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4 Symbols
5 Principle
6 Procedure
6.1 Sample preparation
6.2 Experimental conditions
6.3 Measuring methods for the assessment of the amount of adsorbed gas
6.3.1 General
6.3.2 Static manometric (volumetric) method
6.3.3 Flow manometric (volumetric) method
6.3.4 Gravimetric method
6.3.5 Carrier gas method
6.3.6 Dynamic vapour sorption method
7 Evaluation of adsorption data
7.1 General
7.2 Multipoint determination
7.3 Single-point determination
8 Test report
9 Use of reference materials
Annex A (informative) Cross-sectional areas of some frequently used adsorptives
Annex B (informative) BET area of microporous materials
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International Standard ISO 9277 | |
Determination of the specific surface area of solids by gas adsorption — BET method Détermination de l'aire massique (surface spécifique) des solides par adsorption de gaz — Méthode BET Reference number ISO 9277:2022(en) | Third edition 2022-11
© ISO 2022
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COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.
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ContentsPage
4 Symbols
5 Principle
6 Procedure
6.1 Sample preparation
6.2 Experimental conditions
6.3 Measuring methods for the assessment of the amount of adsorbed gas
6.3.1 General
6.3.2 Static manometric (volumetric) method
6.3.3 Flow manometric (volumetric) method
6.3.4 Gravimetric method
6.3.5 Carrier gas method
6.3.6 Dynamic vapour sorption method
7 Evaluation of adsorption data
7.1 General
7.2 Multipoint determination
7.3 Single-point determination
8 Test report
9 Use of reference materials
Annex A (informative) Cross-sectional areas of some frequently used adsorptives
Annex B (informative) BET area of microporous materials
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving, Subcommittee SC 4, Particle characterization.
This third edition cancels and replaces the second edition (ISO 9277:2010), which has been technically revised.
The main changes compared to the previous edition are as follows:
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the IUPAC classification of adsorption isotherms has been updated according to Reference [3];
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the description of dynamic vapour sorption (DVS) method in 6.3.6 has been added;
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Annex A has been revised;
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Annex B has been removed;
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the former Annex C (now Annex B) has been revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.
Introduction
Gas adsorption allows for assessing surface area of nonporous materials and porous materials with accessible porosity (which depends on the chosen adsorptive) via the Brunauer, Emmett and Teller (BET) theory[1],[2]. The BET theory is applicable only to adsorption isotherms of type II (disperse, nonporous or macroporous solids) and type IV (mesoporous solids) (see Figure 1, Type II and Type IVa isotherms). However, in the case of Type IVb isotherms, caution is required since pore condensation can occur at quite low p/p0 (see IUPAC recommendations[3]). The BET method cannot reliably be applied to solids which absorb the measuring gas. A strategy for BET area determination of microporous materials (type I isotherms) is described in Annex B.
Figure 1 — IUPAC (2015) classification of adsorption isotherms | |||||||
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fig_1
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1Scope
This document specifies the determination of the overall specific external and internal surface area of either disperse (e.g. nano-powders) or porous, solids by measuring the amount of physically adsorbed gas according to the method of Brunauer, Emmett and Teller method,[1] based on the 2015 International Union for Pure and Applied Chemistry (IUPAC) recommendations[3].
NOTEFor solids exhibiting a chemically heterogeneous surface, for example, metal-carrying catalyst, the BET method gives the overall surface area, whereas the metallic portion of the surface area can be measured by chemisorption methods.
2Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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 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
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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ISO Online browsing platform: available at https://www.iso.org/obp
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IEC Electropedia: available at https://www.electropedia.org/
3.1
adsorption
enrichment of the adsorptive gas at the external and accessible internal surfaces of a solid material
3.2
physisorption
weak bonding of the adsorbate (3.2), reversible by small changes in pressure or temperature
3.3
adsorbate
adsorbed gas
3.4
adsorptive
gas or vapour to be adsorbed
3.5
adsorbent
solid material on which adsorption (3.1) occurs
3.6
isotherm
relationship between the amount of gas adsorbed and the equilibrium pressure of the gas, at constant temperature
3.7
volume adsorbed
volumetric equivalent of adsorbed amount (3.8) expressed as gas at standard conditions of temperature and pressure (STP)
3.8
adsorbed amount
number of moles of gas adsorbed at a given pressure and temperature
3.9
monolayer capacity
volumetric equivalent of monolayer amount expressed as gas at standard conditions of temperature and pressure
3.10
surface area
area of the external surface of a solid plus the internal surface of its accessible macro-, meso- and micropores (3.16)
3.11
specific surface area
absolute surface area (3.10) of the sample divided by sample mass
3.12
molecular cross-sectional area
molecular area of the adsorbate (3.2), i.e. the area occupied by an adsorbate molecule in the complete monolayer
3.13
nanopore
pore with width of about 100 nm or less
3.14
macropore
pore with width greater than approximately 50 nm
3.15
mesopore
pore with width between approximately 2 nm and 50 nm
3.16
micropore
pore with width of approximately 2 nm or less
3.17
3.18
saturation vapour pressure
vapour pressure of the bulk liquefied adsorptive gas at the temperature of adsorption (3.1)
3.19
free space
head space
dead space
dead volume
volume of the sample holder not occupied by the sample
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Bibliography
[1] | Brunauer S., Emmett P.H., & Teller E. Adsorption of gases in multimolecular layers, J. Am. Chem. Soc. 60, 1938, pp. 309-319 | |
[2] | Rouquerol J., Avnir D., Fairbridge C.W., Everett D.H., Haynes J.H., Pernicone N., Ramsay J.D.F., Sing K.S.W., & Unger K.K. Recommendations for the Characterization of Porous Solids (IUPAC Recommendations 1994). Pure Appl. Chem. 66, 1994, pp. 1739-1758 | |
[3] | Thommes M, Kaneko K., Neimark A.V., & Olivier J. Rodriguez-Reinoso F., Rouquerol J., Sing K.S.W., Physisorption of Gases, with Special Reference to the Evaluation of Surface Area and Pore Size Distribution (IUPAC Technical Report), Pure & Appl. Chem. 87, 2015, pp. 1051-1069 | |
[4] | Frisch B., & Röper M. Theorie der Strömungsmethode bei der Messung spezifischer Oberflächen und Mikroporositäten. Kolloid-Z. Z. Polym. 223, 1967, pp. 150-160 | |
[5] | Brunauer S., Skalny J., & Bodor E.E. Adsorption on nonporous solids. J. Colloid Interface Sci. 30, 1969, pp. 546-552 | |
[6] | Straube B. Kritische Untersuchung und Standardisierung physikalisch-chemischer Meßmethoden zur Ermittlung der spezifischen Oberfläche und Porenverteilung von Adsorbentien. Dissertation, Universität Mainz, 1985 | |
[7] | McClellan A.L., & Harnsberger H.F. Cross-sectional areas of molecules adsorbed on solid surfaces. J. Colloid Interface Sci. 23, 1967, pp. 577-599 | |
[8] | Gregg S.J., & Sing K.S.W. Adsorption, Surface Area and Porosity. Academic Press, London, 2nd edn., 1982. | |
[9] | Mikhail R.S., & Robens E. Microstructure and Thermal Analysis of Solid Surfaces. Wiley, Chichester, 1983 | |
[10] | Rouquerol F., Rouquerol J., & Sing K.S.W. Adsorption by Powders and Porous Solids. Academic Press, San Diego London Boston New York Sydney Tokyo Toronto, 1999 | |
[11] | Lowell, S., Shields, J.E., Thomas, M.A. and Thommes, M.: Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density. Kluwer Academic Publishers, Dortrecht Boston London, 2004 | |
[12] | Dąbrowski A., Robens E., Klobes P., Meyer K., & Podkościelny P. Standardization of Methods for Characterizing the Surface Geometry of Solids. Particle & Particle Systems Characterization 20, 2003, pp. 311-322 | |
[13] | ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) | |
[14] | Aguado J., Serrano D.P., Escola J.M., & Rodrigues J.M. Low temperature synthesis and properties of ZSM-5 aggregates formed by ultra-small nanocrystals. Micropor. Mesopor. Mat. 75, 2004, pp. 41-49 | |
[15] | Rouquerol J., Llewellyn P., & Rouquerol F. Is the BET equation applicable to microporous adsorbents? In: Characterisation of porous solids VII. Lewellyn, P., Rodriguez-Reinoso, F., Rouquerol, J., Seaton, N. (Eds): Studies in Surface Science and Catalysis, 160, 2007, pp. 49-56 | |
[16] | Schneider P. Adsorption isotherms of microporous-mesoporous solids revisited. Applied Catalysis A, General 129, 1995, pp. 157-165 | |
[17] | Jelinek L., & Kovats E.S. True Surface Areas from Nitrogen Adsorption Experiments. Langmuir 10, 1994, pp. 4225-4231 | |
[18] | Galarneau A., Desplantier D., Dutartre R., & Di Renzo F. Micelle-templated silicates as a test bed for methods of mesopore size evaluation. Micropor. Mesopor. Mat. 27,1999, pp. 297-308 | |
[19] | Rouquerol J., Rouquerol F., Peres C., Grillet Y., & Boudellal M. Adsorption on Porous Silicas. In: Characterisation of Porous Solids, Gregg S.J., Sing K.S.W., & Stoeckli H.F. (Eds), Soc. Chem. Ind., London, 1979, pp. 107-116 | |
[20] | ||
[21] | ISO 80000-1, Quantities and units — Part 1: General | |
[22] | ISO 15901-2, Pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption — Part 2: Analysis of nanopores by gas adsorption |
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