ISO 15901-1:2005

INTERNATIONAL ISO
STANDARD 15901-1
First edition
2005-12-15


Evaluation of pore size distribution and
porosimetry of solid materials by
mercury porosimetry and gas
adsorption —
Part 1:
Mercury porosimetry
Distribution des dimensions des pores et porosimétrie des matériaux
solides par porosimétrie au mercure et par adsorption de gaz —
Partie 1: Porosimétrie au mercure




Reference number
ISO 15901-1:2005(E)
©
ISO 2005

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ISO 15901-1:2005(E)
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ISO 15901-1:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 4
5 Principles. 4
6 Apparatus and material. 5
7 Procedures for calibration and performance. 5
8 Procedures . 6
9 Evaluation. 9
10 Reporting . 10
Annex A (informative) Mercury porosimetry analysis results for alumina reference sample. 12
Bibliography . 18

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ISO 15901-1:2005(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.
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, Sieves, sieving and other sizing methods,
Subcommittee SC 4, Sizing by methods other than sieving.
ISO 15901 consists of the following parts, under the general title Evaluation of pore size distribution and
porosimetry 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 15901-1:2005(E)
Introduction
In general, different pores (micro-, meso-, and macropores) can 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
a given amount of the solid. In addition to the accessible pores, a solid can 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 can 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 of
adsorbent power) 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 of 0,003 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 (2,0 nm to 100 nm), and is an extension of the surface area
estimation technique;
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 2,0 nm, and is an extension of the surface area estimation technique.

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INTERNATIONAL STANDARD ISO 15901-1:2005(E)

Evaluation of pore size distribution and porosimetry 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
[1], [2]
surface in pores of solids by mercury porosimetry according to the method of Ritter 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 psia) corresponding to a minimum equivalent pore diameter of approximately 0,003 µm.
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 interparticle and intraparticle porosity. In general, it cannot
distinguish between these porosities where they co-exist.
The method is suitable for the study of most non-wettable, by mercury, porous materials. 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 can be collapsed and
closed pores opened. In some cases, it is possible to apply sample compressibility corrections and useful
comparative data can still be obtained. 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 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 8213, Chemical products for industrial use — Sampling techniques — Solid chemical products in the form
of particles varying from powders to coarse lumps
M 024 4/85, Quecksilber und seine Verbindungen. Merkblatt der Berufsgenossenschaft der chemischen
Industrie, Postfach 101480, D-69004 Heidelberg, Germany
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ISO 15901-1:2005(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
bulk density
powder density under defined conditions
3.2
blind pore
dead-end-pore
open pore having a single connection with an external surface
3.3
closed pore
cavity not connected to the external surface
NOTE Closed pores are not covered in this International standard.
3.4
contact angle
angle that a non-wetting liquid makes with a solid material
3.5
external surface area
area of external surface including roughness but outside pores
3.6
ink bottle pore
narrow necked open pore
3.7
interconnected pore
pore which communicates with one or more other pores
3.8
internal surface area
area of internal pore walls
3.9
intraparticle porosity
ratio of the volume of open pores internal to the particle to the total volume occupied by the solid
3.10
interparticle porosity
ratio of the volume of space between particles in a powder to the apparent volume of the particles or powder
3.11
macropore
pore of internal width greater than 50 nm
3.12
mesopore
pore of internal width between 2 nm and 50 nm
3.13
micropore
pore of internal width less than 2 nm which is accessible for a molecule to be adsorbed
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ISO 15901-1:2005(E)
3.14
open pore
cavity or channel with access to an external surface
3.15
open porosity
ratio of the volume of open pores and voids to the total volume occupied by the solid
3.16
pore size
pore width (for example, the diameter of a cylindrical pore or the distance between the opposite walls of a slit)
that is a representative value of various sizes of the vacant space inside a porous material
NOTE One of the methods to determine pore sizes is by mercury porosimetry.
3.17
pore volume
volume of pores determined by stated method
3.18
porosimeter
instrument for measuring porosity and pore size distribution
3.19
porosimetry
methods for the estimation of porosity and pore size distribution
3.20
porosity
ratio of total pore volume to apparent volume of particle or powder
3.21
porous solid
solid with cavities or channels which are deeper than they are wide
3.22
skeletal density
mass of a powder divided by the total volume of the sample, including closed pores but excluding open pores
3.23
apparent density
mass of a powder divided by the total volume of the sample, including closed and inaccessible pores, as
determined by the stated method
3.24
powder density
mass of a powder divided by its apparent volume, which is taken to be the total volume of the solid material,
open and closed pores and interstices
3.25
surface area
extent of available surface area as determined by given method under stated conditions
3.26
surface tension
force required to separate a film of liquid from either a solid material or a film of the same liquid
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ISO 15901-1:2005(E)
3.27
through pore
pore which passes all the way through the sample
3.28
total porosity
ratio of the volume of voids plus the volume of open and closed pores to the total volume occupied by the
solid
3.29
true density
true particle density
mass of the particle divided by its volume, excluding open and closed pores
3.30
void
space between particles, i.e. an interparticle pore
4 Symbols
For the purposes of this document, the following symbols apply.
Symbol Term SI unit Derived unit Conversion factors for obsolete
units
-2
p pressure Pa MPa, psia, 1 psia = 1 lb·in = 6 894 Pa
Torr, mm Hg 1 Torr = 1 mm Hg = 133,32 Pa
−9 −6
d pore diameter m nm, µm, Å 1 nm = 10 m, 1 µm = 10 m,

