炭黑材料中比表面积检测方案(比表面)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards， Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. 4ly D6556-17 Designation： D6556-17 INTERNATIONAL Standard Test Method forCarbon Black—Total and External Surface Area by NitrogenAdsorption' This 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 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. Scope 1.1 This test method covers the determination of the totalsurface area by the Brunauer， Emmett， and Teller (B.E.T. NSA)theory 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 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， health， and environmental practices and deter-mine the applicability of regulatory limitations prior to use.(The minimum safety equipment should include protectivegloves， sturdy eye and face protection). 1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards， Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee. 2. Referenced Documents 2.1 ASTM Standards： D1799 Practice for Carbon Black—Sampling PackagedShipments D1900 Practice for Carbon Black—Sampling Bulk Ship-ments ( T h is t e s t m et h od is u nder the jurisdi c tion o f ASTM Co m mittee D 2 4 o n Carb o n B lac k a nd i s t he dir e ct r e sponsibili t y o f Subcommitte e D24.21 on Carbon B lac kS urface Area a nd Rel a ted Propertie s . ) ( Current e dition a p proved Oc t . 1 ， 20 17. Published Nove m ber 2017. Origi n al l y a pproved i n 2 00 0 . L a st previous edition approved in 2016 as D6556- 16 . D O I：10.15 2 0/D6 5 56-17. ) For referenced ASTM standards， visit the ASTM website， www.astm.org， orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information， refer to the standard’s Document Summary page onthe ASTM website. 3. Summary of Test Method 3.1 The total and external surface areas are measured byevaluating the amount of nitrogen adsorbed， at liquid nitrogentemperature， by a carbon black at several partial pressures ofnitrogen. The adsorption data is used to calculate the NSA andSTSA values. 4. Significance and Use 4.1 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.T. theory and it includes the total surface area， inclusive ofmicropores， pore diameters less than 2 nm (20 A). 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 D3765) hasbeen withdrawn. The CTAB value may be estimated from theSTSA value using Eq 1. The equation is based on a linearregression of the STSA and CTAB measured values of the SRB5 standards. 5. Apparatus 5.1 Multipoint Static-Volumetric Gas Adsorption Apparatus，with Dewar 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 <10-5cm’/min，per atmosphere of pressure difference. ( T he l a st a pp roved v e rs i on of t hi s hi s t orical s ta n d ard is r e fer e nced onw w w . astm.o r g. ) 5.3 Balance， Analytical， with 0.1 mg sensitivity. 5.4 Heating Mantle or Equivalent， capable of maintaining atemperature of 300 ±10°C. 5.5 Oven， Gravity Convection， capable of maintaining atemperature of 125 ±10C. 6. Reagents 6.1 Liquid Nitrogen， 98 % or higher purity. 6.2 Ultra-High Purity Nitrogen Gas， cylinder or othersource of prepurified nitrogen gas. 6.3 Ultra-High Purity Helium Gas， cylinder or other sourceof prepurified helium gas. 7. Sampling 7.1 Samples may be taken in accordance with PracticesD1799 and D1900. 8. Sample Preparation Procedure 8.1 Dry a portion of carbon black at 125°C for 1 h. If thecarbon black is known to be substantially free of moisture， orsubsequent preparation steps are known to be adequate formoisture removal， then this step may be omitted. 8.2 Condition an empty sample cell for a minimum of 10min at the same conditions intended for degassing the sample.Weigh the empty sample cell to the nearest 0.1 mg and recordthe mass. 8.3 Weigh approximately 0.4 g of the carbon black into thesample cell. NoTE 1-For carbon black powder samples， add enough carbon blackto give a depth of approximately 2 in. in straight wall sample tubes， orapproximately 0.4 g for bulb-type sample cells. 