Evaluation of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption

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

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Status
Published
Publication Date
03-Apr-2016
Current Stage
9020 - International Standard under periodical review
Start Date
15-Apr-2021
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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
---------------------- Page: 1 ----------------------
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

the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
---------------------- Page: 2 ----------------------
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

© ISO 2016 – All rights reserved iii
---------------------- Page: 3 ----------------------
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
iv © ISO 2016 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO 2016 – All rights reserved v
---------------------- Page: 5 ----------------------
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
© ISO 2016 – All rights reserved 1
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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
2 © ISO 2016 – All rights reserved
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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

© ISO 2016 – All rights reserved 3
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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
P pressure Pa MPa, psia, 1 MPa = 10 Pa
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
−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
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
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
contact angle of mercury at
Θ rad ° 1° = (π/180) rad
the sample
m mass of the test sample kg g
m mass of empty sample holder kg g
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
4 © ISO 2016 – All rights reserved
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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
3 3
V skeleton volume m cm
3 3
V volume of sample holder m cm
−3 −3
ρ bulk density kg·m g·cm
−3 −3
ρ skeleton density kg·m g·cm
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

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

the cumulative volume of all available pores of diameter equal to, or greater than, d . The determination

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.
© ISO 2016 – All rights reserved 5
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ISO 15901-1:2016(E)
Key
1 powder compression
2 interparticle filling
3 intraparticle filling
Y intruded mercury, V
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.
6 © ISO 2016 – All rights reserved
---------------------- Page: 11 ----------------------
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.

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
---------------------- Page: 1 ----------------------
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
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Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ii © ISO 2013 – All rights reserved
---------------------- Page: 2 ----------------------
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

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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
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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
1 MPa = 10 Pa
MPa, psia,
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,
pore diameter m nm, µm, Å
–10
1 Å = 10 m
t Time s h
1 h = 3 600 s
2 –1 2 –1
specific surface area m ·kg m ·g
3 3 3 3 3 3 –6 3
intruded volume of mercury m cm , mm 10 mm = 1 cm = 10 m
3 3 3
initial intruded volume of mercury m cm , mm
Hg,0
3 3 3
total intruded volume of mercury
m cm , mm
Hg,max
3 –1
mm ·g
3 –1
specific pore volume m kg
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
density of mercury kg·m g·cm 1 g·cm = 10 kg·m
contact angle of mercury at the
rad °
θ 1° = (π/180) rad
sample
mass of the test sample kg g
mass of empty sample holder kg g
mass of sample holder with
kg g
SH+S
sample
mass of sample holder with
kg g
SH+S+Hg
sample and filled with mercury
3 3
Bulk Volume m cm
3 3
Skeleton Volume m cm
3 3
Volume of sample holder
m cm
–3 –3
Bulk density kg·m g·cm
–3 –3
Skeleton density
kg·m g·cm
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

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.

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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