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 3 −6 3
V intruded volume (of mercury) m cm , 10 mm 10 mm = 1 cm = 10 m
Hg

3 3 3 3
V initial intruded volume of mercury m cm , 10 mm —

Hg,0
3 3 3 3
V final intruded volume of mercury m cm , 10 mm —

Hg,max
3 −1 3 3 −1
V specific pore volume m ·kg 10 mm g —

p

−1 −1 −1 −1 −1
γ surface tension of mercury N·m dyne·cm , N·m dyne·cm = N·m
−3 −3 3 −3 3 −3 −3
ρ density of mercury = 13,534 at 25,0 °C kg·m g·cm , 10 kg·m 10 kg·m = 1 g·cm
θ contact angle of mercury at the sample, rad ° 1°= (π/180) rad
measured through the liquid phase
5 Principles
A non-wettable liquid can enter a porous system only when forced by pressure. The pore size distribution of a
porous solid can be determined by forcing mercury into an evacuated sample under increasing pressure and
measuring the volume of mercury intruded as a function of pressure. 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.
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ISO 15901-1:2005(E)
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, 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.
6.2 Porosimeter, 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 operations, 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, of analytical quality, with a purity of at least ratio of 99,4 mass %.
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 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 fills the pores in the
sample. The volume of mercury displaced from a precision glass capillary tube is most commonly determined
as a function of electrical capacity change.
7.2 Pressure signal calibration
Pressure is usually measured with electronic pressure transducers which will have been factory calibrated.
The accuracy of the pressure measurement should be within ± 1 % of the full scale transducer reading or
± 2 % of the actual reading, whichever is the lower. It is recommended that verification of calibration, traceable
to an accredited organisation, be regularly performed.
7.3 Volume signal calibration
The accuracy of the volume measurement should be within ± 1 % of the total volume to be measured. It is
recommended that verification of calibration, traceable to an accredited organisation, be regularly performed.
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ISO 15901-1:2005(E)
7.4 Vacuum transducer calibration
The accuracy of the indicated vacuum is generally not critical. The vacuum manifold system, without a sample,
should be capable of achieving at least 3 Pa, and if possible it should be calibrated to within 1 Pa at this level.
7.5 Verification of porosimeter performance
It is recommended that a certified reference material or a local reference material, selected by the user, must
be tested on a regular basis to monitor instrument calibration and performance. The local reference material
must be traceable to a certified reference material. Certified reference materials are offered by a number of
1) 2)
national standard bodies and are currently available from BAM , in Germany, and NIST , in the USA.
8 Procedures
8.1 Sampling
Sampling should be performed in accordance with ISO 3165. The sample for test should be representative of
the bulk material and should be of an appropriate quantity. Particular precautions should be taken when its
properties are directionally orientated. It is also recommended that a second sample is taken and held in
reserve in case a repeated determination is necessary.
8.1.1 Obtaining a test sample
Since the material from which the sample for test is taken may be in a variety of forms, different subsampling
methods are appropriate as follows.
a) From a block
3
Several pieces about 1 cm may be taken in order to represent different zones from within the block. The
pieces may be cut with a saw or core drill or crushed. There is a possibility that saw or crushing marks can be
interpreted as pores. If coarse pores are of particular interest, polish the surface of the pieces with a medium
of 10 µm maximum particle size. If fine pores are of particular interest, test the sample in the as-sawn
condition and ignore data from pore diameter greater then 125 µm. Polished test pieces should be washed to
remove adhering particles, which can affect the sample mass and block its pores. The sample should be dried
to constant mass. For materials subject to hydration, wash with a non-aqueous liquid.
b) From a powder
Powdery and granular material samples which are free-flowing should be subdivided by rotary sampling or
chute riffling. Non-free-flowing powders may be sampled by coning and quartering. To help distinguish
between inter and intraparticle pores, it can be beneficial to sieve the sample to a particle size range which
allows clearer distinction between the two, but it is important to establish that this does not make the sampling
unrepresentative.
c) From a film or sheet
Film or sheet material may be sampled by either cutting a strip, or by stamping disks, to fit the appropriate
sample holder. Difficulties in testing material in this form can arise due to proximity between adjacent faces.
This can be overcome by rolling steel wire gauze between the faces to keep the surfaces separate.

