ISO 15901-1:2016
(Main)Evaluation of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption — Part 1: Mercury porosimetry
Evaluation of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption — Part 1: Mercury porosimetry
ISO 15901-1:2016 describes a method for the evaluation of the pore size distribution and the specific surface area of pores in solids by mercury porosimetry according to the method of Ritter and Drake[1][2]. It is a comparative test, usually destructive due to mercury contamination, in which the volume of mercury penetrating a pore or void is determined as a function of an applied hydrostatic pressure, which can be related to a pore diameter. Practical considerations presently limit the maximum applied absolute pressure to about 400 MPa (60 000 psi) corresponding to a minimum equivalent pore diameter of approximately 4 nm. The maximum diameter is limited for samples having a significant depth due to the difference in hydrostatic head of mercury from the top to the bottom of the sample. For the most purposes, this limit can be regarded as 400 µm. The measurements cover inter-particle and intra-particle porosity. In general, without additional information from other methods it is difficult to distinguish between these porosities where they co-exist. The method is suitable for the study of most porous materials non-wettable by mercury. Samples that amalgamate with mercury, such as certain metals, e.g. gold, aluminium, copper, nickel and silver, can be unsuitable with this technique or can require a preliminary passivation. Under the applied pressure some materials are deformed, compacted or destroyed, whereby open pores may be collapsed and closed pores opened. In some cases it may be possible to apply sample compressibility corrections and useful comparative data may still be obtainable. For these reasons, the mercury porosimetry technique is considered to be comparative.
Evaluation de la distribution de taille des pores et la porosité des matériaux solides par porosimétrie à mercure et l'adsorption des gaz — Partie 1: Porosimétrie à mercure
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INTERNATIONAL ISO
STANDARD 15901-1
Second edition
2016-04-01
Evaluation of pore size distribution
and porosity of solid materials
by mercury porosimetry and gas
adsorption —
Part 1:
Mercury porosimetry
Evaluation de la distribution de taille des pores et la porosité des
matériaux solides par porosimétrie à mercure et l’adsorption des gaz —
Partie 1: Porosimétrie à mercure
Reference number
ISO 15901-1:2016(E)
©
ISO 2016
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ISO 15901-1:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
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copyright@iso.org
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ii © ISO 2016 – All rights reserved
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ISO 15901-1:2016(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 Principles . 5
6 Apparatus and material . 6
6.1 Sample holder . 6
6.2 Porosimeter . 7
6.3 Mercury . 7
7 Procedures for calibration and performance . 7
7.1 General . 7
7.2 Pressure signal calibration . 7
7.3 Volume signal calibration . 7
7.4 Vacuum transducer calibration . 7
7.5 Verification of porosimeter performance . 8
8 Procedures . 8
8.1 Sampling . 8
8.1.1 Obtaining a test sample . . 8
8.1.2 Quantity of sample . 8
8.2 Method . 9
8.2.1 Sample pre-treatment . 9
8.2.2 Filling of the sample holder and evacuation . 9
8.2.3 Filling the sample holder with mercury . 9
8.2.4 Measurement .10
8.2.5 Completion of test .10
8.2.6 Blank and sample compression correction . .10
9 Evaluation .11
9.1 Determination of the pore size distribution .11
9.2 Determination of the specific pore volume .11
9.3 Determination of the specific surface area .12
9.4 Determination of the bulk and skeleton densities .12
9.5 Determination of the porosity .13
10 Reporting .13
Annex A (informative) Mercury porosimetry analysis results .14
Annex B (informative) Recommendations for the safe handling of mercury .17
Bibliography .19
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ISO 15901-1:2016(E)
Foreword
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 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 matters of
electrotechnical standardization.
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).
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 responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 15901-1:2005), which has been technically
revised. It also incorporates the Corrigendum ISO 15901-1:2005/Cor 1:2007.
ISO 15901 consists of the following parts, under the general title Evaluation of pore size distribution and
porosity of solid materials by mercury porosimetry and gas adsorption:
— Part 1: Mercury porosimetry
— Part 2: Analysis of mesopores and macropores by gas adsorption
— Part 3: Analysis of micropores by gas adsorption
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ISO 15901-1:2016(E)
Introduction
In general, different pores (micro-, meso-, and macropores) may be pictured as either apertures,
channels or cavities within a solid body or as 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 in this International Standard is more precisely defined as the ratio of the total pore
volume of the accessible pores and voids to the volume of the particulate agglomerate. 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 is not covered in this
International Standard.
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 accessible 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 specific surface area.
Porous materials have great technological importance, for example in the context of the following:
— controlled drug release;
— catalysis;
— gas separation;
— filtration including sterilization;
— materials technology;
— environmental protection and pollution control;
— natural reservoir rocks;
— building materials;
— polymers and ceramic.
