1、Designation: C 1274 00 (Reapproved 2006)Standard Test Method forAdvanced Ceramic Specific Surface Area by PhysicalAdsorption1This standard is issued under the fixed designation C 1274; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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. Scope1.1 This test method covers determination of surface area ofadvanced ceramic materials. This test method sp
3、ecifies generalprocedures that are applicable to many commercial physicaladsorption instruments. This test method provides specificsample outgassing procedures for listed materials, includingsilicon carbide, silicon nitride, and zirconium oxide. It includesadditional general outgassing instructions
4、for other advancedceramic materials. The multipoint equation of Brunauer, Em-mett and Teller2(BET) along with the single point approxima-tion of the BET equation form the basis for all calculations.1.2 This test method does not include all existing proce-dures appropriate for outgassing advanced cer
5、amic materials.The included procedures provided acceptable results forsamples analyzed during round robin testing. The investigatormust determine the appropriateness of listed procedures.1.3 This test method uses SI units as standard. State allnumerical values in terms of SI units unless specific in
6、stru-mentation software reports surface area using alternate units. Inthis case, present both reported and equivalent SI units in thefinal written report. Many instruments report surface area asm2/g, instead of using correct SI units (m2/kg).1.4 This standard does not purport to address all of thesa
7、fety 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.2. Referenced Documents2.1 ASTM Standards:3D 1993 Test Method for Precipi
8、tated Silica-SurfaceArea byMultipoint BET Nitrogen AdsorptionE 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3. Terminology3.1 Definitions:43.1.1 adsorbate, nmaterial that has been retained by theprocess of adsorption.3.1.2 adsorbent, nany solid having the ability to concen
9、-trate significant quantities of other substances on its surface.3.1.3 adsorption, na process in which fluid molecules areconcentrated on a surface by chemical or physical forces, orboth.3.1.4 adsorptive, nany substance available for adsorption.3.1.5 aliquant, na representative portion of a whole th
10、atdivides the whole leaving a remainder.3.1.6 outgassing, nthe evolution of gas from a material ina vacuum or inert gas flow, at or above ambient temperature.3.1.7 physical adsorption (van der Waals adsorption),nthe binding of an adsorbate to the surface of a solid byforces whose energy levels appro
11、ximate those of condensation.3.1.8 surface area, nthe total area of the surface of apowder or solid including both external and accessible internalsurfaces (from voids, cracks, open porosity, and fissures). Thearea may be calculated by the BET (Brunauer, Emmett, andTeller2) equation from gas adsorpt
12、ion data obtained underspecific conditions. It is useful to express this value as thespecific surface area, for example, surface area per unit weightof sample (m2/g).3.1.9 surface area (BET), n the total surface area of asolid calculated by the BET (Brunauer, Emmett, Teller2)equation, from nitrogen
13、adsorption or desorption data obtainedunder specific conditions.3.1.10 surface area, specific, nthe area, per unit mass of agranular or powdered or formed porous solid, of all externalplus internal surfaces that are accessible to a penetrating gas orliquid.4. Summary of Test Method4.1 An appropriate
14、 sized sample (to provide at least theminimum surface area required for reliable results for the1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.03 onPhysical Properties and Performance.Current edition approved
15、 Jan. 1, 2006. Published January 2006. Originallyapproved in 1994. Last previous edition approved in 2000 as C 1274 00.2Brunauer, S., Emmett, P. H., and Teller, E., J. Am. Chem. Soc. 60, 1938, pp.309319.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Ser
16、vice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Compilation of ASTM Standard Terminology, 8th ed, 1994.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, U
17、nited States.instrument or apparatus used) is outgassed under appropriateconditions prior to analysis.4.2 (Multipoint BET Analyses Only)Volume of gas ad-sorbed, or desorbed, is determined for a minimum of fourrelative pressures within the linear BET transformation rangeof the physical adsorption, or
18、 desorption, isotherm character-istic of the advanced ceramic. The linear range is that whichresults in a least square correlation coefficient of 0.999 (pref-erably 0.9999) or greater for the linear relationship used in theBET graph (1(adsorbed volume * (1/relative pressure 1). Typically, thelinear