8.4 Flow Degassing： 8.4.1 Open the gas control valve and insert the delivery tubeinto the sample tube， and allow purging with either helium ornitrogen for a minimum of 1 min. 8.4.2 Place a heating mantle or other source of heat aroundthe sample cell and degas the sample at 300 ±10℃ for V2 hor longer to ensure that all traces of moisture condensing in thetop of the tube are absent. The minimum degassing time thatgives a stable surface area (that is， a surface area that does notincrease with additional degassing) may be used for degassing. NoTE 2—For carbon blacks at their moisture pickup equilibrium， likestandard reference blacks， longer degassing times likely will be requiredin order to achieve stable results. It has been found that for SRB B8 andSRB C8， it is necessary to extend the degassing time to at least 60 min inorder to reliably obtain the target NSA and STSA values. This may be truefor other high structure and high porosity carbon blacks. 8.4.3 Once thettypical degassingtimeshave beendetermined， future samples can be degassed on the basis oftime alone， if desired， allowing a reasonable margin of excesstime. Some samples will be found to require less than V h，especially if moisture exposure has been minimal. In thesecases， the minimum time that gives a stable surface area maybe used for degassing. 8.4.4 After degassing， the sample tube may be moveddirectly to the analyzer. Otherwise， remove the sample tube from the heat source and continue the flow of purging gas untilit is ready for analysis. 8.4.5 Go directly to Section 9 and continue the remainingsteps of the procedure. 8.5 Vacuum Degassing： 8.5.1 With the apparatus at atmospheric pressure， place thesample cell containing the carbon black onto the degassingapparatus. 8.5.2 Begin the degassing procedure as appropriate for theapparatus. 8.5.3 Place a heating mantle or other source of heat aroundthe sample cell and degas the sample at 300 ±10°℃ for V2 hor longer as required to obtain and hold a pressure less than 1.4Pa (10 um Hg). NoTE 3-Attention! One-half hour vacuum degassing may be inad-equate for some grades and may result in statistically different results toflow degassing. 8.5.4 Once the typical degassing times have beendetermined， future samples can be degassed on the basis oftime alone， if desired， allowing a reasonable margin of excesstime. Some samples will be found to require less than V h，especially if moisture exposure has been minimal. In thesecases， the minimum time that gives a stable surface area maybe used for degassing (see Note 2). 8.5.5 Go directly to Section 9 and continue the remainingsteps of the procedure. 9.Measurement Procedure 9.1 Refer to the user’s manual or specific instructions for themultipoint gas adsorption analyzer to be used， and becomethoroughly familiar with the procedures. Ther)ce(e are numerousinstruments available that offer a variety of saturation vaporpressure (P) measurement options and Dewar sizes. 9.2 Fill the Dewar with liquid nitrogen (LN2) and allow it toreach temperature equilibrium. The Dewar should be refilledapproximately once per hour or between each analysis. Thetime required to reach equilibrium is dependent upon Dewarsize and quality. 9.2.1 Small Dewar (<1 L)-Fill and cover the Dewar for aminimum of 2 h prior to use. The Dewar should be cleaned anddried at the end of each day. 9.2.2 Large Dewar (>1L)-Fill and cover the Dewar for aminimum of 16 h prior to use， unless continuous P measure-ments are employed. For continuous P， 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. 9.3 Following is a list of P， measurement options： 9.3.1 Continuous P，(measurement at each relative pressurepoint)-This method is considered the best practice. Whenavailable with the instrument and software package， it isrecommended to use this option. 