It is well established that the performance of a porous solid (e.g. its strength, reactivity, permeability) is
dependent on its pore structure. Many different methods have been developed for the characterization
of pore structure. 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. 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.
The most commonly used methods are as follows:
a) Mercury porosimetry, where the pores are filled with mercury under pressure. This method is
suitable for many materials with pores in the approximate diameter range of 0,004 µm to 400 µm.
b) Meso- and macropore analysis by gas adsorption, where the pores are characterized by adsorbing
a gas, such as nitrogen at liquid nitrogen temperature. The method is used for pores in the
approximate diameter range of 0,002 µm to 0,1 µm (2 nm to 100 nm).
c) Micropore analysis by gas adsorption, where the pores are characterized by adsorbing a gas,
such as nitrogen at liquid nitrogen temperature. The method is used for pores in the approximate
diameter range of 0,4 nm to 2 nm.
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INTERNATIONAL STANDARD ISO 15901-1:2016(E)
Evaluation of pore size distribution and porosity of solid
materials by mercury porosimetry and gas adsorption —
Part 1:
Mercury porosimetry
WARNING — The use of this International Standard may involve hazardous materials,
operations and equipment. This International Standard does not purport to address all of the
safety problems associated with its use. It is the responsibility of the user of this International
Standard to establish appropriate safety and health practices and determine the applicability of
regulatory limitations prior to use.
1 Scope
This International Standard describes a method for the evaluation of the pore size distribution and
the specific surface area of pores in solids by mercury porosimetry according to the method of Ritter
[1][2]
and Drake . It is a comparative test, usually destructive due to mercury contamination, in which
the volume of mercury penetrating a pore or void is determined as a function of an applied hydrostatic
pressure, which can be related to a pore diameter.
Practical considerations presently limit the maximum applied absolute pressure to about 400 MPa
(60 000 psi) corresponding to a minimum equivalent pore diameter of approximately 4 nm. The
maximum diameter is limited for samples having a significant depth due to the difference in hydrostatic
head of mercury from the top to the bottom of the sample. For the most purposes, this limit can be
regarded as 400 µm. The measurements cover inter-particle and intra-particle porosity. In general,
without additional information from other methods it is difficult to distinguish between these porosities
where they co-exist. The method is suitable for the study of most porous materials non-wettable by
mercury. Samples that amalgamate with mercury, such as certain metals, e.g. gold, aluminium, copper,
nickel and silver, can be unsuitable with this technique or can require a preliminary passivation. Under
the applied pressure some materials are deformed, compacted or destroyed, whereby open pores may
be collapsed and closed pores opened. In some cases it may be possible to apply sample compressibility
corrections and useful comparative data may still be obtainable. For these reasons, the mercury
porosimetry technique is considered to be comparative.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling
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 definitions apply.
3.1
porosimeter
instrument for measuring pore volume and pore size distribution
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ISO 15901-1:2016(E)
3.2
porosimetry
methods for the estimation of pore volume, pore size distribution, and porosity
3.3
porous solid
solid with cavities or channels which are deeper than they are wide
3.4
powder
porous or nonporous solid composed of discrete particles with maximum dimension less than about
1 mm, powders with a particle size below about 1 µm are often referred to as fine powders
3.5
pore
cavity or channel which is deeper than it is wide, otherwise it is part of the material’s roughness
3.6
void
interstice
space between particles, i.e. interparticle pore
3.7
macropore
pore of internal width greater than 50 nm
3.8
mesopore
pore of internal width between 2 nm and 50 nm
3.9
micropore
pore of internal width less than 2 nm
3.10
closed pore
pore totally enclosed by its walls and hence not interconnecting with other pores and not accessible
to fluids
3.11
open pore
pore not totally enclosed by its walls and open to the surface either directly or by interconnecting with
other pores and therefore accessible to fluid
3.12
ink bottle pore
narrow necked open pore
3.13
pore size
internal pore width (for example, the diameter of a cylindrical pore or the distance between the
opposite walls of a slit) which is a representative value of various sizes of vacant space inside a porous
material
3.14
pore volume
volume of open pores unless otherwise stated
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ISO 15901-1:2016(E)
3.15
pore diameter
diameter of a pore in a model in which the pores typically are assumed to be cylindrical in shape and
which is calculated from data obtained by a specified procedure
3.16
median pore diameter
diameter that corresponds to the 50th percentile of pore volume, i.e. the diameter for which one half of
the pore volume is found to be in larger pores and one half is found to be in smaller pores
3.17
modal pore diameter
mode
pore diameter of the maximum in a differential pore size distribution curve
3.18
hydraulic pore diameter
average pore diameter, calculated as the ratio of pore volume multiplied by four to pore area.
