1、Designation: B922 17Standard Test Method forMetal Powder Specific Surface Area by Physical Adsorption1This standard is issued under the fixed designation B922; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers determination of surface area ofmetal powders. The test method specifies general proceduresthat are appl
3、icable to many commercial physical adsorptioninstruments. The method provides specific sample outgassingprocedures for listed materials. It includes additional generaloutgassing instructions for other metals. The multipoint equa-tion of Brunauer, Emmett and Teller (BET),2along with thesingle point a
4、pproximation of the BET equation, forms thebasis for all calculations.1.2 This test method does not include all existing proce-dures appropriate for outgassing metallic materials. The pro-cedures included provided acceptable results for samplesanalyzed during interlaboratory testing. The investigato
5、r shalldetermine the appropriateness of listed procedures.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3.1 State all numerical values in terms of SI units unlessspecific instrumentation software reports surface area usi
6、ngalternate units. In this case, present both reported and equiva-lent SI units in the final written report. Many instruments reportsurface area as m2/g, instead of using correct SI units (m2/kg).1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use
7、. 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:3B215 Practices for Sampling Metal PowdersB243 Terminology of Powder Metallur
8、gy3. Terminology3.1 Definitions:3.1.1 Refer to Terminology B243 for additional terms spe-cific to metal powders.3.2 Definitions of Terms Specific to This Standard:3.2.1 adsorbate, nmaterial that has been retained by theprocess of adsorption.3.2.2 adsorbent, nany solid having the ability to concen-tr
9、ate or collect significant quantities of other substances on itssurface.3.2.3 adsorption, na process in which fluid molecules areconcentrated or collected on a surface by chemical or physicalforces, or both.3.2.4 adsorptive, nany substance available for adsorption.3.2.5 outgassing, nthe evolution of
10、 gas from a material ina vacuum or inert gas flow, at or above ambient temperature.3.2.6 physical adsorption (van der Waals adsorption),nthe binding of an adsorbate to the surface of a solid byforces whose energy levels approximate those of condensation.3.2.7 surface area, nthe total area of the sur
11、face 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, andTeller) equation from gas adsorption data obtained underspecific conditions. It is useful to express this val
12、ue as thespecific surface area, for example, surface area per unit mass ofsample (m2/kg).3.2.8 surface area (BET), nthe total surface area of a solidcalculated by the BET (Brunauer, Emmett, Teller) equation,from nitrogen adsorption or desorption data obtained underspecific conditions.3.2.9 surface a
13、rea, 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 appropriately sized sample (to provide at least theminimum surface area required for reliab
14、le results for theinstrument used) is outgassed under appropriate conditionsprior to analysis.1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-mittee B09.03 on Refractory Metal Powders.Current editi
15、on approved Jan. 1, 2017. Published February 2017. Originallyapproved in 2002. Last previous edition approved in 2010 as B92210. DOI:10.1520/B0922-17.2Brunauer, S., Emmett, P. H., and Teller, E. “Adsorption of Gases in Multimo-lecular Layers.” Journal of the American Chemical Society, Vol. 60, 1938,
16、 pp.309-319.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end
17、of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDeve
18、lopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14.2 Multipoint BET Analyses OnlyVolume of gasadsorbed, or desorbed, is determined as cm3corrected tostandard temperature and pressure (STP) for a minimum
19、 offour relative pressures within the linear BET transformationrange of the physical adsorption, or desorption, isothermcharacteristic of the metal. The linear range is that whichresults in a least squares correlation coefficient of 0.9999 orgreater for the relationship between BET transformation an
20、drelative pressure. Typically, the linear range includes relativepressures between 0.05 and 0.30.4.3 Single Point BET Analyses OnlyVolume of gasadsorbed, or desorbed, is determined as cm3corrected tostandard temperature and pressure (STP) at the highest knownrelative pressure within the linear BET t
21、ransformation range ofthe physical adsorption, or desorption, isotherm. Typically, arelative pressure of 0.30 is used. (It may be necessary to firstperform a multipoint analysis of the material to determine theoptimum single point relative pressure.)4.4 The sample is weighed to nearest 0.1 mg after
22、analysis.It is important to use an analytical balance to determine thesample mass. The physical adsorption instrument measures thetotal amount of gas adsorbed onto, or desorbed from, thesample under analysis. The sample mass is then used tonormalize the measured adsorption results. Any error in thes
23、ample mass will affect the 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 nm2ifnitrogen is used as the adsorptive. Use the appropriate valuerecommende
24、d 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 metals can benefit fromknowledge of the surface area of these materials. Results ofmany intermediate and final
25、 processing steps are controlled by,or related to, specific surface area of the metal. The perfor-mance of many sintered or cast metal structures may bepredicted from the specific surface area of the starting metalpowder, or all or a portion of the finished piece.6. Interferences6.1 This test method
26、 can be used to determine the internaland external surface of a powder or solid only after thesesurfaces 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 measu
27、re surface area. Therefore, it isnecessary to remove these adsorbed contaminants prior tosurface 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. Ty
28、pical minimum vacuumlevels attained are 10-1Pa. Typical flushing gases are helium,nitrogen, or 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 is
