ISO 15901-2:2022

INTERNATIONAL ISO
STANDARD 15901-2
Second edition
2022-01
Pore size distribution and porosity
of solid materials by mercury
porosimetry and gas adsorption —
Part 2:
Analysis of nanopores by gas
adsorption
Distribution des dimensions des pores et porosité des matériaux
solides par porosimétrie au mercure et par adsorption de gaz —
Partie 2: Analyse des nanopores par adsorption de gaz
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 3
5 Principles . 4
5.1 General . 4
5.2 Methods of measurement . 8
5.3 Choice of adsorptive . 9
6 Measurement procedure .10
6.1 Sampling . 10
6.2 Sample pretreatment . 10
6.3 Measurement . 10
7 Verification of apparatus performance .10
8 Calibration .11
9 Pore size analysis .11
9.1 General . 11
9.2 Classical, macroscopic, thermodynamic methods for pore size analysis .12
9.2.1 Assessment of microporosity .12
9.2.2 Assessment of meso/macroporosity . 19
9.3 Advanced, microscopic approaches based on density functional theory and
molecular simulation . 20
9.3.1 General .20
9.3.2 Application for pore size analysis: Kernel and integral adsorption equation .20
10 Reporting .21
Annex A (informative) Horvath-Kawazoe and Saito-Foley method .22
Annex B (informative) NLDFT method .25
Bibliography .28
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces ISO 15901-2:2006 and ISO 15901-3:2007, which have been
technically revised. It also incorporates the Technical Corrigendum ISO 15901-2:2006/Cor.1:2007.
The main changes compared to the previous edition are as follows:
— the analysis of nanopores by gas adsorption which combines the characterization of both micro-
and mesopores is now addressed;
— the classification of adsorption isotherms and hysteresis loops has been updated.
A list of all parts in the ISO 15901 series can be found on the ISO website.
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.
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Introduction
In general, different types of pores may be pictured as apertures, channels, or cavities within a solid
body or as the space (i.e. interstices or voids) between solid particles in a bed, compact or aggregate.
Porosity is a term which is often used to indicate the porous nature of solid material and is more
precisely defined as the ratio of the volume of accessible pores and voids to the total volume occupied
[1]
by a given amount of the solid. According to the 2015 IUPAC recommendations , nanopores are defined
as pores with internal widths of equal or less than 100 nm and are divided into several subgroups
dependent on their pore width:
— pores with width greater than about 50 nm are called macropores;
— pores of widths between 2 nm and 50 nm are called mesopores;
— pores with width of about 2 nm and less are called micropores;
Further, IUPAC suggested a subclassification of micropores into supermicropores (pore width 0,7 nm
to 2 nm), and ultramicropores (pore width < 0,7 nm). In addition to the accessible pores, a solid may
contain closed pores which are isolated from the external surface and into which fluids are not able to
penetrate. The characterization of closed pores, i.e. cavities with no access to an external surface, is not
covered in this document.
Porous materials may take the form of fine or coarse powders, compacts, extrudates, sheets or
monoliths. Their characterization usually involves the determination of the pore size distribution as
well as the total pore volume or porosity. For some purposes it is also necessary to study the pore shape
and interconnectivity, and to determine the internal and external surface area.
Porous materials have great technological importance, e.g. in the context of the following:
a) controlled drug release;
b) catalysis;
c) gas separation;
d) filtration including sterilization;
e) materials technology;
f) environmental protection and pollution control;
g) natural reservoir rocks;
h) building material properties;
i) polymer and ceramic industries.
It is well established that the performance of a porous solid (e.g. its strength, reactivity, permeability
or adsorbent power) is dependent on its pore structure. Many different methods have been developed
for the characterization of pore structure. The choice of the most appropriate method depends on the
application of the porous solid, its chemical and physical nature and the range of pore size.
Different methods for the characterization of nanopores are available, including spectroscopy, electron
and tunnel microscopy and sorption methods. In view of the complexity of most porous solids, it is not
surprising that the results obtained are not always in agreement and that no single technique can be
relied upon to provide a complete picture of the pore structure. Among these, mercury porosimetry (see
ISO 15901-1) and gas adsorption are popular ones because by combining both it is possible to assess a
wide range of pore sizes from below 0,5 nm up to 400 µm. While mercury porosimetry is the standard
technique for macropore analysis, gas adsorption techniques allow to assess pores up to approximately
100 nm. In this case, physical adsorption can be conveniently used, is not destructive, and is not that
cost intensive as compared to some of the above-mentioned methods. Particularly, with regard to the
v
application of microporous material as specific sorbents, molecular sieves and carriers for catalysts
and biological active material, the field-proven methods of gas sorption are of special value.
The measuring techniques of the method described in this document are similar to those described in
ISO 9277 for the measurement of gas adsorption at low temperature. However, in order to assess the
full range of pore sizes including microporosity, adsorption experiments have to be performed over a
wide range of pressures from the ultralow pressure range (e.g. turbomolecular pump vacuum) up to
atmospheric pressure (0,1 MPa).
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INTERNATIONAL STANDARD ISO 15901-2:2022(E)
Pore size distribution and porosity of solid materials by
mercury porosimetry and gas adsorption —
Part 2:
Analysis of nanopores by gas adsorption
1 Scope
This document describes a method for the evaluation of porosity and pore size distribution by physical
adsorption (or physisorption). The method is limited to the determination of the quantity of a gas
[1]-[9]
adsorbed per unit mass of sample as a function of pressure at a controlled, constant temperature .
Commonly used adsorptive gases for physical adsorption characterization include nitrogen, argon,
krypton at the temperatures of liquid nitrogen and argon (77 K and 87 K respectively) as well as CO (at
273 K). Traditionally, nitrogen and argon adsorption at 77 K and 87 K, respectively, allows one to assess
pores in the approximate range of widths 0
...