19、range includes relative pressures between 0.05 and 0.30,however, microporous materials usually require use of a rangeof lower relative pressures, such as 0.01 to 0.10.4.3 (Single Point BET Analyses Only)Volume of gasadsorbed, or desorbed, is determined at the highest knownrelative pressure within th
20、e linear BET transformation range ofthe physical adsorption, or desorption, isotherm. Typically, arelative pressure of 0.30 is used. (It may be necessary toperform a multipoint analysis of the material first to determinethe optimum single point relative pressure.)4.4 The sample is accurately weighed
21、 (to at least 1% of thesample mass) after analysis. It is important to use an analyticalbalance to determine the sample weight. The physical adsorp-tion instrument or apparatus measures the total amount of gasadsorbed onto, of desorbed from, the sample under analysis.The sample weight is then used t
22、o normalize the measuredresults. Any error in the sample weight will be propagated intothe final BET surface area.4.5 Calculations are based on the BET equation, as requiredby the instrument being used for the determination. The crosssectional area for the adsorbate is taken to be 0.162 nm2ifnitroge
23、n is used as the adsorptive. Use the appropriate valuerecommended by the instrument manufacturer for adsorptivesother than nitrogen. Report this cross sectional area with theBET surface area results.5. Significance and Use5.1 Both suppliers and users of advanced ceramics canbenefit from knowledge of
24、 the surface area of these materials.Results of many intermediate and final processing steps arecontrolled by, or related to, specific surface area of theadvanced ceramic.6. Interferences6.1 This test method can be used to determine the internaland external surface of a powder or solid only after th
25、esesurfaces have been cleaned of any physically adsorbed mol-ecules. Such adsorbed species, for example, water or volatileorganic compounds, prevent physical adsorption of the gasprobe molecules used to measure surface area. Therefore, it isnecessary to remove these adsorbed contaminants prior tosur
26、face area analysis. Generally, such outgassing is performedby evacuating or flushing the sample. Outgassing can beaccelerated by using elevated temperatures, provided no irre-versible sample changes occur. Typical minimum vacuumlevels attained are 101Pa. Typical flushing gases are helium,nitrogen, o
27、r a mixture of the two. Outgassing is complete whenduplicate surface area analyses produce results within expectedinstrument repeatability limits, when a constant residual vaporpressure is maintained upon isolation from the vacuum source,or when flushing gas composition is unaffected while passingov
28、er the sample.7. Apparatus7.1 Classical Vacuum ApparatusRefer to Test MethodD 1993 for apparatus description.7.2 Automated and Dynamic Flow InstrumentsCommercial instruments are available from several manufac-turers for the measurement of specific surface area by physicaladsorption. Some are automat
29、ed versions of the classicalvacuum apparatus. Others may use a gravimetric technique todetermine the amount of adsorbed gas on the sample surface.Additionally, commercial instruments are available whichmeasure physical adsorption based on the dynamic flowmethod.8. Reagents and Materials8.1 Liquid Ni
30、trogen.8.2 Nitrogen, 99.99 mole percent, with the sum of O2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling less than 10ppm, dry and oil-free, cylinder, or other source of purifiednitrogen.8.3 Helium, 99.99 mole percent, with the sum of N2,O2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling less than
31、 10ppm, dry and oil-free, cylinder, or other source of purifiedhelium, if needed for determination of void space abovesample.8.4 Blended Nitrogen and Helium, dry and oil-free, cylinder,or other source of blended gases. The actual composition of theblend must be known. For use with dynamic flow instr
32、umentsonly.9. Sampling, Test Specimens, and Test Units9.1 No specific instructions are given. However, it is impor-tant that the aliquant being analyzed represent the larger bulksample from which it is taken. The bulk sample should behomogenized before any sampling takes place. Best results areobtai
33、ned when a flowing bulk material is temporarily divertedinto a collector for an appropriate time. It is better to samplethe entire flow for a short time than to sample a portion of theflow for a longer time. Collecting several small aliquants andcombining them improves the reliability of the samplin
34、gprocess. Rotating rifflers are available that satisfy these re-quirements.10. Calibration and Standardization10.1 Classical Vacuum ApparatusRefer to Test MethodD 1993 for calibration procedures.10.2 Automated and Dynamic Flow InstrumentsFollowmanufacturers instructions for calibration and operation
