1、Designation: C1274 10Standard Test Method forAdvanced Ceramic Specific Surface Area by PhysicalAdsorption1This standard is issued under the fixed designation C1274; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. 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 the determination of the surfacearea of advanced ceramic materials (in a solid form) based onmultil
3、ayer physisorption of gas in accordance with the methodof Brunauer, Emmett, and Teller (BET) (1)2and based onIUPAC Recommendations (1984 and 1994) (2) and (3). Thistest method specifies general procedures that are applicable tomany commercial physical adsorption instruments. This testmethod provides
4、 specific sample outgassing procedures forselected common ceramic materials, including: amorphous andcrystalline silicas, TiO2, kaolin, silicon nitride, silicon carbide,zirconium oxide, etc. The multipoint BET (1) equation alongwith the single point approximation of the BET equation arethe basis for
5、 all calculations. This test method is appropriate formeasuring surface areas of advanced ceramic powders down toat least 0.05 m2(if in addition to nitrogen, krypton at 77.35 Kis utilized as an adsorptive).1.2 This test method does not include all existing proce-dures appropriate for outgassing of a
6、dvanced ceramic materi-als. However, it provides a comprehensive summary of proce-dures recommended in the literature for selected types ofceramic materials. The investigator shall determine the appro-priateness of listed procedures.1.3 The values stated in SI units are to be regarded asstandard. St
7、ate all numerical values in terms of SI units unlessspecific instrumentation software reports surface area usingalternate units. In this case, provide both reported and equiva-lent SI units in the final written report. It is commonly acceptedand customary (in physical adsorption and related fields)
8、toreport the (specific) surface area of solids as m2/g, and, as aconvention, many instruments (as well as certificates of refer-ence materials) report surface area as m2g-1, instead of usingSI units (m2kg-1).1.4 This standard does not purport to address all of thesafety concerns, if any, associated
9、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:3D1993 Test Method for Precipitated Silica-Surface Area byMultipo
10、int BET Nitrogen AdsorptionE177 Practice for Use of the Terms Precision and Bias inASTM Test Methods2.2 ISO Standards:4ISO 9277 Determination of specific surface area of solids bygas adsorption using the BET methodISO 15901-2:2006 Pore size distribution and porosity ofsolid materials by mercury poro
11、simetry and gas adsorp-tion - Part 2Analysis of mesopores and macropores by gasadsorptionISO 8213:1986 Chemical products for industrial use -Sampling techniques-Solid chemical products in the formof particles varying from powders to coarse lumpsISO 18757 Fine ceramics (advanced ceramics, advancedtec
12、hnical ceramics) Determination of specific surfacearea of ceramic powders by gas adsorption using the BETmethod3. Terminology3.1 Definitions:53.1.1 adsorbate, nmaterial that has been retained by theprocess of adsorption.3.1.2 adsorbent, nany solid having the ability to concen-trate significant quant
13、ities of other substances on its surface.3.1.3 adsorption, nprocess in which molecules are con-centrated on a surface by chemical or physical forces, or both.3.1.4 adsorption isotherm, nrelation between the quantityof adsorbate and the equilibrium (relative) pressure of theadsorptive, at constant te
14、mperature.1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.03 onPhysical Properties and Non-Destructive Evaluation.Current edition approved Dec. 1, 2010. Published February 2011. Originallyapproved in 1994. Las
15、t previous edition approved in 2006 as C1274 00 (2006).DOI: 10.1520/C1274-10.2The boldface numbers in parenthesis refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For A
16、nnual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.5Compilation of ASTM Stand
17、ard Terminology, 8th ed, 1994.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4.1 DiscussionTypically, the amount adsorbed is pre-sented on an isotherm as volume i
18、n cm3STP (StandardTemperature and Pressure, that is, 273.15 K and 101325.02 Pa)normalized per mass of sample.3.1.5 adsorptive, nany substance available for adsorption.3.1.6 aliquot, na representative portion of a whole thatdivides the whole leaving a remainder.3.1.7 molecular cross-sectional area, n
