ISO 26824:2022

INTERNATIONAL ISO
STANDARD 26824
Second edition
2022-08
Particle characterization of particulate
systems — Vocabulary
Caractérisation des particules dans les systèmes particulaires —
Vocabulaire
Reference number
ISO 26824:2022(E)
© ISO 2022

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ISO 26824:2022(E)
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 26824:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to representation of size and classification analysis data . 1
3.2 Terms related to representation of particle shape . 9
3.3 Terms related to pore size distribution, porosity and surface area analysis . 11
3.4 Terms related to gravity or centrifugal sedimentation methods . 17
3.5 Terms related to electrical sensing zone methods . 21
3.6 Terms related to laser diffraction methods . 21
3.7 Terms related to dynamic light scattering . 25
3.8 Terms related to image analysis methods . 26
3.9 Terms related to single particle light interaction methods .30
3.10 Terms related to small angle X-ray scattering . 32
3.11 Terms related to sample preparation and reference materials . 33
3.12 Terms related to electrical mobility and number concentration analysis for
aerosol particles . 35
3.13 Terms related to electrical charge conditioning .39
3.14 Terms related to acoustic methods . 41
3.15 Terms related to focused beam method .44
3.16 Terms related to characterisation of particle dispersion in liquids .44
3.17 Terms related to methods for zeta potential determination . 47
Bibliography .54
Index .55
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ISO 26824:2022(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 of the voluntary nature of standards, 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
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 26824:2013), which has been technically
revised.
The main changes are as follows:
— All definition clauses have been rearranged as subclauses in Clause 3 and all terms and clauses have
been renumbered.
— Latest revisions and documents from ISO/TC 24/SC 4 have been incorporated, as well as
harmonization with ISO/TC 229 general definitions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 26824:2022(E)
Introduction
Since the last revision of this document in 2013, about 24 ISO standards have been published by
ISO/TC 24/SC 4 and about 15 projects are currently under construction together with the 5-year
revision of the existing standards. Therefore, terms and definitions of each standard, which are relevant
for other standards should be collected and adjusted to a uniform nomenclature.
Especially the interdisciplinary application fields of particle and particulate systems characterization
- from mining and construction industry, pharmaceutical and food industry, medicine and life sciences,
chemical industry, microelectronics and nanotechnology - need transparency and unambiguous
terminology. The development of international trade not only of measurement devices for particle
characterization, but also of process equipment for the production and treatment of particulate systems
need the comparability of quality and performance parameters as well as international health, safety
and environmental protection regulations.
The structuring and presentation rules applied to the terminological entries are based on a clause
structure, which represents the methods of sample preparation, measurement results presentation and
the analysis methods, starting with more general terms in each clause.
The clause headlines address "Terms related to" technical fields, which are understood as a kind of
domain with validity of the definitions limited to the indicated field.
The following particle properties are covered in the clauses given in brackets:
— particle size (3.1, 3.4 to 3.10, 3.12 to 3.15)
— particle shape (3.2, 3.8)
— particle number concentration (3.5, 3.9 and 3.12)
— pore size, pore volume (3.3)
— surface area (3.3, 3.10)
— electrical charge in aerosols (3.13)
— zeta potential in liquid dispersion (3.17)
— particle dispersion in liquids (3.16).
Data uncertainty related definitions are given in 3.1 and 3.11
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INTERNATIONAL STANDARD ISO 26824:2022(E)
Particle characterization of particulate systems —
Vocabulary
1 Scope
This document defines terms that are relevant to the characterization of particles and particulate
systems. This document includes such fields as the representation of results of particle size analysis,
the descriptive and quantitative representation of particle shape and morphology, sample preparation,
specific surface area and porosity characterization and such measurement methods as sedimentation,
classification, acoustic methods, laser diffraction, dynamic light scattering, single particle light
interaction methods, differential electrical mobility analysis, image analysis and others in a size scale
from nanometre to millimetre.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms related to representation of size and classification analysis data
3.1.1
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary can also be described as an interface.
Note 2 to entry: A particle can move as a unit.
Note 3 to entry: This general particle definition applies to nano-objects (3.1.7).
[SOURCE: ISO 26824:2013, 1.1]
3.1.2
agglomerate
collection of weakly or medium strongly bound particles (3.1.1) where the resulting external surface
area is similar to the sum of the surface areas of the individual components
Note 1 to entry: The forces holding an agglomerate together are weak forces, for example van der Waals forces or
simple physical entanglement.
Note 2 to entry: Agglomerates are also termed secondary particles and the original source particles are termed
primary particles (3.1.4).
[SOURCE: ISO 26824:2013, 1.2]
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ISO 26824:2022(E)
3.1.3
aggregate
particle (3.1.1) comprising strongly bonded or fused particles where the resulting external surface area
is significantly smaller than the sum of surface areas of the individual components
Note 1 to entry: The forces holding an aggregate together are strong forces, for example covalent bonds, or those
resulting from sintering or complex physical entanglement or otherwise combined former primary particles
(3.1.4).
Note 2 to entry: Aggregates are also termed secondary particles and the original source particles are termed
primary particles (3.1.4).
