ISO 12154:2014

Determination of density by volumetric displacement — Skeleton density by gas pycnometry

ISO 12154:2014 specifies a method for rapid and efficient determination of the skeleton density of solid material samples of regular or irregular shape, whether powdered or in one piece, by means of a gas displacement pycnometer.

Détermination de la masse volumique par déplacement volumétrique — Masse volumique du squelette mesurée par pycnométrie à gaz

General Information

• Status: Published
• Publication Date: 18-Mar-2014
• ICS: 19.120 - Particle size analysis. Sieving
• Technical Committee: ISO/TC 24/SC 4 - Particle characterization
• Drafting Committee: ISO/TC 24/SC 4/WG 3 - Pore size distribution, porosity
• Current Stage: 9093 - International Standard confirmed

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 12154
First edition
2014-04-01
Determination of density by
volumetric displacement — Skeleton
density by gas pycnometry
Détermination de la masse volumique par déplacement
volumétrique — Masse volumique du squelette mesurée par
pycnométrie à gaz
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Principle of the method . 2
6 Apparatus and procedure . 3
6.1 Apparatus . 3
6.2 Sample pre-treatment and determination of sample mass . 4
6.3 Determination of the solid skeleton volume of the sample . 5
6.4 Calculation of skeleton density . 6
6.5 Calibration procedure . 6
7 Test report . 8
Annex A (informative) Interferences . 9
Bibliography .11
Foreword
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The committee responsible for this document is ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
iv © ISO 2014 – All rights reserved

Introduction
The true solid state density of a material is defined as the ratio of the mass to the volume occupied by that
mass. Therefore, the contribution to the volume made by pores or internal voids and also interparticle
voids (in the case of granulated or highly dispersed samples) shall be subtracted when calculating the
true density.
If the material has no porosity, the true density can be measured by displacement of any fluid in which
the solid remains inert. The accuracy of the method is limited by the accuracy with which the fluid
volume can be determined. Usually, however, the pores, cracks, or crevices of the material will not easily
be completely penetrated by a displaced liquid. In these instances, the true density can be measured
by using a gas as the displaced fluid if the material does not contain closed pores, which cannot be
penetrated by the analysis gas. Therefore, the density experimentally determined by gas pycnometry
generally is the so called skeleton density of the material which equals the true solid state density only
for samples without closed pores.
Apparatus used to measure solid volumes are often referred to as pyknometers or pycnometers after
the Greek “pyknos”, meaning thick or dense. With gas pycnometry, materials of irregular shape can be
analysed.
Once the volume of solid skeleton of the sample and the sample mass have been determined, the skeleton
density is readily calculated.
INTERNATIONAL STANDARD ISO 12154:2014(E)
Determination of density by volumetric displacement —
Skeleton density by gas pycnometry
1 Scope
This International Standard specifies a method for rapid and efficient determination of the skeleton
density of solid material samples of regular or irregular shape, whether powdered or in one piece, by
means of a gas displacement pycnometer.
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 14488, Particulate materials — Sampling and sample splitting for the determination of particulate
properties
ISO 9277, Determination of the specific surface area of solids by gas adsorption — BET method
ISO 15901-3, Pore size distribution and porosity of solid materials by mercury porosimetry and gas
adsorption — Part 3: Analysis of micropores by gas adsorption
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
density
ratio of the mass of a certain amount of a sample to the volume occupied by that mass
3.2
true solid state density
ratio of the sample mass to the volume of the compact solid skeleton of the sample which excludes the
volume of open and closed pores or internal voids and also interparticle voids as in the case of granulated
or highly dispersed samples
3.3
skeleton density
ratio between sample mass and the 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
3.4
closed pore
pore totally enclosed by its walls and hence not interconnecting with other pores and not accessible to
fluids
3.5
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 fluids
3.6
gauge pressure sensor
because gauge pressure is defined relative to atmospheric conditions, the signal or reading of a gauge
pressure sensor is the total pressure minus atmospheric pressure
3.7
absolute pressure sensor
absolute pressure sensor measures the pressure relative to an absolute vacuum that means the reference
is full vacuum (zero pressure)
4 Symbols and abbreviated terms
Table 1 — Symbols
Symbol Name Unit
-3
ρ skeleton density g cm
s
m sample mass g
s
V skeleton volume of the sample cm
s
V sample chamber volume cm
cell
V reference chamber volume cm
ref
V volume of the calibrated reference sample cm
cal
a
p equilibrated gauge pressure prior to expansion Pa
a
p equilibrated gauge pressure after expansion Pa
a
p equilibrated gauge pressure before expansion (calibration step A) Pa
A1
a
p equilibrated gauge pressure after expansion (calibration step A) Pa
A2
a
p equilibrated gauge pressure before expansion (2nd calibration step) Pa
B1
a
p equilibrated gauge pressure after expansion (2nd calibration step) Pa
B2
p pycnometer pressure at start of analysis Pa
a
∗
pycnometer absolute gas pressure i (i = 1, 2, A1, A2, B1, or B2) Pa
p
i
p pycnometer excess gas pressure i (i = 1, 2, A1, A2, B1, or B2) Pa
i
∗
a
gauge pressure (excess gas pressure) p is defined as the difference between the absolute pressure p and the
i
i
∗
pycnometer pressure p at start of analysis, i.e. pp=−p (see 3.6, 3.7, and 6.3.2.1)
a
ii a
5 Principle of the method
The skeleton density will be determined volumetrically in a gas expansion pycnometer. This technique
is based on the displacement of a volume of gas by the solid space. The measurement is performed by
expanding gas from one chamber to another (see Figure 1) under isothermal conditions. First, the weight
of the dry sample is to be determined and the sample loaded into the sample chamber. The sample
chamber then is pressurized to a set value when using the experimental configuration 1 of Figure 1.
In a further step, the analysis gas will be expanded into a second chamber, the reference volume. The
equilibrated pressures for both steps will be recorded by the instrument. Density is calculated using
these values.
For gas pycnometers according to the experimental configuration 2 of Figure 1, the first step consists in
pressurizing the reference chamber to a set value followed by the expansion into the sample chamber
having a lower initial pressure than the set value. It is important for both experimental pycnometer
configurations, that every chamber of the pycnometer is at the same pressure p prior to starting the
a
2 © ISO 2014 – All rights reserved

