1、raising standards worldwide NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BSI Standards Publication BS ISO 9277:2010 Determination of the specific surface area of solids by gas adsorption BET methodBS ISO 9277:2010 BRITISH STANDARD National foreword This British Standard is
2、the UK implementation of ISO 9277:2010. The UK participation in its preparation was entrusted to Technical Committee LBI/37, Particle characterization including sieving. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purpo
3、rt to include all the necessary provisions of a contract. Users are responsible for its correct application. BSI 2010 ISBN 978 0 580 62592 3 ICS 17.040.20; 19.120 Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was published under the authority
4、 of the Standards Policy and Strategy Committee on 30 September 2010. Amendments issued since publication Date Text affectedBS ISO 9277:2010Reference number ISO 9277:2010(E) ISO 2010INTERNATIONAL STANDARD ISO 9277 Second edition 2010-09-01 Determination of the specific surface area of solids by gas
5、adsorption BET method Dtermination de laire massique (surface spcifique) des solides par adsorption de gaz Mthode BET BS ISO 9277:2010 ISO 9277:2010(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shal
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10、 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2010 All rights reservedBS ISO 9277:2010 ISO 9277:2010(E) ISO 2010 All rights reserved iiiContents Page Foreword iv 1 Scope1 2 Normative references1 3 Terms and definitions .1 4 Symbols and abbreviated terms 3 5 Principle4 6
11、 Procedure.6 6.1 Sample preparation .6 6.2 Experimental conditions.9 6.3 Measuring methods for the assessment of the amount of adsorbed gas.9 7 Evaluation of adsorption data12 7.1 General .12 7.2 Multipoint determination.12 7.3 Single-point determination.14 8 Test report14 9 Use of reference materia
12、ls15 Annex A (informative) Cross-sectional areas of some frequently used adsorptives 16 Annex B (informative) Certified reference materials for the BET method 17 Annex C (informative) Surface area of microporous materials19 Bibliography23 BS ISO 9277:2010 ISO 9277:2010(E) iv ISO 2010 All rights rese
13、rvedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which
14、 a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all mat
15、ters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circu
16、lated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsi
17、ble for identifying any or all such patent rights. ISO 9277 was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving, Subcommittee SC 4, Particle characterization. This second edition cancels and replaces the first edition (ISO 9277:1995), which has been technically
18、 revised. BS ISO 9277:2010 INTERNATIONAL STANDARD ISO 9277:2010(E) ISO 2010 All rights reserved 1Determination of the specific surface area of solids by gas adsorption BET method 1 Scope This International Standard specifies the determination of the overall (see Note) specific external and internal
19、surface area of disperse (e.g. nano-powders) or porous solids by measuring the amount of physically adsorbed gas according to the Brunauer, Emmett and Teller (BET) method (see Reference 1). It takes account of the International Union for Pure and Applied Chemistry (IUPAC) recommendations of 1984 and
20、 1994 (see References 78). NOTE For solids exhibiting a chemically heterogeneous surface, e.g. metal-carrying catalysts, the BET method gives the overall surface area, whereas the metallic portion of the surface area can be measured by chemisorption methods. The BET method is applicable only to adso
21、rption isotherms of type II (disperse, nonporous or macroporous solids) and type IV (mesoporous solids, pore diameter between 2 nm and 50 nm). Inaccessible pores are not detected. The BET method cannot reliably be applied to solids which absorb the measuring gas. A strategy for specific surface area
22、 determination of microporous materials (type I isotherms) is described in Annex C. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of th