29、olation from the vacuum source,or when flushing gas composition is unaffected while passingover the sample.7. Apparatus7.1 Commercial instruments are available from severalmanufacturers for the measurement of specific surface area byphysical adsorption. Some are automated versions of theclassical va
30、cuum apparatus. Others make use of balancedadsorption technology. Additionally, commercial instrumentsare available which measure physical adsorption based on thedynamic flow method.7.2 Analytical Balance, capable of weighing to the nearest0.1 mg.8. Reagents and Materials8.1 Liquid Nitrogen.8.2 Nitr
31、ogen, 99.999 mole percent, with the sum of O2,argon, CO2, hydrocarbons (as CH4), and H2O totaling less than10 parts per million; dry and oil-free; cylinder, or other sourceof purified nitrogen.8.3 Helium, 99.999 mole percent, with the sum of N2,O2,argon, CO2, hydrocarbons (as CH4), and H2O totaling
32、less than10 parts per million; dry and oil-free; cylinder, or other sourceof purified helium, if needed for determination of void spaceabove sample.8.4 Blended Nitrogen and Helium, dry and oil-free;cylinder, or other source of blended gases. The actual compo-sition of the blend must be known. For us
33、e with dynamic flowinstruments only.9. Hazards9.1 Precautions applying to the use of liquid nitrogen andcompressed gases should be observed.10. Sampling, Test Specimens, and Test Units10.1 It is important that the test portion being analyzedrepresent the larger bulk sample from which it is taken. Th
34、ebulk sample should be homogenized before any sampling takesplace. Best results are obtained when a flowing bulk material istemporarily diverted into a collector for an appropriate time. Itis better to sample the entire flow for a short time than tosample a portion of the flow for a longer time. Col
35、lectingseveral small aliquants and combining them improves thereliability of the sampling process. Rotating rifflers are avail-able commercially which satisfy these sampling requirements.Refer to Practices B215 for information on the use of a chutesample splitter.11. Calibration and Standardization1
36、1.1 Follow manufacturers instructions for calibration andoperational verification of the instrument.12. Outgassing12.1 Weigh (to nearest 0.1 mg) a clean, empty sample tube,along with stopper or seal. Record the empty tube mass.B922 17212.2 Add test portion to empty sample tube. Sample quan-tity shou
37、ld be sufficient to satisfy minimum surface area asrequired by manufacturer.12.3 Attach prepared sample tube to outgassing port ofinstrument. Secure heating mantle or oven around sample tubeat the time appropriate for sample.12.4 Initiate outgassing program according to manufactur-ers instructions.
38、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, or for prescribedoutgassing time, or both. Samples analyzed during the inter-laboratory study w
39、ere heated for2hat200C.12.5 Remove heating mantle or oven from sample tube.Allow sample tube to cool to ambient temperature. Removeand seal sample tube according to manufacturers instructions.12.6 Weigh sample tube (to nearest 0.1 mg) to obtainsample and tube mass. Record mass. Subtract empty sample
40、tube mass determined in 12.1 to obtain outgassed sample mass.Record calculated mass.13. Procedure13.1 Attach appropriately prepared sample holder to analy-sis port according to manufacturers instructions. Include anyrequired hardware.13.1.1 Use nitrogen as adsorptive for all tests. Use blendednitrog
41、en and helium with dynamic flow instruments. Use purenitrogen with volumetric instruments.13.1.2 Use helium to determine sample holder void spacewith volumetric instruments as necessary.13.1.3 Use liquid nitrogen as cryogen for all tests.13.2 Automated Instruments OnlySelect, or input, desiredanalys
42、is and report parameters.13.2.1 Multipoint BET Analyses OnlyUse at least fouranalysis points in the linear BET transformation range of theisotherm characteristic of the sample. If necessary, input theoutgassed sample mass. (The final mass should be determinedand entered after the analysis.)13.2.2 Si
43、ngle Point BET Analyses OnlyUse highest rela-tive pressure known to be in the linear BET transformationrange of the isotherm. If necessary, input the outgassed samplemass. (The final mass should be determined and entered afterthe analysis.)13.3 Dynamic Flow Instruments OnlyCollect data pointsas volu
44、me of gas desorbed versus relative pressure.13.3.1 Multipoint BET Analyses OnlyUse at least fouranalysis points in the linear BET transformation range of theisotherm characteristic of the sample.13.3.2 Single Point BET Analyses OnlyUse highest rela-tive pressure known to be in the linear BET transfo
45、rmationrange of the isotherm.13.4 Perform analysis using the specified conditions accord-ing to instrument manufacturers instructions.13.5 When the analysis has finished and the sample haswarmed to room temperature, remove and seal the sample tube.Dry tube and weigh (to nearest 0.1 mg). Record the f
46、inal tubeand sample mass. Subtract the empty tube mass recorded in12.1 to obtain the final sample mass. Record final sample mass.13.6 Automated Instruments OnlyEdit the file containingsample information to include the final sample mass. Generatefinal sample report.14. Calculations14.1 Automated Inst
47、ruments OnlySoftware automaticallycalculates results for the chosen reports using the final massinput in 13.6.14.2 Dynamic Flow Instruments OnlyFollow manufactur-ers instructions for multipoint, or single point, calculations.Use the final sample mass determined in 13.5 when calculatingthe specific s
48、urface area.15. Report15.1 Report the following information:15.1.1 Complete sample identification.15.1.2 Collected isotherm point(s) as volume adsorbed, ordesorbed, versus relative pressure. Note whether adsorption ordesorption isotherm is used. Note any units used other thanstandard.15.1.3 Analysis
49、 gas used (with cross sectional area if otherthan nitrogen).15.1.4 BET specific surface area. Note any units used otherthan standard.15.1.5 Final sample mass. Note any units used other thanstandard.15.1.6 Sample outgassing method, including total time andoutgassing temperature(s).16. Precision and Bias16.1 The precision of Test Method B922 has not been fullydetermined. The repeatability standard deviation of singlepoint specific surface area for one tungsten carbide sample hasbeen determined to be 60.6 % relative standard deviation,based upon analyses in on
