1、Designation: C1274 10 C1274 12Standard 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
2、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. Scope*1.1 This test method covers the determination of the surface area of advanced ceramic materials (in a solid form) base
3、d onmultilayer physisorption of gas in accordance with the method of Brunauer, Emmett, and Teller (BET) (1)2 and based on IUPACRecommendations (1984 and 1994) (2) and (3). This test method specifies general procedures that are applicable to manycommercial physical adsorption instruments. This test m
4、ethod provides specific sample outgassing procedures for selectedcommon ceramic materials, including: amorphous and crystalline silicas, TiO2, kaolin, silicon nitride, silicon carbide, zirconiumoxide, etc. The multipoint BET (1) equation along with the single point approximation of the BET equation
5、are the basis for allcalculations. This test method is appropriate for measuring surface areas of advanced ceramic powders down to at least 0.05 m2(if in addition to nitrogen, krypton at 77.35 K is utilized as an adsorptive).1.2 This test method does not include all existing procedures appropriate f
6、or outgassing of advanced ceramic materials.However, it provides a comprehensive summary of procedures recommended in the literature for selected types of ceramicmaterials. The investigator shall determine the appropriateness of listed procedures.1.3 The values stated in SI units are to be regarded
7、as standard. State all numerical values in terms of SI units unless specificinstrumentation software reports surface area using alternate units. In this case, provide both reported and equivalent SI units inthe final written report. It is commonly accepted and customary (in physical adsorption and r
8、elated fields) to report the (specific)surface area of solids as m2/g, and, as a convention, many instruments (as well as certificates of reference materials) report surfacearea as m2 g-1, instead of using SI units (m2 kg-1).1.4 This standard does not purport to address all of the safety concerns, i
9、f 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.2. Referenced Documents2.1 ASTM Standards:3D1993 Test Method for Precipitated Silica-Surface
10、 Area by Multipoint BET Nitrogen AdsorptionE177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods2.2 ISO Standards:4ISO 9277 Determination of specific surface area of solids by gas adsorption using the BET methodISO 15901-2:2006 Pore size distribution and porosity of solid materi
11、als by mercury porosimetry and gas adsorption - Part 2Analysis of mesopores and macropores by gas adsorptionISO 8213:1986 Chemical products for industrial use - Sampling techniques-Solid chemical products in the form of particlesvarying from powders to coarse lumpsISO 18757 Fine ceramics (advanced c
12、eramics, advanced technical ceramics) Determination of specific surface area of ceramicpowders by gas adsorption using the BET method1 This test method is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.03 on Physical Propertiesa
13、nd Non-Destructive Evaluation.Current edition approved Dec. 1, 2010Aug. 1, 2012. Published February 2011November 2012. Originally approved in 1994. Last previous edition approved in 20062010as C1274 00C1274 10. (2006). DOI: 10.1520/C1274-10.10.1520/C1274-12.2 The boldface numbers in parenthesis refe
14、r to the list of references at the end of this standard.3 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4
15、Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been
16、 made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.