3.19
bulk volume
volume of powder or solids, including all pores (open and closed) and interstitial spaces between
particles.
3.20
bulk density
ratio of sample mass to bulk volume
3.21
skeleton volume
volume of the sample including the volume of closed pores (if present) but excluding the volumes of
open pores as well as that of void spaces between particles within the bulk sample
[SOURCE: ISO 12154]
3.22
skeleton density
ratio of sample mass to skeleton volume
3.23
apparent volume
total volume of the solid constituents of the sample including closed pores and pores inaccessible or not
detectable by the stated method;
3.24
apparent density
ratio of sample mass to apparent volume
3.25
envelope volume
total volume of the particle, including closed and open pores, but excluding void space between the
individual particles
3.26
envelope density
ratio of sample mass to envelope volume
3.27
porosity
ratio of the volume of the accessible pores and voids to the bulk volume occupied by an amount of the solid
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ISO 15901-1:2016(E)
3.28
interparticle porosity
ratio of the volume of void space between the individual particles to the bulk volume of the particles
or powder
3.29
intraparticle porosity
ratio of the volume of open pores inside the individual particles of a particulate or divided solid sample
to the bulk volume occupied by the sample
3.30
surface area
extent of accessible surface area as determined by a given method under stated conditions
3.31
surface tension
work required to increase a surface area divided by that area.
3.32
contact angle
angle at which a liquid/vapour interface meets the surface of a solid material
4 Symbols and abbreviated terms
For the purposes of this document, the following symbols apply.
Symbol Term SI unit Derived and obso- Conversion factors
lete units
6
P pressure Pa MPa, psia, 1 MPa = 10 Pa
−2
Torr, mmHg 1 psi = 1 lb in = 6 895 Pa
1 Torr = 1 mmHg = 133,32 Pa
−9 −6
1nm = 10 m, 1µm = 10 m,
d pore diameter m nm, µm, Å
p
−10
1 Å = 10 m
t time s h 1 h = 3 600 s
2 −1 2 −1
S specific surface area m ·kg m ·g
intruded volume of
3 3 3 3 3 3 −6 3
V m cm , mm 10 mm = 1 cm = 10 m
Hg
mercury
initial intruded volume of
3 3 3
V m cm , mm
Hg,0
mercury
total intruded volume of
3 3 3
V m cm , mm
Hg,max
mercury
3 −1
mm ·g
3 . −1
V specific pore volume m kg
p
3 −1
cm ·g
−1 −1 −1 −3 −1
γ surface tension of mercury N·m dyne·cm 1 dyne·cm = 10 N·m
−3 −3 −3 3 −3
ρ density of mercury kg·m g·cm 1 g·cm = 10 kg·m
Hg
contact angle of mercury at
Θ rad ° 1° = (π/180) rad
the sample
m mass of the test sample kg g
S
m mass of empty sample holder kg g
SH
mass of sample holder with
m kg g
SH+S
sample
mass of sample holder with
m sample and filled with mer- kg g
SH+S+Hg
cury
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ISO 15901-1:2016(E)
Symbol Term SI unit Derived and obso- Conversion factors
lete units
3 3
V bulk volume m cm
B
3 3
V skeleton volume m cm
S
3 3
V volume of sample holder m cm
SH
−3 −3
ρ bulk density kg·m g·cm
B
−3 −3
ρ skeleton density kg·m g·cm
S
ε porosity —
5 Principles
Mercury porosimetry is a widely accepted method for pore size analysis of various materials such as
pharmaceutical tablets, building materials, catalysts and their supports, mainly because it allows pore
size/porosity analysis to be undertaken over a wide range of pore sizes from meso- to macropores with
[1]–[7]
pore widths about 0,004 µm to about 400 µm . In contrast to capillary condensation, where the
pore fluid wets the pore walls (i.e. the contact angle is smaller than 90 degrees), mercury porosimetry
describes a non-wetting situation (i.e. the contact angle is greater than 90 degrees) and therefore
pressure must be applied to force mercury into the pores. Thus, a progressive increase in hydrostatic
pressure is applied to enable the mercury to enter the pores in decreasing order of width. Accordingly,
there is an inverse relationship between the applied pressure, p, and the pore diameter, d , which in the
p
simplest case of cylindrical pores is given by the Washburn equation (see 9.1).