analysis steps (see Clause 6) Furthermore, all parts of the pycnometer shall have the same controlled
temperature.
The analysis gas of sufficient purity (see 6.1) shall be nonreactive and also non-adsorbing onto the solid
sample. It has to behave as ideally as possible. Therefore, helium is used for most applications. Another
reason for the preferred use of helium as the analysis gas for gas pycnometry is that it is able to penetrate
even the smallest pores or cracks of a material.
NOTE 1 Because of its pronounced ability to permeate thin inner walls of samples with closed cells, helium can
cause difficulties if permeable samples are to be analysed. Therefore, as described in Annex A.6, gas pycnometric
measurements using helium can be erroneous in the case of organic samples like cellulose and cellular polymers
with low density. For density measurements of those samples, the use of alternative inert gases such as nitrogen,
argon, or sulfur hexafluoride as well as dry air is recommended.
NOTE 2 If the sample contains no closed pores, then the volume measured by gas pycnometry is the true
volume. To test the presence of closed pores, after a first density determination the sample can be powdered
revealing any possible closed pores accessible to the test gas. An increased density value of the ground sample
material indicates closed pores in the original sample.
6 Apparatus and procedure
6.1 Apparatus
[1] [2] [3]
6.1.1 Gas expansion pycnometer, with fixed-volume sample chamber (see Figure 1).
6.1.2 Calibrated reference sample, (in general calibration spheres made of stainless steel with
known traceable volume).
6.1.3 Analysis gas, in general helium (see Clause 5) with a minimum purity of 99,996 % (by volume).
6.1.4 Analytical balance.
6.1.5 Drying oven, for pre-treatment of samples preferably with the option of purging during heating
or heating in a vacuum.
Figure 1 is a schematic diagram of the two principal configurations of automatic gas expansion
pycnometers having fixed sample chamber size. Main components of such instruments are two chambers
connected by tubes (a sample chamber which can be sealed for inserting the sample or the calibration
spheres and a reference chamber), a pressure-measuring sensor, and three valves. The difference
between the pycnometer configurations is in the sequence of the sample chamber and the reference
chamber.
Sample volumes of commercially available gas expansion pycnometers vary from 0,1 cm to about
500 cm . This is accomplished either by having fixed-volume sample chambers of different sizes, or
by means of volume-filling inserts placed into a sample chamber. These variations in sample chamber
volume are necessary because the accuracy of the pycnometric measurement is related to the percent of
total capacity the sample material occupies in the sample chamber.
Configuration 1
Configuration 2
Key
1 valve 1, gas inlet 4 reference chamber
2 valve 2 5 sample chamber
3 valve 3, gas outlet 6 pressure sensor
NOTE The pressure sensor can be either an absolute pressure sensor or a gauge sensor.
Figure 1 — Two principal experimental gas pycnometer configurations
6.2 Sample pre-treatment and determination of sample mass
Preparing the sample is the first step in obtaining accurate results from the pycnometer. Samples shall
be free of moisture in order to obtain true sample mass and to avoid the distorting effect of water vapour
on the volume measurement. The following procedures are recommended, however, modifications may
be necessary for some materials.
Sampling shall be carried out in accordance with ISO 14488. Removing the atmospheric gases from the
sample can be carried out by timed evacuation, timed flow of purge gas, or repetitive pulsing (think
multiple rinses) of purge gas. External oven drying of wet samples is recommended.
Heat sensitive materials can be dried by long-time exposure to silica gel, freeze drying, etc. Materials
having a low melting point can be dried using the purge process. In this case, do not weigh the sample
and cup until after the purge and analysis have been completed.
NOTE Outgassing can be considered complete when the results of duplicate skeleton density analyses are
found within the repeatability limits of the pycnometer used.
4 © ISO 2014 – All rights reserved

It is important to consider that each preparation step should be conducted to avoid
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