35、alverification of the instrument.11. Outgassing11.1 Classical Vacuum ApparatusRefer to Test MethodD 1993 for outgassing procedures.11.2 Automated and Dynamic Flow Instruments:11.2.1 Weigh (to the nearest 0.1 mg) clean, empty sampletube, along with stopper or seal. Record the empty tube weight.C 1274
36、 00 (2006)211.2.2 Add representative sample to empty sample tube.Sample quantity should be sufficient to satisfy minimumsurface area as required by manufacturer.11.2.3 Attach prepared sample tube to outgassing port ofinstrument. Secure heating mantle or oven around sample tubeat the time appropriate
37、 for sample.11.2.4 Initiate outgassing program according to manufactur-ers instructions. Program mantle or oven for initial outgassingtemperature. Increase temperature as appropriate for thesample. Allow sample to continue to outgas until prescribedvacuum level or detector signal is achieved and/or
38、for pre-scribed outgassing time. Be aware that heating of the samplewithout a sufficient vacuum can lead to hydrothermal condi-tions, which then could result in changes in the sample. Thus,it is recommended to assure a vacuum of 1 Pa or better at alltimes during the heat-out. Outgassing without thos
39、e vacuumconditions can be used once an initial test on similar sampleshas confirmed that no changes in the sample surface area occur.This is especially important when the flow gas (He) techniqueis used for the out-gassing process.NOTE 1Specific outgassing information will be added after roundrobin t
40、est samples are selected.11.2.5 Remove heating mantle or oven from sample tube.Allow sample tube to cool to ambient temperature. Removeand seal sample tube according to manufacturers instructions.11.2.6 Weigh sample tube (to the nearest 0.1 mg) to obtainsample and tube weight. Record weight. Subtrac
41、t emptysample tube weight determined in 11.2 to obtain outgassedsample weight. Record calculated weight.12. Procedure12.1 Classical Vacuum ApparatusRefer to Test MethodD 1993 for analysis procedures.12.2 Automated and Dynamic Flow InstrumentsAttachappropriately prepared sample holder to analysis por
42、t accord-ing to manufacturers instructions. Include any required hard-ware.12.3 (Automated Instruments Only)Select, or input, de-sired analysis and report parameters.12.3.1 (Multipoint BET Analyses Only)Use at least fouranalysis points in the linear BET transformation range of theisotherm characteri
43、stic of the sample. If necessary, input theoutgassed sample weight. (The final weight should be deter-mined and entered after the analysis.)12.3.2 (Single Point BET Analyses Only)Use highestrelative pressure known to be in the linear BET transformationrange of the isotherm. If necessary, input the o
44、utgassed sampleweight. (The final weight should be determined and enteredafter the analysis.)12.4 (Dynamic Flow Instruments Only)Collect datapoints as volume of gas desorbed versus relative pressure:12.4.1 (Multipoint BET Analyses Only)Use at least fouranalysis points in the linear BET transformatio
45、n range of theisotherm characteristic of the sample.12.4.2 (Single Point BET Analyses Only)Use highestrelative pressure known to be in the linear BET transformationrange of the isotherm.12.5 Perform analysis using the specified conditions accord-ing to instrument manufacturers instructions.12.6 When
46、 the analysis has finished and the sample haswarmed to room temperature, remove and seal the sample tube.Dry tube and weigh (to the nearest 0.1 mg). Record the finaltube and sample weight. Subtract the empty tube weightrecorded in 11.2 to obtain the final sample weight. Record finalsample weight.12.
47、7 (Automated Instruments Only)Edit the file contain-ing sample information to include the final sample weight.Generate final sample report.13. Calculation13.1 Classical Vacuum ApparatusRefer to Test MethodD 1993 for calculations.13.2 Automated and Dynamic Flow Instruments:TABLE 1 Precision for Singl
48、e Point and Multipoint BET MethodsPrecisionSingle Point BET MethodMaterialNumber ofLaboratoriesSurface Area(average)RepeatabilityStandardDeviation SrReproducibilityStandardDeviation SRRepeatabilityLimitReproducibilityLimitRepeatabilityC.V.ReproducibilityC.V.A1N 6 2.82 0.09 0.12 0.24 0.24 3.1 % 4.3 %
49、Si3N4 (SNT) 17 9.30 0.24 0.38 0.66 1.05 2.6 % 4.1 %Si3N4 (SNR) 6 12.55 0.79 0.86 2.18 2.38 6.3 % 6.8 %SiC 16 13.27 0.25 0.67 0.69 1.86 1.9 % 5.1 %Y2O3-ZrO2 9 17.72 0.34 0.89 0.95 2.47 1.9 % 5.0 %This table was calculated using the relationship: limit = 1.96 3=2 3 standard deviationPrecisionMulti Point BET MethodMaterialNumber ofLaboratoriesSurface Area(average)RepeatabilityStandardDeviation SrReproducibilityStandardDeviation SRRepeatabilityLimitReproducibilityLimitRepeatabilityC.V.ReproducibilityC.V.A1N 6 2.83 0.15 0.22 0.42 0.62 5.3 % 7.9 %Si3