9.3.2 Single P。 Per Analysis-Although this value can bemeasured before， during， or after the run， a P， value measuredat the end of the analysis is preferred， since STSA is calculated TABLE 1 Example of NSA Data Analysis N121A Raw Data Calculation Vol. Ads.， Rel. Press. Correlation NSA， P/Po cm/g Range Coefficient m²/g 0.0500 26.716 ... ... ... 0.1000 29.753 ... ... 0.1500 32.313 0.05-0.15 0.999981 123.9 0.2000 34.692 0.05-0.20 0.999992 124.0 0.2500 37.110 0.05-0.25 0.999990 123.6 0.3000 39.641 0.05-0.30 0.999935 122.8 N326B Raw Data Calculation Vol. Ads.. Rel. Press. Correlation NSA. P/Po cm/g Range Coefficient m2/g 0.0500 16.675 ... ... ... 0.1000 18.318 ... ... 0.1500 19.859 0.05-0.15 0.999960 75.6 0.2000 21.426 0.05-0.20 0.999948 76.3 0.2500 23.035 0.05-0.25 0.999964 76.6 0.3000 24.751 0.05-0.30 0.999979 76.6 N683 Calculation Raw Data Vol. Ads.， Rel. Press. Correlation NSA. P/Po cm/g Range Coefficient m²/g 0.0500 8.194 ... ... ... 0.1000 9.113 ... ... ... 0.1500 9.945 0.05-0.15 0.999939 38.2 0.05-0.20 0.999950 38.5 0.05-0.30 0.999973 38.4 The most accurate NSA is measured between 0.05 and 0.20 relative pressure.The most accurate NSA is measured between 0.05 and 0.30 relative pressure. from the last data points acquired and is significantly influ-enced by P，values. This method requires that a P。 value bedetermined prior to initiating any measurements to ensureequilibrium of the Dewar as described in 9.4. Subsequently， anew P. value is measured for each run， which is used forcalculating NSA/STSA values. 9.3.3 Daily P.-This 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 P，-This method calculates a P， value 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 P， measurements， it isrecommended that the P value be determined prior to initiat-ing NSA/STSA analyses. A P， value of 1.3 to 2.6 kPa (10 to 20mm Hg) above atmospheric pressure and two consecutive P，values 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 the operator about expected differences in P，and atmospheric pressure in their laboratory. NoTE 4—A minimum wait time of 10 min is recommended between Pmeasurements， as immersing the P， cell into the LN2 disrupts thetemperature equilibration. P，measurements taken at short intervals willresult in 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/cm. 9.6 Obtain a minimum of five data points evenly spaced inthe 0.1 to 0.5 relative pressure (P/P，) range. For some treadcarbon 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 NSA measurement. A datapoint consists of the relative pressure of equilibrium and thetotal amount of nitrogen gas adsorbed by the sample at thatrelative 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/cm’ of cell volume can occur. As analternative， the carbon black mass may be determined directlyby pouring it from the sample cell into a tared weighing pan，taking care to remove all of the carbon black. 10. Calculation 10.1 Most automated instruments will perform the follow-ing computations at the completion of the analysis. The usermust verify that the internal computations conform to thefollowing method. 10.2 Sample Mass： sample mass (dried)= (mass of cell+ sample) - (mass ofcell) (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 cm /g as follows： 10.4 Nitrogen Surface Area： 10.4.1 Determine the nitrogen surface area (NSA) using aB.E.T. plot from the Brunauer， Emmett， and Tellert equation asfollows： where： P= manometer pressure in kPa，P = saturation vapor pressure of nitrogen in kPa， = volume of nitrogen per gram that covers one mono-molecular layer in standard cm/g， and C =： B.E.T. constant. Its numerical value depends on theheat of adsorption of the monomolecular layer. P10.4.2 Plot P/P， on the X-axis