1) Bundesanstalt für Materialforschung und –prüfung (BAM) Division I. 1 Inorganic Chemical Analysis; Reference
Materials Branch Adlershof, Richard-Willstätter-Straße 11, D-12489 Berlin.
2) Standard Reference Materials Program National Institute of Standards and Technology (NIST) 100 Bureau Drive,
Stop 2322 Gaithersburg, MD 20899-2322.
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ISO 15901-1:2005(E)
8.1.2 Quantity of test sample
The quantity of test sample required is dependent upon its nature. The largest possible sample size
commensurate with the size of cell should be taken. However, the total pore volume should lie within the
recommended measuring range of the capillary tube and the apparatus. In the case of unknown specimens, a
preliminary test will usually be necessary to ascertain the optimum quantity of test sample. The test sample is
3 3
placed preferably in a sample holder having a bulk sample volume between 1 cm and 15 cm ; also larger
cells may be used.
8.2 Method
8.2.1 Sample pretreatment
Sample pretreatment is not required in mercury porosimetry and is often not used. However, pretreatment
does frequently lead to more accurate and repeatable results, especially for samples which are highly
hydrophilic or porous. Evacuation of atmospheric gases at the start of the analysis can proceed more quickly
for samples that have been pretreated due to less evaporation of adsorbed vapours during this evacuation. In
addition, since sample mass is often determined before the sample is placed in the sample holder, pre-treated
samples will yield more reliable masses than those which can be saturated with atmospheric vapours such as
water. Thus, pretreatment removes adsorbed material that can obscure its accessible porosity; this includes
adsorbed water and other materials, such as organic molecules, used in the manufacture or operation of the
porous solid.
In order to optimize pretreatment, it is advisable to study the thermal behaviour of the material, e.g. by
thermogravimetric analysis and differential scanning calorimetry, to determine the temperatures at which
materials are evolved from the sample, together with any phase changes which could affect the history of the
−2
sample. In many cases, heating to 110 °C in a vacuum oven at 3 Pa (2,5 × 10 Torr) for 4 h will be suitable.
However, care should be taken to ensure that the treatment does not affect the porous nature of the sample.
When a satisfactory pretreatment regime has been established, the sample can be out-gassed by heating
and/or evacuation or by flowing inert gas. If the sample is in a form that allows amalgamation with, or wetting
by, mercury, it can be possible to passivate the surface e.g. by producing a thin layer of oxide, or by coating
with a polymer or stearate.
The mass of the test sample to be used should be recorded after any pretreatment.
8.2.2 Filling of the sample holder
After sample pretreatment, the sample should be transferred to a clean and dry sample holder. To minimize
recontamination by, for example, readsorption of water vapour, it is prudent to effect the transfer in a purged
glove box and to dose the sample holder with nitrogen for final transfer to the porosimeter.
8.2.3 Evacuation
The object of sample evacuation is to remove the majority of vapours and gases from the sample, prior to
filling the sample holder with mercury.
Fine powders with relatively high-surface area can tend to fluidize under vacuum with loss of sample into the
vacuum system. This effect can be avoided by selection of sample holders designed specially for powders,
and by controlling the rate of evacuation.
The evacuation vacuum, dependent upon the nature of the material, may be varied. Care should be taken to
[5]
ensure that pore structure does not change due to evacuation, as is possible for some materials . The
evacuation time is considerably reduced for pre-dried samples.
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ISO 15901-1:2005(E)
8.2.4 Filling the sample holder with mercury
A vacuum is required to ensure the transfer of mercury from the reservoir to the sample holder. If the mercury
is de-aerated during filling, this maintains the sample vacuum and avoids air-bubble entrapment.
The hydrostatic pressure of the mercury over the sample under vacuum conditions shall be recorded before
starting the measurement to correct the applied pressure. In vertically filled sample holders, the filling pressure
consists of the applied pressure and the hydrostatic pressure. The hydrostatic pressure may be minimized by
filling the sample holder in a horizontal position, but it shall be taken into account when turning the sample
holder in vertical position. A typical filling pressure would be less than 5 kPa.
8.2.5 Measurement
8.2.5.1 Low pressure
Admit unreacting dry gas (e.g. air, nitrogen or helium) into the evacuated measuring cell in a controlled
manner to increase the pressure either in stages, continuously or by step-wise pressurization according to the
proper equilibration conditions for mercury entering the pores and to a required precision corresponding to the
particular pores sizes of interest. Pressure and corresponding volume of mercury intruded can be recorded
either graphically or via a computer. When the maximum required pressure has been reached, reduce the
pressure to ambient and transfer the sample holder to the high-pressure unit or phase.
8.2.5.2 High pressure
Transfer the sample holder to the high-pressure unit or phase (and mercury can be added if needed) so that it
is possible to dispose to the total length of the capillary. Increase the pressure in the system to the final
pressure reached in the low-pressure phase and record the intrusion volume at this pressure, since
subsequent intrusion volume are calculated from this initial volume. Increase the pressure via the hydraulic
fluid on the mercury, either in stages, continuously (uninterrupted increase in both pressure and time),
stepwise (uniform and regula
...