17、*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions: 53.1.1 adsorbate, nmaterial that has been retained by the process of adsorption.3.1.2 adso
18、rbent, nany solid having the ability to concentrate significant quantities of other substances on its surface.3.1.3 adsorption, nprocess in which molecules are concentrated on a surface by chemical or physical forces, or both.3.1.4 adsorption isotherm, nrelation between the quantity of adsorbate and
19、 the equilibrium (relative) pressure of theadsorptive, at constant temperature.3.1.4.1 DiscussionTypically, the amount adsorbed is presented on an isotherm as volume in cm3 STP (Standard Temperature and Pressure, that is,273.15 K and 101325.02 Pa) normalized per mass of sample.3.1.5 adsorptive, nany
20、 substance available for adsorption.3.1.6 aliquot, na representative portion of a whole that divides the whole leaving a remainder.3.1.7 molecular cross-sectional area, nmolecular area of the adsorbate, that is, the area occupied by an adsorbate moleculein the completed closed-packed monolayer.3.1.8
21、 monolayer capacity, namount of the adsorbate (expressed as number of moles, volume at STP, or weight) that forms aclosed-packed (complete) monomolecular layer over the surface of the adsorbent.3.1.9 outgassing, nevolution of gas from a material under a vacuum or inert gas flow at or above ambient t
22、emperature.3.1.10 physical adsorption (van der Waals adsorption), nthe binding of an adsorbate to the surface of a solid by forces whoseenergy levels approximate those of condensation.3.1.11 relative pressure, nratio of the equilibrium adsorption pressure, p, to the saturation vapor pressure, p0.3.1
23、.12 saturation vapor pressure, nvapor pressure of the bulk liquefied adsorbate at the temperature of adsorption.3.1.13 surface area, ntotal surface area of the surface of a powder or solid including both external and accessible internalsurfaces (from voids, cracks, open porosity, and fissures).3.1.1
24、3.1 DiscussionThe surface area may be calculated by the BET equation (1) from gas adsorption data obtained under specific conditions. It isuseful to express this value as the specific surface area (see 3.1.13), that is, surface area per unit mass of sample (m2 g-1).3.1.14 surface area (BET), ntotal
25、surface area of a solid calculated by the BET equation, (1) from gas adsorption or desorptiondata obtained under specific conditions.3.1.15 surface area, specific (SSA), narea, per unit mass of a granular or powdered or formed porous solid, of all external andinternal surfaces that are accessible to
26、 a penetrating gas or liquid.4. Summary of Test Method4.1 An appropriately sized (to provide at least the minimum surface area required for reliable results; refer to requirementsprovided by the manufacturer of the instrument or apparatus being used) aliquot of sample is outgassed under appropriatec
27、onditions prior to analysis. For details on outgassing methods and examples of specific outgassing conditions recommended forselected ceramic materials, see Section 11.4.2 The adsorptive gas is admitted to a sample container held at a constant temperature. The amounts adsorbed are measuredin equilib
28、rium with the adsorptive gas pressure, p, and plotted against the relative pressure, p/p0, (where p0 is the saturation vaporpressure) to give an adsorption isotherm. Adsorption isotherms may be obtained by volumetric (manometric) measurements or bythe carrier gas flow measurements (flow volumetric m
29、ethod) and gravimetric techniques. This test method employs volumetric andflow volumetric methods.4.3 (Multipoint BET Analyses Only)The volume of gas adsorbed, or desorbed, is determined for a minimum of four relativepressures within the linear BET transformation range of the physical adsorption, or
30、 desorption, isotherm characteristic of theadvanced ceramic. The linear range is that which results in a least square correlation coefficient of 0.995 (preferably 0.999) orgreater for the linear relationship (see linear form of BET equation, in Annex A1). Typically, the linear range includes relativ
31、epressures between 0.05 and 0.30 (5)(6). However, microporous materials usually require use of a range of lower relative pressures(often a linear BET range can be found in the relative pressure range from 0.01 to 0.1 (6)(7). For details, see Annex A2.5 Compilation of ASTM Standard Terminology, 8th e
32、d, 1994.C1274 1224.4 (Single Point BET Analyses Only)The volume of gas adsorbed, or desorbed, is determined at the highest known relativepressure within the linear BET transformation range of the physical adsorption, or desorption, isotherm. Typically, a relativepressure of 0.30 is used. However, it
33、 may be necessary to perform a multipoint analysis of the material first to determine theoptimum single point relative pressure.4.5 The physical adsorption instrument or apparatus measures the total amount of gas adsorbed onto, or desorbed from, thesample under analysis. The sample mass is then used