In the application of mercury porosimetry, the volume of mercury entering the pore structure is
measured as the applied pressure is gradually increased. The value V at the applied pressure, p, gives
Hg
the cumulative volume of all available pores of diameter equal to, or greater than, d . The determination
p
may proceed either with the pressure being raised in a step-wise manner and the volume of mercury
intruded measured after an interval of time when equilibrium has been achieved, or by raising the
pressure in a continuous (progressive) manner.
Figure 1 shows two intrusion/extrusion cycles of mercury into a porous powder as a function of
pressure. Region (a) corresponds to a re-arrangement of particles within the powder bed, followed
by intrusion of the interparticle voids (b). Filling of intraparticle pores occurs in the region (c) and
for some materials (reversible) compression is then possible at higher pressures (d). Hysteresis (h)
is observed and extrusion (e) occurs at different pressures than for the intrusion. On completion of a
first intrusion-extrusion cycle, usually some mercury is retained by the sample, thereby preventing the
loop from closing (f). Intrusion-extrusion cycles after the first cycle continue to show hysteresis (g) but
eventually the loop closes, showing that there is no further entrapment of mercury. On most samples,
entrapment is not observed anymore after just the second cycle, which also indicates that hysteresis
and entrapment are essentially of different origin.
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ISO 15901-1:2016(E)
Key
1 powder compression
2 interparticle filling
3 intraparticle filling
Y intruded mercury, V
Hg
X hydraulic pressure, lg p
Figure 1 — Characteristic features of mercury porosimetry curves
The hysteresis and entrapment phenomena is undoubtedly important in order to obtain a comprehensive
pore size analysis. Mercury entrapment appears to be caused by the rupture of mercury bridges in pore
constrictions during extrusion from ink-bottle pores. Different mechanisms have been proposed to
[6]–[12]
explain intrusion/extrusion hysteresis . The single pore mechanism implies that hysteresis can
be understood as an intrinsic property of the intrusion/extrusion process due to nucleation barriers
associated with the formation of a vapour-liquid interface during extrusion, or discussed in terms
of differences in advancing and receding contact angles. In contrast, the network models take into
account the ink-bottle and percolation effects in pore networks. It is now generally accepted that pore
blocking effects, which can occur on the intrusion branch, are similar to the percolation effects involved
in the desorption of gases from porous networks. Indeed, the shape of a mercury intrusion/extrusion
[9][10]
hysteresis loop often agrees well with that of the corresponding gas adsorption loop . Thus,
mercury intrusion and the capillary evaporation appear to be based on similar mechanisms. The
pore blocking/percolation effects are dominant in disordered pore networks, and a reliable pore size
distribution can only be calculated from the intrusion branch by applying complex network models,
based on percolation theory. The application of such models also allows one to obtain a limited amount
[11][12].
of structural information from the intrusion/extrusion hysteresis loop
6 Apparatus and material
WARNING — It is important that proper precautions for the protection of laboratory personnel
are taken when mercury is used. Attention is drawn to the relevant regulations and guidance
documents which appertain for the protection of personnel in each of the member countries.
6.1 Sample holder
The sample holder may consist of a vessel with a uniform bore capillary tube through which the sample
can be evacuated and the vessel filled with mercury. The capillary tube is attached to a wider bore
tube in which the test sample is located. If precise measurements are required, the internal volume of
the capillary tube should be between 20 % and 90 % of the expected pore and interparticle volume of
the sample. Since different materials exhibit a wide range of open porosities a number of sample vessel
holders with different tube diameters and vessel volumes is required. A special design of sample holder
is often used with powdered samples to avoid loss of powder during evacuation.
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ISO 15901-1:2016(E)
In order to evaluate the porosity and the bulk and skeleton densities, the volume of the sample holder,
including the capillary tube, must be known.
6.2 Porosimeter
An instrument capable of carrying out the test at two sequential measurements, a low pressure test
up to at least 0,2 MPa (30 psi) and a high-pressure test up to the maximum operating pressure of the
porosimeter [circa 400 MPa (60 000 psi)].
The porosimeter may have several ports for high and low pressure operation, or the low pressure test
may be carried out on a separate unit.
Prior to any porosimetry measurement it is necessary to evacuate the sample using a typical rotary
vacuum pump, equipped with a mercury retainer and then to fill the sample holder with mercury to a
given low pressure. A means of generating pressure is necessary to cause intrusion of mercury.
3
A means of detecting the change in the volume of mercury intruded to a resolution of 1 mm or less is
desirable. This is usually done by measuring the change in capacitance between the mercury column in
the capillary tube and a metal sleeve around the outside of the sample holder.
6.3 Mercury
Mercury in analytical quality should be used for the measurements (at least a mass ratio of 99,5 %
[17]
purity ).
