DIN ISO 9277-2014 Determination of the specific surface area of solids by gas adsorption - BET method (ISO 9277 2010)《用气体吸附法进行固体表面积测定 BET法(ISO 9277-2010)》.pdf

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1、January 2014Translation by DIN-Sprachendienst.English price group 14No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS

2、 19.120!%+9A“2082230www.din.deDDIN ISO 9277Determination of the specific surface area of solids by gas adsorption BET method (ISO 9277:2010),English translation of DIN ISO 9277:2014-01Bestimmung der spezifischen Oberflche von Festkrpern mittels Gasadsorption BET-Verfahren (ISO 9277:2010),Englische b

3、ersetzung von DIN ISO 9277:2014-01Dtermination de laire massique (surface spcifique) des solides par adsorption de gaz Mthode BET (ISO 9277:2010),Traduction anglaise de DIN ISO 9277:2014-01SupersedesDIN ISO 9277:2003-05www.beuth.deIn case of doubt, the German-language original shall be considered au

4、thoritative.Document comprises 28 pages01.14 A comma is used as the decimal marker. Contents Page National foreword .3 National Annex NA (informative) Explanatory notes 4 1 Scope .5 2 Normative references .5 3 Terms and definitions 5 4 Symbols and abbreviated terms .7 5 Principle .8 6 Procedure . 10

5、 6.1 Sample preparation . 10 6.2 Experimental conditions . 13 6.3 Measuring methods for the assessment of the amount of adsorbed gas . 13 7 Evaluation of adsorption data 16 7.1 General . 16 7.2 Multipoint determination . 16 7.3 Single-point determination . 18 8 Test report 18 9 Use of reference mate

6、rials 19 Annex A (informative) Cross-sectional areas of some frequently used adsorptives . 20 Annex B (informative) Certified reference materials for the BET method . 21 Annex C (informative) Surface area of microporous materials 23 Bibliography . 27 DIN ISO 9277:2014-012National foreword This docum

7、ent (ISO 9277:2010-09) has been prepared by Technical Committee ISO/TC 24 “Particle char-acterization including sieving”, Subcommittee SC 4 “Particle characterization”. The secretariat is currently held by BSI (United Kingdom). The responsible German body involved in its preparation was the Normenau

8、sschuss Bauwesen (Building and Civil Engineering Standards Committee), Working Committee NA 005-11-43 AA Partikelmesstechnik, Porosi-tts- und Oberflchenmessverfahren (SpA zu ISO/TC 24/SC 4/WG 3). Attention is drawn to the possibility that some of the elements of this document may be the subject of p

9、atent rights. DIN and/or DKE shall not be held responsible for identifying any or all such patent rights. Amendments This standard differs from DIN ISO 9277:2003-05 as follows: a) the standard has been technically and editorially revised as well as extended; b) Annexes A and B have been restructured

10、; further cross-sectional areas of frequently used adsorptives have been added and the list of currently available certified BET reference materials and their supply sources has been updated; c) Annex C “Surface area of microporous materials” has been added and, among others, provides informa-tion o

11、n how the BET method can be used with these materials. It should be noted that this standard includes three national footnotes. Previous editions DIN 66131: 1973-10, 1993-07 DIN ISO 9277: 2003-05 DIN ISO 9277:2014-013National Annex NA (informative) Explanatory notes When using the gravimetric method

12、 to measure the adsorption isotherm, knowledge of the volumes of the balance relevant to buoyancy (sample holder, suspension, balance beam), the solid volume of the sample, and the density of the measuring gas at the relevant adsorption pressure are needed to calculate the buoyancy correction of the

13、 balance. The sum of the volumes of the balance relevant to buoyancy and the solid volume of the sample can be determined simultaneously by means of a gas pressure-dependent buoyancy measurement with the sample in place, carried out at the same temperature and within the same pressure range as the g

14、ravimetric adsorption measurement, using a gas that is non-adsorbing under these conditions (e.g. nitrogen, helium or argon). As an alternative, the volumes of the balance relevant to buoyancy can also be determined on the basis of a buoyancy measurement carried out without the sample in place. In t

15、his case, the solid volume of the sample is to be calculated on the basis of its mass and solid density. If the solid density of the sample is unknown, it is to be determined in accordance with DIN 66137-2. If no non-adsorbing gas for the relevant measuring temperature is available, the buoyancy mea

16、surement is to be carried out either at a higher temperature with the sample in place, or carried out without the sample, with the solid volume of the sample then being determined separately. Details on buoyancy correction are given in DIN 66136-4 and DIN 66138. DIN ISO 9277:2014-014Determination of

17、 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 surface area of disperse (e.g. nano-powders) or porous solids by measuring the amount of physically adsorbed gas

18、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 1994 (see References 78). NOTE For solids exhibiting a chemically heterogeneous surface, e.g. metal-carrying cat

19、alysts, 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 adsorption isotherms of type II (disperse, nonporous or macroporous solids) and type IV (mesoporous solids, pore diam

20、eter 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 determination of microporous materials (type I isotherms) is described in Annex C. 2 Normative references The fo

21、llowing 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 the referenced document (including any amendments) applies. ISO 8213, Chemical products for industrial use Sampling

22、 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 particulate properties 3 Terms and definitions For the purposes of this document, the following terms and definiti

23、ons apply. 3.1 adsorption enrichment of the adsorptive gas at the external and accessible internal surfaces of a solid material ISO 15901-2:20062, 3.4 3.2 physisorption weak bonding of the adsorbate, reversible by small changes in pressure or temperature ISO 15901-3:20073, 3.13 3.3 adsorbate adsorbe