34、 to normalize the measured results. Therefore, it is important to use ananalytical balance to determine the sample weight. The mass of dry and outgassed sample, recorded to the nearest 0.1 mg, shallbe used. Any error in the sample weight will be propagated into the final BET surface area result.4.6
35、Typical steps involved in the evaluation of the BET surface area (see Annex A1 for calculation details):4.6.1 Transformation of a physisorption isotherm into the BET plot,4.6.2 An assessment of the monolayer capacity (multi-point or single-point method). (See Eq A1.1-A1.6 in Annex A1.), andNOTE 1Mon
36、olayer capacity can be expressed alternatively in terms of STP volume (Vm), weight (wm), or number of moles ( nm), of adsorbate in acomplete monolayer per 1 g of sample.4.6.3 Calculation of the specific surface area (SSA), as (see Eq A1.7 in Annex A1), which requires knowledge of the monolayercapaci
37、ty as well as the effective molecular cross-sectional area of the adsorbate. Recommended customary values for moleculesof N2 at 77.35 K, Ar at 87.27 K, and Kr at 77.35 K, are provided in Table 1.5. Significance and Use5.1 Advanced ceramic powders and porous ceramic bodies often have a very fine part
38、iculate morphology and structure that aremarked by high surface-to-volume (S-V) ratios. These ceramics with high S-V ratios commonly exhibit enhanced chemicalreactivity and lower sintering temperatures. Results of many intermediate and final ceramic processing steps are controlled by, orrelated to,
39、the specific surface area of the advanced ceramic. The functionality of ceramic adsorbents, separation filters andmembranes, catalysts, chromatographic carriers, coatings, and pigments often depends on the amount and distribution of theporosity and its resulting effect on the specific surface area.5
40、.2 This test method determines the specific surface area of advanced ceramic powders and porous bodies. Both suppliers andusers of advanced ceramics can use knowledge of the surface area of these ceramics for material development and comparison,product characterization, design data, quality control,
41、 and engineering/ production specifications.TABLE 1 Cross-Sectional Areas of Selected Commonly UsedAdsorptivesAdsorptive Temperature, K Recommended Valueof Cross-Sectional Area, nm2Nitrogen 77.35 0.162AArgon 77.35 0.138BArgon 87.27 0.142Krypton 77.35 0.202CAVery often the orientation of the adsorbed
42、 N2 molecules (having quadruplemoment) can be affected by specific interactions with polar groups on the surfaceof adsorbent (i.e. in case of highly polar surfaces, such as with hydroxylated oxidesurface groups). (8-10) This can lead to a significant reduction in the effectivecross-sectional area. I
43、f the standard value for N2 molecule (0.162 nm2 at 77.35 K)is used, the BET surface area of hydroxylated silica surfaces can be overestimatedby 20%. Therefore, in case of ceramics with surfaces of high polarity, argon (whichis a chemically inert monoatomic gas) adsorption at 87.3 K is an alternative
44、adsorptive recommended for surface area determination, since the cross-sectionalarea of argon (0.142 nm2 at 87.27 K) is less sensitive to differences in structure ofthe adsorbent surface.BThe use of argon at 77.35 K (which is approximately 6.5 K below the triple pointof bulk argon) is considered to
45、be less reliable than nitrogen, because at 77.35 Kthe structure of the argon monolayer may be highly dependent on the surfacechemistry of the adsorbent. The cross-sectional area for argon at 77.35 K is notwell defined. The value of 0.138 nm2, as given in the table is based on theassumption of a clos
46、ed-packed liquid monolayer, and can also be considered to bethe customary value.CThe use of krypton at 77.35 K allows to manometrically measure very low uptakeswith acceptable accuracy. However, similar to argon at 77.35 K, krypton at 77.35K is significantly below the triple point temperature of bul
47、k krypton (approximately38.5 K), and the structure of the krypton monolayer may be strongly affected by thesurface chemistry of the adsorbent. This will directly influence the effective kryptoncross-sectional area. The value given in the table can be considered to be acustomary value.C1274 1236. Int
48、erferences6.1 This test method can be used to determine the internal and external surface of a powder or solid only after these surfaceshave been cleaned of any physically adsorbed molecules. Such adsorbed species, for example water or volatile organic compounds,affect physical adsorption of the gas
49、 probe molecules used to measure surface area. Therefore, it is necessary to remove theseadsorbed contaminants prior to surface area analysis. Generally, such procedure is performed by evacuating or purging the samplewith inert gas. Outgassing can be accelerated by using elevated temperatures, provided no irreversible sample changes occur.Typical minimum vacuum levels attained are 10-1 Pa. Commonly used purging gases are helium, nitrogen, or a mixture of the two.The outgassing procedure is optimal or complete, or both when: (1) duplicate surface area ana
