheric pressure greaterthan 0.13 kPa (1 mm Hg) occur.9.3.4 C
15、alculated PoThis method calculates a Po value by measuring atmospheric pressure and adding a value between 1.3 and2.6 kPa (10 and 20 mm Hg). The operator is responsible for determining the constant used in their laboratory; however, 2.0 kPa(15 mm Hg) is most commonly used.9.4 With the exception of c
16、ontinuous Po measurements, it is recommended that the Po value be determined prior to initiatingNSA/STSA analyses. A Po value of 1.3 to 2.6 kPa (10 to 20 mm Hg) above atmospheric pressure and two consecutive Po valuesthat differ by no more that 0.13 kPa (1 mm Hg) over a 10-min time period are indica
17、tions of a stable Dewar. Experience will teachthe operator about expected differences in Po and atmospheric pressure in their laboratory.NOTE 4A minimum wait time of 10 min is recommended between Po measurements, as immersing the Po cell into the LN2 disrupts the temperatureequilibration. Po measure
18、ments taken at short intervals will result in erroneously high and unstable values.9.5 Determine the free space of the sample cell by measurement with helium or by calculation using an assumed carbon blackdensity of 1.9 g/cm3.9.6 Obtain a minimum of five data points evenly spaced in the 0.1 to 0.5 r
19、elative pressure (P/Po) range. For some tread carbonblacks, particularly N100 and N200 series, it is necessary to measure two additional data points, 0.05 and 0.075, in order to increasethe accuracy of the NSAmeasurement.Adata point consists of the relative pressure of equilibrium and the total amou
20、nt of nitrogengas adsorbed by the sample at that relative pressure.9.7 Determine the mass of the cell with dry sample to the nearest 0.1 mg. This may be done before or after measuring nitrogenadsorption. Avoid inconsistent use of helium, as a buoyancy error of 1 mg/cm3 of cell volume can occur. As a
21、n alternative, thecarbon black mass may be determined directly by pouring it from the sample cell into a tared weighing pan, taking care to removeall of the carbon black.10. Calculation10.1 Most automated instruments will perform the following computations at the completion of the analysis. The user
22、 mustverify that the internal computations conform to the following method.10.2 Sample Mass:sample mass dried!5mass of cell1sample!2mass 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 gram of sample to the nearest 0
23、.0001 cm3/g as follows:Va 5 Volume of Nitrogen for each dosing in cm3sample mass in g (3)10.4 Nitrogen Surface Area:10.4.1 Determine the nitrogen surface area (NSA) using a B.E.T. plot from the Brunauer, Emmett, and Teller4 equation asfollows:PVa Po 2P! 51VmC1C 21VmC 3PPo (4)4 Brunuaer, Emmett, and
24、Teller, Journal of the American Chemical Society, Vol. 60 , 1938, p. 309.D6556 143where:P = manometer pressure in kPa,Po = saturation vapor pressure of nitrogen in kPa,Vm = volume of nitrogen per gram that covers one monomolecular layer in standard cm3/g, andC = B.E.T. constant. Its numerical value
25、depends on the heat of adsorption of the monomolecular layer.10.4.2 Plot P/Po on the X-axis versus PVa Po2P!on the Y-axis, for data sets having P/Po in the range of 0.05 to 0.30 (linearregion of B.E.T. equation).10.4.3 The data points (three or more) that give the best straight line are used to calc
26、ulate the slope and y-intercept. The slopeand y-intercept are used to calculate the surface area. For examples of how to select the proper relative pressure range, see Table1.10.4.4 As an alternative, the interpretation of the proper relative pressure can generally be simplified by specifying the fo
27、llowingpressure 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 operator to assure that these guidelines are appropriate for their samples.10.4.5 A B.E.T. plot that yields a negative y
28、-intercept could be indicative of the presence of micropores (2 nm diameter), butother factors can produce a negative y-intercept. The surface area is calculated from three or more points within the pressure rangethat yields the highest correlation coefficient and a positive y-intercept.10.4.6 Calcu
29、late the nitrogen surface area to the nearest 0.1 m2/g as follows:Surface area m2 /g!5Vm34.35 (5)where:Vm = 1B1MB = Y-axis intercept, 6105,M = slope of the straight line, 6105, andTABLE 1 Example of NSA Data AnalysisN121ARaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNS
30、A,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 0.999935 122.8N326BRaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNS
31、A,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 0.999979 76.6N683BRaw Data CalculationP/PoVol. Ads.,cm3/gRel. Press.RangeCorrelationCoefficientNSA,m2
32、/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 38.4A The most accurate NSA is measured between 0.05 and 0.20 relative pressure.B The most accurate
33、 NSA is measured between 0.05 and 0.30 relative pressure.D6556 1444.35 = area occupied by 1 cm3 of nitrogen =6.0231023!16.2310220!224006.02 1023 = Avogadros number,16.2 1020 = area of nitrogen molecule in m2, and22400 = number of cm3 occupied by one mole of gas at STP.10.5 Statistical Thickness Surf