24、d gas ISO 15901-2:20062, 3.1 DIN ISO 9277:2014-0153.4 adsorptive gas or vapour to be adsorbed ISO 15901-2:20062, 3.5 3.5 adsorbent solid material on which adsorption occurs ISO 15901-2:20062, 3.3 3.6 isotherm relationship between the amount of gas adsorbed and the equilibrium pressure of the gas, at

25、 constant temperature ISO 15901-2:20062, 3.10 3.7 volume adsorbed volumetric equivalent of adsorbed amount expressed as gas at standard conditions of temperature and pressure (STP) ISO 15901-2:20062, 3.22 3.8 adsorbed amount quantity of gas adsorbed at a given pressure and temperature NOTE 1 Adsorbe

26、d amount is expressed in moles. NOTE 2 Adapted from ISO 15901-3:20073, 3.6. 3.9 monolayer amount number of moles of the adsorbate that form a monomolecular layer over the surface of the adsorbent ISO 15901-3:20063, 3.8 3.10 surface area extent of available surface area as determined by a given metho

27、d under stated conditions ISO 15901-1:20061, 3.25 NOTE For the purposes of this International Standard, the area includes the 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 b

28、y sample mass N1) National footnote: STP is an internationally established abbreviation for “standard temperature and pressure”, for the conditions T = 273,15 K and p = 101 325 Pa. N1) DIN ISO 9277:2014-0163.12 molecular cross-sectional area molecular area of the adsorbate, i.e. the area occupied by

29、 an adsorbate molecule in the complete monolayer 3.13 macropore pore with width greater than approximately 50 nm NOTE Adapted from ISO 15901-3:20073, 3.10. 3.14 mesopore pore with width between approximately 2 nm and 50 nm ISO 15901-3:20073, 3.11 3.15 micropore pore with width of approximately 2 nm

30、or less NOTE Adapted from ISO 15901-3:20073, 3.12. 3.16 relative pressure ratio of the equilibrium adsorption pressure, p, to the saturation vapour pressure, p0, at analysis temperature ISO 15901-3:20073, 3.15 3.17 equilibrium adsorption pressure pressure of the adsorptive gas in equilibrium with th

31、e adsorbate ISO 15901-2:20062, 3.7 3.18 saturation vapour pressure vapour pressure of the bulk liquefied adsorptive gas at the temperature of adsorption ISO 15901-2:20062, 3.20 3.19 free space head space dead space dead volume volume of the sample holder not occupied by the sample 4 Symbols and abbr

32、eviated 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 symbols generally used in International Standards. All specif

33、ic dimensions are related to sample mass in grams. N2) National footnote: In the German version of this standard, the terms “free space”, “head space”, “dead space” and “dead volume” are called Totvolumen. N2) DIN ISO 9277:2014-017Table 1 Symbols IUPAC symbol Quantity Unit ammolecular cross-sectiona

34、l area nm2asspecific surface area m2 g1C BET parameter 1aL Avogadro constant (= 6,022 1023) mol1m mass of the solid sample g maspecific mass adsorbed 1anaspecific amount adsorbed mol g1nmspecific monolayer amount of adsorbate mol g1nm,mpspecific monolayer amount derived from multipoint measurement m

35、ol g1nm,spspecific monolayer amount derived from single-point measurement mol g1p pressure of the adsorptive in equilibrium with the adsorbate Pa p0saturation vapour pressure of the adsorptive Pa p/p0relative pressure of the adsorptive 1aR molar gas constant (= 8,314) J mol1K1rsradius of uniform non

36、porous spheres nm t time min T temperature K Vaspecific volume adsorbed cm3 g1Vp,microspecific micropore volume cm3 g1 (mass) density g cm3uccombined standard uncertainty for the certified specific surface area of a BET reference material m2g1k coverage factor for the combined standard uncertainty 1

37、aU expanded uncertainty (= k uc) for the certified specific surface area of a BET reference material m2 g1aAccording to ISO 80000-1:20094, 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 app

38、licable only 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

39、 strategy for 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

40、 Figure 2) with 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 desorb

41、ed by a decrease in pressure at the same temperature. DIN ISO 9277:2014-018Nitrogen 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 surface area determination (espe

42、cially 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 argon and nitrogen are remarkab

43、ly similar. Key naspecific amount absorbed p/p0relative 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 adsorption method shown by dotted

44、 line If the sensitivity of the instrument when using nitrogen is insufficient for low specific surface areas of about 1 m2 g1or lower, the application of krypton adsorption at liquid nitrogen temperature for the specific surface area analysis is recommended. As a consequence of the low p0of about 0

45、,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 of adsorptive with acceptable accurac

46、y. Although at 77,3 K krypton is about 38,5 K below its triple DIN ISO 9277:2014-019point temperature, there is some evidence from microcalorimetry and neutron diffraction studies that in the BET region the adsorbate may well be in a liquid-like state and therefore the value of the supercooled liqui

47、d is recommended as the effective p0for 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 to pores and different measuring temperatures. Moreover, it is well known from

48、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 “yards

49、tick“ used. This means that less area is available for larger adsorbate molecules. The adsorptive gas is admitted to the sample container which is held at a constant temperature. The amounts adsorbed are measured in equilibrium with the adsorptive gas pressure p and plotted against relative pressure, p/p0, to give an adsorption isotherm. Adsorption isotherms may be obtained by volumetric, grav