versus.ayY-axis， for data sets having P/P， in the range of 0.05 to 0.30(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. Number of Labs (M/H/L) SRB8 Material D6556 D6556 Grade Producer Test Period NSA STSA SRB-8A N326 Continental March 2008 58 (0/1/0) 54 (1/2/0) SRB-8A2 N326 Continental March 2013 67 (1/2/0) 63 (1/2/0) SRB-8B N134 Cabot June 2009 65 (0/3/1) 62(2/2/2) SRB-8B2 N134 Cabot March/April 2014 11 (1/1/0) 15 (1/1/0) SRB-8C HS Tread Columbian September 2010 63(1/2/0) 58 (2/3/0) SRB-8D LS Carcass Cabot March 2009 64 (1/2/2) 60(1/2/0) SRB-8E N660 Orion September 2008 54 (1/1/1) 51 (1/1/0) SRB-8F N683 Orion March 2010 67(2/2/0) 64(1/1/0) SRB-8F2 N683 Orion March 2015 30 (0/1/0) 44 (2/1/0) SRB-8GA N990 Cancarb Last half of 1996 N/A N/A ^SRB-8G was produced and approved in the last half of 1996 as SRB-5G and has continued to be included in the current SRB sets since that time. At the time it wasproduced and approved it was D24's practice to only publish the within-laboratory standard deviation， Sr， and associated limits. The between-laboratory standard deviation，SR， was never published and since the data is no longer available it is not possible to calculate or publish the SR values and corresponding limits. The SRB G materialwas only tested for NSA， STSA， and OAN per the test method version available in 1996. 10.4.4 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 Range It is the responsibility of the 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 points within thepressure range that yields the highest correlation coefficientand a positive y-intercept. 10.4.6 Calculate the nitrogen surface area to the nearest 0.1m /g as follows： where： (6.02×1023)(16.2×10-20) 22400 6.02×1023 =Avogadro’s number， 16.2×10-20 =aarea of nitrogen molecule in m ， and22400 = rnumber ofcm’occupied by one mole of gasat STP. 10.5 Statistical Thickness Surface Area： 10.5.1 Determine the STSA’ of the black using a plot of thevolume of nitrogen gas adsorbed per gram of sample at STP(V) versus the statistical layer thickness (t). 10.5.2 Prepare the V-t plot by plotting t (nm) on the X axisversus V (dm /kg at STP) on the Y axis， for data sets havingP/P，equally spaced in the range of 0.2 to 0.5. where： t = statistical layer thickness of carbon black =0.088(P/P，)+ 0.645 (P/P ，) + 0.298 NoTE 5-The carbon black thickness model was developed using anN762 carbon black in the P/Po range of 0.2 to 0.5. T values calculatedoutside of this range are invalid and will result in erroneous STSA values. 10.5.3 Determine the slope of the V-t plot using standardlinear regression. 10.5.4 Calculate the STSA to the nearest 0.1 m²/g asfollows： where： M slope of the V-t plot， and 15.47 a constant for the conversion of nitrogen gas toliquid volume， 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；consequently， while it is theoretically impossible for externalsurface area to be higher than total surface area， in practicethere are instances where STSA is higher than NSA. Foranalyses that yield STSA values that are higher than NSA， themeasured STSA value should be reported. 11. Report 11.1 Report the following information： 11.1.1 Proper 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， and 11.1.4 The NSA or STSA， or both， of the sample reported tothe nearest 0.1 m/g. 12. Precision and Bias 12.1 These precision statements have been prepared inaccordance with Practice D4483. Refer to this practice forterminology and other statistical details. 12.2 An Interlaboratory precision program (ITP) informa-tion was conducted as detailed in Table 2. Both repeatability and reproducibility represent short-term (daily) testing condi-tions. The testing was performed using two operators in eachlaboratory performing the test once on each of two days (totalof four tests). A test result is the value obtained from a singledetermination. Acceptable difference values were not mea-sured. The between operator component of variation is in-cluded in the calculated values for r and R. 