19、molecular area ofthe adsorbate, that is, the area occupied by an adsorbatemolecule in the completed closed-packed monolayer.3.1.8 monolayer capacity, namount of the adsorbate (ex-pressed as number of moles, volume at STP, or weight) thatforms a closed-packed (complete) monomolecular layer overthe su
20、rface of the adsorbent.3.1.9 outgassing, nevolution of gas from a material undera vacuum or inert gas flow at or above ambient temperature.3.1.10 physical adsorption (van der Waals adsorption),nthe binding of an adsorbate to the surface of a solid byforces whose energy levels approximate those of co
21、ndensation.3.1.11 relative pressure, nratio of the equilibrium adsorp-tion pressure, p, to the saturation vapor pressure, p0.3.1.12 saturation vapor pressure, nvapor pressure of thebulk liquefied adsorbate at the temperature of adsorption.3.1.13 surface area, ntotal surface area of the surface ofa p
22、owder or solid including both external and accessibleinternal surfaces (from voids, cracks, open porosity, andfissures).3.1.13.1 DiscussionThe surface area may be calculatedby the BET equation (1) from gas adsorption data obtainedunder specific conditions. It is useful to express this value asthe sp
23、ecific surface area (see 3.1.13), that is, surface area perunit mass of sample (m2g-1).3.1.14 surface area (BET), ntotal surface area of a solidcalculated by the BET equation, (1) from gas adsorption ordesorption data obtained under specific conditions.3.1.15 surface area, specific (SSA), narea, per
24、 unit massof a granular or powdered or formed porous solid, of allexternal and internal surfaces that are accessible to a penetrat-ing gas or liquid.4. Summary of Test Method4.1 An appropriately sized (to provide at least the minimumsurface area required for reliable results; refer to requirementspr
25、ovided by the manufacturer of the instrument or apparatusbeing used) aliquot of sample is outgassed under appropriateconditions prior to analysis. For details on outgassing methodsand examples of specific outgassing conditions recommendedfor selected ceramic materials, see Section 11.4.2 The adsorpt
26、ive gas is admitted to a sample containerheld at a constant temperature. The amounts adsorbed aremeasured in equilibrium with the adsorptive gas pressure, p,and plotted against the relative pressure, p/p0, (where p0is thesaturation vapor pressure) to give an adsorption isotherm.Adsorption isotherms
27、may be obtained by volumetric (mano-metric) measurements or by the carrier gas flow measurements(flow volumetric method) and gravimetric techniques. This testmethod employs volumetric and flow volumetric methods.4.3 (Multipoint BET Analyses Only)The volume of gasadsorbed, or desorbed, is determined
28、for a minimum of fourrelative pressures within the linear BET transformation rangeof the physical adsorption, or desorption, isotherm character-istic of the advanced ceramic. The linear range is that whichresults in a least square correlation coefficient of 0.995 (pref-erably 0.999) or greater for t
29、he linear relationship (see linearform of BET equation, in Annex A1). Typically, the linearrange includes relative pressures between 0.05 and 0.30 (5)(6).However, microporous materials usually require use of a rangeof lower relative pressures (often a linear BET range can befound in the relative pre
30、ssure range from 0.01 to 0.1 (6)(7).For details, see Annex A2.4.4 (Single Point BET Analyses Only)The volume of gasadsorbed, or desorbed, is determined at the highest knownrelative pressure within the linear BET transformation range ofthe physical adsorption, or desorption, isotherm. Typically, arel
31、ative pressure of 0.30 is used. However, it may be necessaryto perform a multipoint analysis of the material first todetermine the optimum single point relative pressure.4.5 The physical adsorption instrument or apparatus mea-sures the total amount of gas adsorbed onto, or desorbed from,the sample u
32、nder analysis. The sample mass is then used tonormalize the measured results. Therefore, it is important touse an analytical balance to determine the sample weight. Themass of dry and outgassed sample, recorded to the nearest 0.1mg, shall be used. Any error in the sample weight will bepropagated int
33、o the final BET surface area result.4.6 Typical steps involved in the evaluation of the BETsurface area (see Annex A1 for calculation details):4.6.1 Transformation of a physisorption isotherm into theBET plot,4.6.2 An assessment of the monolayer capacity (multi-pointor single-point method). (See EqA
34、1.1-A1.6 inAnnexA1.), andNOTE 1Monolayer capacity can be expressed alternatively in terms ofSTP volume (Vm), weight (wm), or number of moles (nm), of adsorbate ina complete monolayer per1gofsample.4.6.3 Calculation of the specific surface area (SSA), as(seeEq A1.7 in Annex A1), which requires knowle