7 Procedures for calibration and performance
7.1 General
Sample preparation and the filling of the sample holder with mercury require a vacuum, the level of
which is usually recorded using a transducer. For the porosity evaluation, two signals are required to
be measured in a porosimeter; the applied pressure and the corresponding volume change of mercury
as it intrudes into the pores in the sample. The volume of mercury displaced from
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 15901-1
ISO/TC 24/SC 4 Secretariat: DIN
Voting begins on: Voting terminates on:
2013-12-16 2014-03-16
Evaluation of pore size distribution and porosity of solid
materials by mercury porosimetry and gas adsorption —
Part 1:
Mercury porosimetry
Distribution de taille des pores et la porosité des matériaux solides par porosimétrie à mercure et
l’adsorption des gaz —
Partie 1: Porosimétrie à mercure
[Revision of first edition (ISO 15901-1:2005) and ISO 15901-1:2005/Cor 1:2007]
ICS: 19.120
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 15901-1:2013(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2013
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ISO/DIS 15901-1:2013(E)
Copyright notice
This ISO document is a Draft International Standard and is copyright-protected by ISO. Except as
permitted under the applicable laws of the user’s country, neither this ISO draft nor any extract
from it may be reproduced, stored in a retrieval system or transmitted in any form or by any means,
electronic, photocopying, recording or otherwise, without prior written permission being secured.
Requests for permission to reproduce should be addressed to either ISO at the address below or ISO’s
member body in the country of the requester.
ISO copyright office
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ii © ISO 2013 – All rights reserved
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ISO/DIS 15901-1
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 5
5 Principles. 6
6 Apparatus and material . 7
6.1 Sample holder . 7
6.2 Porosimeter . 7
6.3 Mercury . 7
7 Procedures for calibration and performance . 7
7.1 General . 7
7.2 Pressure signal calibration. 8
7.3 Volume signal calibration . 8
7.4 Vacuum transducer calibration . 8
7.5 Verification of porosimeter performance . 8
8 Procedures . 8
8.1 Sampling. 8
8.1.1 Obtaining a test sample . 8
8.1.2 Quantity of sample . 9
8.2 Method . 9
8.2.1 Sample pre-treatment . 9
8.2.2 Filling of the sample holder . 9
8.2.3 Evacuation . 10
8.2.4 Filling the sample holder with mercury . 10
8.2.5 Measurement . 10
8.2.6 Completion of test . 11
8.2.7 Blank and sample compression correction . 11
9 Evaluation. 11
9.1 Determination of the pore size distribution . 11
9.2 Determination of the specific pore volume . 12
9.3 Determination of the specific surface area . 12
9.4 Determination of the bulk and skeleton densities . 13
9.4.1 Bulk density . 13
9.4.2 Skeleton density . 13
9.5 Determination of the porosity . 13
10 Reporting . 14
Annex A (informative) Mercury porosimetry analysis results . 15
A.1 Presentation of pore size distributions (Example) . 15
A.2 Intrusion data summary (Example) . 15
Annex B (informative) Recommendations for the safe handling of mercury . 18
Bibliography . 19
© ISO 2013 – All rights reserved iii
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ISO/DIS 15901-1
Foreword
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 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 matters 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 circulated 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 responsible for identifying any or all such patent rights.
ISO 15901-1 was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
ISO 15901 consists of the following parts, under the general title Evaluation of pore size distribution and
porosity of solid materials by mercury porosimetry and gas adsorption:
Part 1: Mercury porosimetry
Part 2: Analysis of mesopores and macro-pores by gas adsorption
Part 3: Analysis of micropores by gas adsorption
iv © ISO 2013 – All rights reserved
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ISO/DIS 15901-1
Introduction
In general, different pores (micro-, meso-, and macropores) may be pictured as either apertures, channels or
cavities within a solid body or as 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 the accessible pores and voids to the total volume occupied by
an amount of the solid. 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 is not covered in this standard.
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 specific surface area.
Porous materials have great technological importance, for example in the context of the following:
controlled drug release,
catalysis,
gas separation,
filtration including sterilization,
materials technology,
environmental protection and pollution control,
natural reservoir rocks,
building materials properties,
polymers and ceramic.
It is well established that the performance of a porous solid (e.g. its strength, reactivity, permeability) is
dependent on its pore structure. Many different methods have been developed for the characterization of pore
structure. 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. 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.
The most commonly used methods are as follows:
a) mercury porosimetry, where the pores are filled with mercury under pressure. This method is suitable for
many materials with pores in the appropriate diameter range of 0,004 µm to 400 µm.
b) meso- and macropore analysis by gas adsorption, where the pores are characterized by adsorbing a gas,
such as nitrogen, at liquid nitrogen temperature. The method is used for pores in the approximate
diameter range of 0,002 µm to 0,1 µm (2 nm to 100 nm).
c) micropore analysis by gas adsorption, where the pores are characterized by adsorbing a gas, such as
nitrogen, at liquid nitrogen temperature. The method is used for pores in the approximate diameter range
of 0,4 nm to 2 nm.