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 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 3. The materials are arranged in ascending“mean level”order. 12.3.3 Repeatability-The pooled relative repeatability，(r)，of the NSA test has been established as 1.1 %. Any other valuein Table 3 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 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 3 must be suspected of being from different populationsand some appropriate action taken. NoTE 6—Appropriate 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 Reproducibility-The pooled relativereproducibility， (R)， of the NSA test has been established as 2.9%. Any other value in Table 3 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 indifferent laboratories on identical test material will exceed thereproducibility on an average of not more than once in 20 casesin the normal and correct operation of the method. Two singletest results produced in different laboratories that differ by TABLE 3 Precision Parameters for Test Method D6556，NSAMethod (Type 1 Precision)^ Units 10°m2/kg(m²/g) Material Mean Level Sr r (r) SR R (R) SRB-8B 142.0 0.47 1.34 0.9 1.44 4.06 2.9 SRB-8B2 138.0 0.31 0.87 0.6 0.79 2.24 1.6 SRB-8C 126.4 0.44 1.25 1.0 1.07 3.02 2.4 SRB-8A 76.5 0.33 0.94 1.2 0.84 2.38 3.1 SRB-8A2 75.9 0.29 0.81 1.1 0.70 1.98 2.6 SRB-8E 36.7 0.23 0.65 1.8 0.53 1.49 4.1 SRB-8F 36.7 0.21 0.58 1.6 0.38 1.09 3.0 SRB-8D 21.6 0.18 0.52 2.4 0.30 0.85 3.9 Average 81.7 Pooled Values 0.32 0.91 1.1 0.83 2.35 2.9 A The preferred precision values are shown in bold text. more than the appropriate value from Table 3 must besuspected of being from different populations and some appro-priate investigative or technical/commercial action taken. 12.3.5 Bias-In 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 test property isexclusively defined by the test method. Bias， therefore， cannotbe determined. 12.4 Statistical Thickness Surface Area (STSA)： 12.4.1 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 oftwo days (total of fourtests). The number of participating laboratories is listed inTable 2. 12.4.2 The results of the precision calculations for this testare given in Table 4. The materials are arranged in ascending“mean level”order. 12.4.3 Repeatability-The pooled relative repeatability，(r)，of the STSA test has been established as 1.7 %.Any other valuein Table 4 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 therepeatability on an average ofnot 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 4 must be suspected of being from different populationsand some appropriate action taken. NoTE 7-Appropriate 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. 12.4.4 Reproducibility-The pooled relativereproducibility， (R)， of the STSA test has been established as4.3 %. Any other value in Table 4 may be used as an estimateof reproducibility， as appropriate. The difference between twosingle and independent test results found by two operatorsworking under the prescribed reproducibility conditions indifferent laboratories on identical test material will exceed thereproducibility on an average of not more than once in 20 cases TABLE 4 Precision Parameters for Test Method D6556， STSA Units 10°m²/kg(m²/g) Material Mean Level Sr r (r) SR R (R) SRB-8B 133.1 0.71 2.00 1.5 1.39 3.92 2.9 SRB-8B2 126.7 0.56 1.58 1.2 2.02 5.73 4.5 SRB-8C 115.8 0.48 1.35 1.2 1.06 3.01 2.6 SRB-8A 77.2 0.41 1.17 1.5 1.15 3.26 4.2 SRB-8A2 76.0 0.47 1.32 1.7 1.23 3.49 4.6 SRB-8E 35.8 0.34 0.96 2.7 0.71 2.02 5.6 SRB-8F 35.4 0.33 0.93 2.6 0.69 1.95 5.5 SRB-8D 21.2 0.26 0.73 3.5 0.54 1.52 7.2 Average 77.6 Pooled Values 0.46 1.31 1.7 1.19 3.36 4.3 The preferred precision values are shown in bold text. in the normal and correct operation of the method. Two singletest results produced in different laboratories that differ bymore than the appropriate value from Table 4must besuspected of being from different populations and some appro-priate investigative or technical/commercial action taken. 