23、e referenced document (including any amendments) applies. ISO 8213, Chemical products for industrial use Sampling techniques Solid chemical products in the form of particles varying from powders to coarse lumps ISO 14488, Particulate materials Sampling and sample splitting for the determination of p
24、articulate properties 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 adsorption enrichment of the adsorptive gas at the external and accessible internal surfaces of a solid material ISO 15901-2:2006 2 , 3.4 3.2 physisorption weak bonding of
25、the adsorbate, reversible by small changes in pressure or temperature ISO 15901-3:2007 3 , 3.13 BS ISO 9277:2010 ISO 9277:2010(E) 2 ISO 2010 All rights reserved3.3 adsorbate adsorbed gas ISO 15901-2:2006 2 , 3.1 3.4 adsorptive gas or vapour to be adsorbed ISO 15901-2:2006 2 , 3.5 3.5 adsorbent solid
26、 material on which adsorption occurs ISO 15901-2:2006 2 , 3.3 3.6 isotherm relationship between the amount of gas adsorbed and the equilibrium pressure of the gas, at constant temperature ISO 15901-2:2006 2 , 3.10 3.7 volume adsorbed volumetric equivalent of adsorbed amount expressed as gas at stand
27、ard conditions of temperature and pressure (STP) ISO 15901-2:2006 2 , 3.22 3.8 adsorbed amount quantity of gas adsorbed at a given pressure and temperature NOTE 1 Adsorbed amount is expressed in moles. NOTE 2 Adapted from ISO 15901-3:2007 3 , 3.6. 3.9 monolayer amount number of moles of the adsorbat
28、e that form a monomolecular layer over the surface of the adsorbent ISO 15901-3:2006 3 , 3.8 3.10 surface area extent of available surface area as determined by a given method under stated conditions ISO 15901-1:2006 1 , 3.25 NOTE For the purposes of this International Standard, the area includes th
29、e external surface of a solid plus the internal surface of its accessible macro-, meso- and micropores. 3.11 specific surface area absolute surface area of the sample divided by sample mass BS ISO 9277:2010 ISO 9277:2010(E) ISO 2010 All rights reserved 33.12 molecular cross-sectional area molecular
30、area of the adsorbate, i.e. the area occupied by an adsorbate molecule in the complete monolayer 3.13 macropore pore with width greater than approximately 50 nm NOTE Adapted from ISO 15901-3:2007 3 , 3.10. 3.14 mesopore pore with width between approximately 2 nm and 50 nm ISO 15901-3:2007 3 , 3.11 3
31、.15 micropore pore with width of approximately 2 nm or less NOTE Adapted from ISO 15901-3:2007 3 , 3.12. 3.16 relative pressure ratio of the equilibrium adsorption pressure, p, to the saturation vapour pressure, p 0 , at analysis temperature ISO 15901-3:2007 3 , 3.15 3.17 equilibrium adsorption pres
32、sure pressure of the adsorptive gas in equilibrium with the adsorbate ISO 15901-2:2006 2 , 3.7 3.18 saturation vapour pressure vapour pressure of the bulk liquefied adsorptive gas at the temperature of adsorption ISO 15901-2:2006 2 , 3.20 3.19 free space head space dead space dead volume volume of t
33、he sample holder not occupied by the sample 4 Symbols and abbreviated terms Table 1 presents the symbols used in this International Standard, together with their common units derived from the SI. For comparison purposes, the lUPAC symbols (see References 78) are also given. These may differ from the
34、 symbols generally used in International Standards. All specific dimensions are related to sample mass in grams. BS ISO 9277:2010 ISO 9277:2010(E) 4 ISO 2010 All rights reservedTable 1 Symbols IUPAC symbol Quantity Unit a mmolecular cross-sectional area nm 2a sspecific surface area m 2 g 1C BET para
35、meter 1 aL Avogadro constant (= 6,022 10 23 ) mol 1m mass of the solid sample g m aspecific mass adsorbed 1 an aspecific amount adsorbed mol g 1n mspecific monolayer amount of adsorbate mol g 1n m,mpspecific monolayer amount derived from multipoint measurement mol g 1n m,spspecific monolayer amount
36、derived from single-point measurement mol g 1p pressure of the adsorptive in equilibrium with the adsorbate Pa p 0saturation vapour pressure of the adsorptive Pa p/p 0relative pressure of the adsorptive 1 aR molar gas constant (= 8,314) J mol 1K 1r sradius of uniform nonporous spheres nm t time min