35、dge of themonolayer capacity as well as the effective molecular cross-sectional area of the adsorbate. Recommended customaryvalues for molecules of N2at 77.35 K, Ar at 87.27 K, and Krat 77.35 K, are provided in Table 1.5. Significance and Use5.1 Advanced ceramic powders and porous ceramic bodiesofte
36、n have a very fine particulate morphology and structure thatare marked by high surface-to-volume (S-V) ratios. Theseceramics with high S-V ratios commonly exhibit enhancedchemical reactivity and lower sintering temperatures. Resultsof many intermediate and final ceramic processing steps arecontrolle
37、d by, or related to, the specific surface area of theadvanced ceramic. The functionality of ceramic adsorbents,separation filters and membranes, catalysts, chromatographiccarriers, coatings, and pigments often depends on the amountand distribution of the porosity and its resulting effect on thespeci
38、fic surface area.5.2 This test method determines the specific surface area ofadvanced ceramic powders and porous bodies. Both suppliersand users of advanced ceramics can use knowledge of theC1274 102surface area of these ceramics for material development andcomparison, product characterization, desi
39、gn data, qualitycontrol, and engineering/ production specifications.6. Interferences6.1 This test method 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
40、 water or volatileorganic compounds, affect physical adsorption of the gas probemolecules used to measure surface area. Therefore, it isnecessary to remove these adsorbed contaminants prior tosurface area analysis. Generally, such procedure is performedby evacuating or purging the sample with inert
41、gas. Outgassingcan be accelerated by using elevated temperatures, provided noirreversible sample changes occur. Typical minimum vacuumlevels attained are 10-1Pa. Commonly used purging gases arehelium, nitrogen, or a mixture of the two. The outgassingprocedure is optimal or complete, or both when: (1
42、) duplicatesurface area analyses produce results within expected instru-ment repeatability limits, (2) constant residual vapor pressureis maintained upon isolation from the vacuum source, or (3)purging gas composition is unaffected while passing over thesample.6.2 The outgassing procedures and tempe
43、ratures shall notproduce any changes in composition, phase, or surface mor-phology of the powder specimens. The outgas temperaturelimits are determined by the stability limits of the powdersamples.7. Apparatus7.1 Manometric (Volumetric) ApparatusSee Test MethodD1993 and ISO 15901-2 for description o
44、f technology.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 automated versions of the classicalvacuum apparatus. Others may use a gravimetric technique todetermine
45、 the amount of adsorbed gas on the sample surface.Additionally, commercial instruments are available that mea-sure physical adsorption based on the dynamic flow method.7.3 Sample Cells, that when attached to the adsorptionapparatus will maintain isolation from the atmosphere equiva-lent to a specifi
46、ed (helium) leak rate determined by themanufacturer of the instrument.7.4 Heating Mantle or Equivalent, capable of maintaining atemperature in range from 100 to 300 6 10 C.7.5 Analytical Balance, with 0.1 mg sensitivity.7.6 Oven (Optional), gravity convection, capable of main-taining a temperature o
47、f 115 6 10 C.8. Reagents and Materials8.1 Liquid Nitrogen.8.2 Ultra-High Purity Nitrogen, 99.99 mol %, with the sumof O2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling lessthan 10 ppm, dry and oil-free, from a cylinder or other sourceof purified nitrogen.8.3 Ultra-High Purity Helium, 99.99 mol %, w
48、ith the sumof N2,O2,Ar,CO2, hydrocarbons (as CH4), and H2O totalingless than 10 ppm, dry and oil-free, from a cylinder or othersource of purified helium, if needed for determination of voidspace above sample.8.4 Ultra-High Purity Blended Nitrogen and Helium, dryand oil-free, from a cylinder or other
49、 source of blended gases.The actual composition of the blend shall be known. For usewith dynamic flow instruments only.8.5 Liquid Argon.8.6 Ultra-High Purity Argon, 99.99 mol %, with the sum ofO2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling lessthan 10 ppm, dry and oil-free, from a cylinder or other sourceof purified argon.8.7 Ultra-High Purity Krypton, 99.99 mol %, with the sumof O2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling lessthan 10 ppm, dry and oil-free, from a cylinder or other sourceof purified argon.8.8 Comments on Proper Selection of Adso