12.5 Bias-In test method terminology， bias is the differencebetween 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 test property isexclusively defined by the test method. Bias， therefore， cannotbe determined. 13. Keywords 13.1 Brunauer/Emmett/Teller； carbon black， B.E.T.； nitro-gen adsorption； nitrogen surface area； statistical thicknesssurface area； surface area by multipoint B.E.T. method， exter-nal surface area ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. 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Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center， 222Rosewood Drive， Danvers， MA 01923， Tel： (978) 646-2600； http：//www.copyright.com/ Copyright O ASTM International， Barr Harbor Drive， PO Box C West Conshohocken， PA United States  前言当今社会，新能源行业快速发展，牵动电池行业也初步进入了革新的浪潮。锂电池是目前为止受关注程度最高的一类新型电池，其具备电压高、比能量、储存寿命长、高低温性能稳定的优点，但其相对较低的性价比和安全性也一直为人所诟病。在锂离子电池中，正极材料的性能直接影响到电池的性能，其成本的控制也决定电池成本高低。所以，寻找更高性能与性价比的电极材料早已成为了锂电池更新换代的重中之重。三元材料现在正作为取代钴酸锂正极的研究热点，安全性高的优点一直为大众所看好。在动力电池方面，需要考虑到续航时长，做到较高的功率和能量密度。想要达到这些要求，就必须要提高三元材料的比表面积，而三元材料的比表面一般与其前驱体的比表面成正比。所以，本文将就如何提高三元材料及前驱体的比表面测试精度展开讨论。本文实验所用仪器均为精微高博比表面仪。精微高博比表面仪分为静态法和动态法两种原理。静态比表面仪主要有高重复性及高精确度的孔径分析的特点；动态比表面仪在保证了高度重复的同时，更偏重了多站同时测试的高效。本文所应用的为JW-BK100C与JW-DX，所举测试方法对于精微高博的动态、静态仪器均适用。一、测试方法在测试三元材料比表面时，我们首先要取样，这就要考虑到样品的特性。电池中应用的三元材料是由LiCoO2、LiNiO2和LiMnO2三种材料混合而成，主要考虑到Ni、Co和Mn之间存在明显的协同效应，所以要以不同的配比来综合了这三种材料的优点。所以，不论是从产品质量的角度还是自身的研发出发，我们都应考虑样品在生产时的混合程度是否能够达到要求；准备实验时，是否多点取样。只有在规避了生产流程的误差风险后，我们才能以实测值为据来改善样品的生产工艺及配比，进而研发出目标产物。第二步，尽可能的精确称样量。在排除了样品可能有的车间生产的误差后，我们需要通过对工艺流程对比、条件控制差异和产物等进行初步分析，对样品的比表面积做出大概的预估。比表面积越大，称样量越小，反之，比表面积越小，称样量越大。BET方程为线性方程，只有称样量合适，实验所得的数据的线性越高，数据的线性越接近1，其数据就越符合BET方程，换言之，线性越接近1，所得的BET比表面积就越准确。通过一定的实验积累，可知的三元材料的比表面积普遍较小，所以建议在做静态实验时尽量称10g以上的样品，如能装满样品管下端就尽量振实、装满；动态实验尽量称7g以上，如能装满动态样品管就尽量多装，但需注意要振实样品，务必要留出空隙，供实验气体通过。第三步，确定预处理方案。由于空气中含有大量水分和混杂气体，样品又难免会接触到空气，水汽与样品表面生成的氢键在常温情况下极难断除，所以在实验开始前先对样品进行至少100℃的加热和抽真空的预处理非常必要。由于三元材料的耐热性普遍较差，所以加热温度一般不高于110℃。需要特殊注意的是，静态实验预处理顺序通常是先加热20min后再抽真空，但应用这个顺序来处理三元前驱体的话，前驱体样品易被氧化。因此，在测试三元前驱体的比表面时，预处理应该先抽真空，抽真空至0.1KPa后，充氮气至80KPa作保护气，然后抽真空到20Pa以下后，再加热，尽可能避免氧气残留。为了实验结果的精确性，在准备静态实验时，避免在预处理站进行三元前驱体的预处理，建议直接在分析站预处理与实验。由于称样量较大，为了保护仪器管路和确保复核失水后样品质量准确，实验设置中不要选择“液氮杯自动下降”，最终试验结束后，要先充气，再选择抽真空和下降液氮杯。样品管恢复室温后，务必要复核失水后参与实验的样品质量。一方面，核算出真正参与实验的样品的质量可以使实验值更加精准；另一方面，通过计算和对比处理样品前后的差值，我们可以进行样品工艺的影响因子分析，筛选出最佳的工艺组合，有助于相关研发部门进行工艺流程的改进。二、数据分析任选三个三元材料样品，预处理110℃真空脱气1h，按上述测试流程进行比表面积测试实验并测重复性，所得结果如下表所示：三元材料比表面对比数据仪器类型实验次数1号2号3号动态10.1810.3940.12120.1820.4100.11430.1920.4010.12040.1660.4010.12050.1650.3850.13060.1770.3820.11270.1800.3990.12580.1850.4020.108平均值0.178500.396750.11875标准差0.009150.009320.00715静态10.1620.3900.11120.1580.3790.10530.1580.3840.10440.1590.3850.11050.1550.3880.10160.1540.3920.10870.1540.3860.10380.1530.3870.112平均值0.156630.386370.10675标准差0.003110.003960.00406总平均值0.167560.391560.11275总标准差0.013080.008750.00836由于比表面积与其他物理量存在差异性，微观孔径等参数难以直接精确计算，相较而言没有绝对值，通常情况下都是以一定范围或是波动百分比计。因此我们无法就实测数值做直接对比和判定，但根据平均值及波动方差进行分析，可得出样品和仪器的双向情况。本文实验所用仪器均为精微高博制造，仪器性能稳定，经标准样品测试均已合格出厂。去除实验仪器本身的影响因素后，我们可就此样品的取样情况、比表面积范围及样品检测的不确定度展开探讨。图1 三元材料比表面的单值图 从样品方面考校，由图1单值图可以看出：同种检测原理下，同种样品的比表面数值较集中，可视作取样手法正确或所取样品已充分混合。 图2 三元材料比表面的区间图（均值的95%置信区间）由图2的区间图我们可以看出：当置信区间取为95%时，样品的比表面积数值均落于区间内，甚至静态法仪器较之动态法更为集中且趋近于平均值。从仪器特性的应用角度考虑，动态仪器适用于质量控制部门来料检测，四站同时实验，准确度与高效兼具；而静态仪器则更适合研发部门进行针对性研究，如混料特性及比表面对比、比例筛选等实验。高精确度的分析站不仅可以完成比表面分析，还可以测试孔径，通过选择不同的数据模型，应用范围更广，可获取数据更多。从实验的角度分析，建议三元前驱体材料选择静态仪器进行实验，出于满足材料对于真空度的要求，直接在分析站上预处理及实验。 精微高博对外承接样品比表面及孔径等测试项目，在实验方面积累了大量经验，尤其在控制实验不确定度上有较多心得，尤其重视实验方法的探究、尊重和保护样品特性，愿为我国材料行业发展尽绵薄之力。