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DRAFT INTERNATIONAL STANDARD ISO/DIS 15901-1
Evaluation of pore size distribution and porosity of solid
materials by mercury porosimetry and gas adsorption — Part 1:
Mercury porosimetry
WARNING — The use of this International Standard may involve hazardous materials, operations and
equipment. This International Standard does not purport to address all of the safety problems
associated with its use. It is the responsibility of the user of this International Standard to establish
appropriate safety and health practices and determine the applicability of regulatory limitations prior
to use.
1 Scope
This international standard describes a method for the evaluation of the pore size distribution and the specific
surface area of pores in solids by mercury porosimetry according to the method of Ritter and Drake [1] [2]. It is
a comparative test, usually destructive due to mercury contamination, in which the volume of mercury
penetrating a pore or void is determined as a function of an applied hydrostatic pressure, which can be related
to a pore diameter.
Practical considerations presently limit the maximum applied absolute pressure to about 400 MPa
(60 000 psia) corresponding to a minimum equivalent pore diameter of approximately 4 nm. The maximum
diameter will be limited for samples having a significant depth due to the difference in hydrostatic head of
mercury from the top to the bottom of the sample. For the most purposes, this limit can be regarded as
400 µm. The measurements cover inter-particle and intra-particle porosity. In general, without additional
information from other methods it is difficult to distinguish between these porosities where they co-exist. The
method is suitable for the study of most porous materials non-wettable by mercury. Samples that amalgamate
with mercury, such as certain metals, e.g. gold, aluminium, reduced copper, reduced nickel and silver, can be
unsuitable for this technique or can require a preliminary passivation. Under the applied pressure some
materials are deformed, compacted or destroyed, whereby open pores may be collapsed and closed pores
opened. In some cases it may be possible to apply sample compressibility corrections and useful comparative
data may still be obtainable. For these reasons, the mercury porosimetry technique is considered to be
comparative.
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 the referenced
document (including any amendments) applies.
ISO 14488, Particulate materials — Sampling and sample splitting for the determination of particulate
properties
ISO 8213, Chemical products for industrial use — Sampling techniques — Solid chemical products in the form
of particles varying from powders to coarse lumps
JIS K 8572, Mercury
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ISO/DIS 15901-1
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
porosimeter
instrument for measuring pore volume and pore size distribution
3.2
porosimetry
methods for the estimation of pore volume, pore size distribution, and porosity
3.3
porous solid
solid with cavities or channels which are deeper than they are wide
3.4
powder
porous or nonporous solid composed of discrete particles with maximum dimension less than about 1 mm,
powders with a particle size below about 1 µm are often referred to as fine powders
3.5
pore
pores in solid materials are cavities or channels which are deeper than they are wide otherwise they are part
of material's roughness
3.6
void/interstice
space between particles, i.e. interparticle pore
3.7
macropore
pore of internal width greater than 50 nm
3.8
mesopore
pore of internal width between 2 nm and 50 nm
3.9
micropore
pore of internal width less than 2 nm
3.10
closed pore
a pore totally enclosed by its walls and hence not interconnecting with other pores and not accessible to fluids
Note 1 to entry: Pores with apertures smaller than approx. 4 nm are not accessible to mercury porosimetry, and
therefore considered closed pores in this standard.
3.11
open pore
a pore not totally enclosed by its walls and open to the surface either directly or by interconnecting with other
pores and therefore accessible to fluid
3.12
ink bottle pore
narrow necked open pore
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ISO/DIS 15901-1
3.13
pore size
internal pore width (for example the diameter of a cylindrical pore or the distance between the opposite walls
of a slit) which is a representative value of various sizes of vacant space inside a porous material
3.14
pore volume
volume of open pores unless otherwise stated
3.15
pore diameter
diameter of a pore in a model in which the pores typically are assumed to be cylindrical in shape and which is
calculated from data obtained by a specified procedure
3.16
median pore diameter
diameter that corresponds to the 50th percentile of pore volume, i.e. the diameter for which one half of the
pore volume is found to be in larger pores and one half is found to be in smaller pores
3.17
modal pore diameter (mode)
pore diameter of the maximum in a pore size distribution curve
3.18
hydraulic pore diameter
average pore diameter, calculated as the ratio of pore volume multiplied by four to pore area
3.19
bulk volume
volume of powder or solids, including all pores (open and closed) and interstitial spaces between particles
Note 1 to entry: For mercury porosimetry: volume of the sample plus pores not filled by mercury at the applied
pressure of interest, generally that at the start of the analysis or filling of the sample holder with mercury.