34、ace Area:10.5.1 Determine the STSA5 of the black using a plot of the volume of nitrogen gas adsorbed per gram of sample at STP (Va)versus the statistical layer thickness (t).10.5.2 Prepare the Va-t plot by plottingt (nm) on theX axis versusVa(dm3/kg at STP) on theYaxis, for data sets havingP/Poequal
35、ly spaced in the range of 0.2 to 0.5.where:t = statistical layer thickness of carbon black =0.088(P/Po)2 + 0.645 (P/Po) + 0.298NOTE 5The carbon black thickness model was developed using an N762 carbon black in the P/Po range of 0.2 to 0.5. T values calculated outsideof this range are invalid and wil
36、l result in erroneous STSA values.10.5.3 Determine the slope of the Va-t plot using standard linear regression.10.5.4 Calculate the STSA to the nearest 0.1 m2/g as follows:STSA5M 315.47 (6)where:M = slope of the Va-tplot, and15.47 = a constant for the conversion of nitrogen gas to liquid volume, and
37、 conversion of units to m2/g.10.5.5 STSA is based on a thickness model developed using an N762 carbon black. This carbon black was chosen because ofits low surface area and low structure level. This universal model does not perfectly apply to all carbon blacks; consequently, whileit is theoretically
38、 impossible for external surface area to be higher than total surface area, in practice there are instances whereSTSA is higher than NSA. For analyses that yield STSA values that are higher than NSA, the measured STSA value should bereported.11. Report11.1 Report the following information:11.1.1 Pro
39、per sample identification,11.1.2 Number of data points and relative pressures used to obtain both NSA and STSA,11.1.3 The sample mass to the nearest 0.1 mg, and11.1.4 The NSA or STSA, or both, of the sample reported to the nearest 0.1 m2/g.12. Precision and Bias12.1 These precision statements have b
40、een prepared in accordance with Practice D4483. Refer to this practice for terminologyand other statistical details.12.2 The precision results in this precision and bias section give an estimate of the precision of this test method with thematerials used in the particular interlaboratory program des
41、cribed below. The precision parameters should not be used foracceptance or rejection testing of any group of materials without documentation that they are applicable to those particularmaterials and the specific testing protocols of the test method. Any appropriate value may be used from Tables 2 an
42、d 3.12.3 Nitrogen Surface Area (NSA):12.3.1 A Type 1 interlaboratory precision program was conducted. Both repeatability and reproducibility represent short-term(daily) testing conditions. The testing was performed using two operators in each laboratory performing the test once on eachmaterial on ea
43、ch of two days (total of four tests). The number of participating laboratories is listed in Table 2.12.3.2 The results of the precision calculations for this test are given in Table 2. The materials are arranged in ascending “meanlevel” order.12.3.3 RepeatabilityThe pooled relative repeatability, (r
44、), of the NSA test has been established as 1.87 %. Any other valuein Table 2 may be used as an estimate of repeatability, as appropriate. The difference between two single test results (ordeterminations) found on identical test material under the repeatability conditions prescribed for this test wil
45、l exceed the5 Magee, R. W., Rubber Chemistry and Technology, Vol. 68, No. 4, 1995, p. 590.D6556 145repeatability on an average of not more than once in 20 cases in the normal and correct operation of the method. Two single testresults that differ by more than the appropriate value from Table 2 must
46、be suspected of being from different populations and someappropriate action taken.NOTE 6Appropriate action may be an investigation of the test method procedure or apparatus for faulty operation or the declaration of a significantdifference in the two materials, samples, and so forth, which generated
47、 the two test results.12.3.4 ReproducibilityThe pooled relative reproducibility, (R), of the NSA test has been established as 3.18 %. Any othervalue in Table 2 may be used as an estimate of reproducibility, as appropriate. The difference between two single and independenttest results found by two op
48、erators working under the prescribed reproducibility conditions in different laboratories on identicaltest material will exceed the reproducibility on an average of not more than once in 20 cases in the normal and correct operationof the method. Two single test results produced in different laborato
49、ries that differ by more than the appropriate value from Table2 must be suspected of being from different populations and some appropriate investigative or technical/commercial action taken.12.3.5 BiasIn test method terminology, bias is the difference between an average test value and the reference (true) testproperty value. Reference values do not exist for this test method since the value or level of the test property is exclusively definedby the test method. Bias, therefore, cannot be determined.12.4 Statistical Thickness Surface Are