37、T temperature K V aspecific volume adsorbed cm 3 g 1V p,microspecific micropore volume cm 3 g 1 (mass) density g cm 3u ccombined standard uncertainty for the certified specific surface area of a BET reference material m 2g 1k coverage factor for the combined standard uncertainty 1 aU expanded uncert
38、ainty (= k u c ) for the certified specific surface area of a BET reference material m 2 g 1aAccording to ISO 80000-1:2009 4 , 3.8, Note 3, the unit for any quantity of dimension one (at present commonly termed “dimensionless“) is the unit one, symbol 1. 5 Principle The BET method is applicable only
39、 to adsorption isotherms of type II (disperse, nonporous or macroporous solids) and type IV (mesoporous solids, pore diameter between 2 nm and 50 nm) (see Figure 1). Inaccessible pores are not detected. The BET method cannot reliably be applied to solids which absorb the measuring gas. A strategy fo
40、r specific surface area determination of microporous materials (type I isotherms) is described in Annex C. The method specified involves the determination of the amount of adsorbate or adsorptive gas required to cover the external and the accessible internal pore surfaces of a solid (see Figure 2) w
41、ith a complete monolayer of adsorbate. This monolayer amount can be calculated from the adsorption isotherm using the BET equation see Equation (1). Any gas may be used, provided it is physically adsorbed by weak bonds at the surface of the solid (van der Waals forces), and can be desorbed by a decr
42、ease in pressure at the same temperature. BS ISO 9277:2010 ISO 9277:2010(E) ISO 2010 All rights reserved 5Nitrogen at its boiling point (about 77,3 K) is usually the most suitable adsorptive. Very often, argon at liquid argon temperature (i.e. 87,27 K) is a good alternative adsorptive for specific s
43、urface area determination (especially in the case of graphitized carbon and hydroxylated oxide surfaces, see Table A.1, footnote a) because it is a chemically inert monoatomic gas with a symmetrical electron shell configuration quite different from that of nitrogen, although the polarizabilities of
44、argon and nitrogen are remarkably similar. Key n aspecific amount absorbed p/p 0relative pressure Figure 1 IUPAC classification of adsorption isotherms (typical BET range is indicated in types II and IV by the hatched area) Figure 2 Schematic cross-section of a particle with surface detected by the
45、adsorption method shown by dotted line If the sensitivity of the instrument when using nitrogen is insufficient for low specific surface areas of about 1 m 2 g 1or lower, the application of krypton adsorption at liquid nitrogen temperature for the specific surface area analysis is recommended. As a
46、consequence of the low p 0of about 0,35 kPa for krypton at 77,3 K, the “dead space” correction (see 3.19) for unadsorbed gas is significantly reduced (to 1/300th) compared to the conditions of nitrogen adsorption at the same temperature and it becomes possible to volumetrically measure low uptakes o
47、f adsorptive with acceptable accuracy. Although at 77,3 K krypton is about 38,5 K below its triple BS ISO 9277:2010 ISO 9277:2010(E) 6 ISO 2010 All rights reservedpoint temperature, there is some evidence from microcalorimetry and neutron diffraction studies that in the BET region the adsorbate may
48、well be in a liquid-like state and therefore the value of the supercooled liquid is recommended as the effective p 0for the construction of the BET plot. The results of measurements with different adsorptives may deviate from each other because of different molecular areas, different accessibilities
49、 to pores and different measuring temperatures. Moreover, it is well known from the concepts of fractal analysis (Reference 8) that experimental results for the quantities of length and area in the case of irregular complex structures, such as those which are found in most porous or highly dispersed objects, are not absolute, but depend on the measurement scale, i.e. the “yardstick“ used. This means that less area is available for l