3.20
bulk density
ratio of sample mass to bulk volume
3.21
skeleton volume
volume of the sample including the volume of closed pores (if present) but excluding the volumes of open
pores as well as that of void spaces between particles within the bulk sample (ISO 12154)
Note 1 to entry: Open pores with apertures smaller than approx. 4 nm are not accessible to mercury porosimetry, and
therefore if such pores are present, a skeleton volume cannot be determined but rather an apparent volume is assessed.
3.22
skeleton density
ratio of sample mass to skeleton volume
3.23
apparent volume
total volume of the solid constituents of the sample including closed pores and pores inaccessible or not
detectable by the stated method
Note 1 to entry: In mercury porosimetry the accessibility of pores is a function of applied pressure.
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ISO/DIS 15901-1
3.24
apparent density
mass of a material divided by the apparent volume
3.25
envelope volume
total volume of the particle, including closed and open pores, but excluding void space between the individual
particles
3.26
envelope density
ratio of the mass of a particle to the envelope volume of the particle
3.27
porosity
ratio of the volume of the accessible pores and voids to the bulk volume occupied by an amount of the solid
3.28
interparticle porosity
ratio of the volume of void space between the individual particles to the bulk volume of the particles or powder
3.29
intraparticle porosity
ratio of the volume of open pores inside the individual particles of a particulate or divided solid sample to the
bulk volume occupied by the sample
3.30
surface area
extent of available surface area as determined by given method under stated conditions
3.31
surface tension
work required to increase a surface area divided by that area
3.32
contact angle
angle at which a liquid/vapour interface meets the surface of a solid material
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ISO/DIS 15901-1
4 Symbols and abbreviated terms
For the purposes of this document, the following symbols apply.
Derived and
Symbol Term SI unit Conversion factors
obsolete units
6
1 MPa = 10 Pa
MPa, psia,
–2
p Pressure Pa
1 psia = 1 lb in = 6 895 Pa
Torr, mmHg
1 Torr = 1 mm Hg = 133,32 Pa
–9 –6
1 nm = 10 m, 1 µm = 10 m,
d
pore diameter m nm, µm, Å
p
–10
1 Å = 10 m
t Time s h
1 h = 3 600 s
2 –1 2 –1
S
specific surface area m ·kg m ·g
3 3 3 3 3 3 –6 3
V
intruded volume of mercury m cm , mm 10 mm = 1 cm = 10 m
Hg
3 3 3
V
initial intruded volume of mercury m cm , mm
Hg,0
3 3 3
V
total intruded volume of mercury
m cm , mm
Hg,max
3 –1
mm ·g
3 –1
V
specific pore volume m kg
p
3 –1
cm ·g
–1 –1 –1 –3 –1
surface tension of mercury
γ N·m dyne·cm 1 dyne·cm = 10 N·m
–3 –3 –3 3 –3
ρ
density of mercury kg·m g·cm 1 g·cm = 10 kg·m
Hg
contact angle of mercury at the
rad °
θ 1° = (π/180) rad
sample
m
mass of the test sample kg g
S
m
mass of empty sample holder kg g
SH
mass of sample holder with
m
kg g
SH+S
sample
mass of sample holder with
m
kg g
SH+S+Hg
sample and filled with mercury
3 3
V
Bulk Volume m cm
B
3 3
V
Skeleton Volume m cm
S
3 3
V
Volume of sample holder
m cm
SH
–3 –3
ρ
Bulk density kg·m g·cm
B
–3 –3
ρ
Skeleton density
kg·m g·cm
S
P Porosity —
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ISO/DIS 15901-1
5 Principles
Mercury porosimetry is a widely accepted method for pore size analysis of various materials such as
pharmaceutical tablets, building materials, catalysts and their supports, mainly because it allows pore
size/porosity analysis to be undertaken over a wide range of mesopore-macropore widths (routinely, from
circa 0,004 µm to ca. 400 µm) [1]-[7]. In contrast to capillary condensation, where the pore fluid wets the pore
walls (i.e. the contact angle < 90 degrees), mercury porosimetry describes a non-wetting situation (contact
angle > 90 degrees) and therefore pressure must be applied to force mercury into the pores. Thus, a
progressive increase in hydrostatic pressure is applied to enable the mercury to enter the pores in decreasing
order of width. Accordingly, there is an inverse relationship between the applied pressure p and the pore
diameter which in the simplest case of cylindrical pores is given by the Washburn equation (see section 9.1).
In the application of mercury porosimetry, the volume of mercury entering the pore structure is measured as
the applied pressure is gradually increased. The value V at the applied pressure p gives the cumulative
Hg,0
volume of all available pores of diameter equal to, or greater than, d . The determination may proceed either
p
with the pressure being raised in a step-wise manner and the volume of mercury intruded measured after an
interval of time when equilibrium has been achieved, or by raising the pressure in a continuous (progressive)
manner.
Figure 1 shows two intrusion/extrusion cycles of mercury into a porous powder as a function of pressure.
Region (a) corresponds to a re-arrangement of particles within the powder bed, followed by intrusion of the
interparticle voids (b). Filling of pores occurs in the region (c) and for some materials (reversible) compression
is then possible at higher pressures (d). Hysteresis (h) is observed and extrusion (e) occurs at different
pressures than for the intrusion. On completion of a first intrusion-extrusion cycle, usually some mercury is
retained by the sample, thereby preventing the loop from closing (f). Intrusion-extrusion cycles after the first
cycle continue to show hysteresis (g) but eventually the loop closes, showing that there is no further
entrapment of mercury. On most samples, entrapment is not observed anymore after just the second cycle,
which also indicates that hysteresis and entrapment are essentially of different origin.
Figure 1 — Characteristic features of mercury porosimetry curves
An understanding of the hysteresis and entrapment phenomena is most important in order to obtain a
comprehensive pore size analysis. Mercury entrapment appears to be caused by the rupture of mercury
bridges in pore constrictions during extrusion leading to mercury entrapment in ink-bottle pores. Different
mechanisms have been proposed to explain intrusion/extrusion hysteresis [6]-[11]. The single pore
mechanism implies that hysteresis can be understood as an intrinsic property of the intrusion/extrusion
process due to nucleation barriers associated with the formation of a vapour-liquid interface during extrusion,
or is discussed in terms of differences in advancing and receding contact angles. In contrast, the network
models take into account the ink-bottle and percolation effects in pore networks. It is now generally accepted
that pore blocking effects, which can occur on the intrusion branch, are similar to the percolation effects
involved in the desorption of gases from porous networks. Indeed, the shape of a mercury intrusion/extrusion
hysteresis loop often agrees quite well with that of the corresponding gas adsorption loop [9]. Thus, mercury
intrusion and the capillary evaporation appear to be based on the same mechanism. The pore
blocking/percolation effects are dominant in disordered pore networks, and a reliable pore size distribution can
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ISO/DIS 15901-1
only be calculated from the intrusion branch by applying complex network models based on percolation
theory. The application of such models also allows one to obtain a limited amount of structural information
from the intrusion/extrusion hysteresis loop [10], [11].
6 Apparatus and material
WARNING –– It is important that proper precautions for the protection of laboratory personnel are
taken when mercury is used. Attention is drawn to the relevant regulations and guidance documents
which appertain for the protection of personnel in each of the member countries.
6.1 Sample holder
Vessel having a uniform bore capillary tube through which the sample can be evacuated and through which
mercury can enter. The capillary tube is attached to a wider bore tube in which the test sample is located. If
precise measurements are required the internal volume of the capillary tube should be between 20 % and
90 % of the expected pore and void volume of the sample. Since different materials exhibit a wide range of
open porosities a number of sample holders with different diameter capillary tubes and sample volumes may
be required. A special design of sample holder is often used with powdered samples to avoid loss of powder
during evacuation.
In order to evaluate the porosity and the bulk and skeletal densities the volume of the sample holder, including
the capillary tube, must be exactly known.
6.2 Porosimeter
Instrument capable of carrying out the test as two sequential measurements, a low pressure test up to at least
0,2 MPa (30 psia) and a high-pressure test up to the maximum operating pressure of the porosimeter [circa
400 MPa (60 000 psia)].
The porosimeter may have several ports for high and low pressure operation, or the low pressure test may be
carried out on a separate unit
Prior to any porosimetry measurement it is necessary to evacuate the sample using a vacuum pump,
equipped with mercury retainer, to a residual pressure of 7 Pa or less and then to fill the sample holder with
mercury to a given low pressure. A means of generating pressure is necessary to cause intrusion of mercury.
3
A means of detecting the change in the volume of mercury intruded to a resolution of 1 mm or less is
desirable. This is usually done by measuring the change in capacitance between the mercury column in the
capillary tube and a metal sleeve around the outside of the sample holder.
6.3 Mercury
Mercury in an analytical quality should be used for the measurements (at least a mass ratio of 99,5 % purity
according to JIS K 8572).
7 Procedures for calibration and performance
7.1 General
Sample preparation and the filling of the sample holder with mercury require vacuum, the level of which is
usually recorded using a trans
...
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