[SOURCE: ISO 26824:2013, 1.3]
3.1.4
primary particle
original source particle (3.1.1) of agglomerates (3.1.2) or aggregates (3.1.3) or mixtures of the two
Note 1 to entry: Constituent particles (3.1.5) of agglomerates (3.1.2) or aggregates (3.1.3) at a certain actual state
can be primary particles, but often the constituents are aggregates.
Note 2 to entry: Agglomerates (3.1.2) and aggregates (3.1.3) are also termed secondary particles.
[SOURCE: ISO 26824:2013, 1.4]
3.1.5
constituent particle
identifiable, integral component of a larger particle (3.1.1)
Note 1 to entry: The constituent particle structures may be primary particles (3.1.4) or aggregates (3.1.3).
Note 2 to entry: See Figure 1.
Note 3 to entry: Constituent particles are considered as the smallest dispersible units of a large particle.
Key
1 agglomerate - constituent particles are identical to primary particles
2 aggregate with covalent bond - constituent particles are identical to primary particles
3 aggregate, produced from initially formed, primary particles (of approximetly 10 or more times smaller size
than the widths of the aggregate) which coalesce during the pyrogenic process and sinter into long chains (the
visible large circle-like parts never existed as isolated particles before)
4 example of an agglomerate, formed from aggregates (key 3), which are the constituent particles-
Figure 1 — Examples for agglomerates and aggregates of constituent particles and primary
particles (not identifiable as such in all cases)
[SOURCE: ISO/TS 80004-2:2015, 3.3, modified — Figure 1 has been added, Note 1 has been modified,
Note 2 and 3 have been added]
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ISO 26824:2022(E)
3.1.6
nanoscale
length range approximately from 1 nm to 100 nm
Note 1 to entry: Properties that are not extrapolations from larger sizes are predominantly exhibited in this
length range.
[SOURCE: ISO/TS 80004-1:2015, 2.1]
3.1.7
nano-object
discrete piece of material with one, two or three external dimensions in the nanoscale (3.1.6)
Note 1 to entry: The second and third external dimensions are orthogonal to the first dimension and to each
other.
[SOURCE: ISO/TS 80004-1:2015, 2.5]
3.1.8
nanomaterial
material with any external dimension in the nanoscale (3.1.6) or having internal structure or surface
structure in the nanoscale
[SOURCE: ISO/TS 80004-1:2015, 2.4]
3.1.9
particle size
x
d
linear dimension of a particle (3.1.1) determined by a specified measurement method and under
specified measurement conditions
Note 1 to entry: Different methods of analysis are based on the measurement of different physical properties.
Independent of the particle property actually measured, the particle size is reported as a linear dimension, e.g. as
the equivalent spherical diameter (3.1.10).
Note 2 to entry: Examples of size descriptors are those based at the opening of a sieve or a statistical diameter,
e.g. the Feret diameter, measured by image analysis.
Note 3 to entry: In ISO 9276 the symbol ‘x’ is used to denote the particle size. However, it is recognised that
the symbol ‘d’ is also widely used to designate these values. Therefore the symbol ‘x’ may be replaced by ‘d’.
[ISO 9276-1:1998, 3.1]
[SOURCE: ISO 9276-1:1998, 4.2, modified – text reformated]
3.1.10
equivalent diameter
equivalent spherical diameter
diameter of a sphere that produces a response by a given particle-sizing method, that is equivalent to
the response produced by the particle (3.1.1) being measured
Note 1 to entry: The physical property to which the equivalent diameter refers is indicated using a suitable
subscript [ISO 9276-1:1998].
Note 2 to entry: For discrete-particle-counting, light-scattering instruments, an equivalent optical diameter is
used.
Note 3 to entry: Other material constants like density of the particle are used for the calculation of the equivalent
diameter like Stokes diameter or sedimentation equivalent diameter. The material constants, used for the
calculation, should be reported additionally.
Note 4 to entry: For inertial instruments, the aerodynamic diameter is used. Aerodynamic diameter is the
−3
diameter of a sphere of density 1 000 kg m that has the same settling velocity as the irregular particle.
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ISO 26824:2022(E)
[SOURCE: ISO/TS 80004-6:2021, 4.1.5]
3.1.11
type of quantity
r
specification of the quantity of a distribution, a cumulative (3.1.13) or a density measure (3.1.14).
Note 1 to entry: The type is indicated by the general subscript, r, or by the appropriate value of r as follows:
number: r = 0
length: r = 1
area: r = 2
volume or mass: r = 3
[SOURCE: ISO 9276-1:1998, 4.3]
3.1.12
particle size distribution
distribution of particles (3.1.1) as a function of particle size (3.1.9)
Note 1 to entry: Particle size distribution may be expressed as cumulative distribution (3.1.13) or a distribution
density (3.1.14) (distribution of the fraction of material in a size class, divided by the width of that class).
[SOURCE: ISO/TS 80004-6:2013, 3.1.2]
3.1.13
cumulative distribution
Q (x)
r
distribution of the fraction of material smaller (undersize) than given particle sizes (3.1.9)
Note 1 to entry: If the cumulative distribution, Q (x), is calculated from histogram data, only individual points
r
Q = Q (x ) are obtained. Each individual point of the distribution, Q (x ), defines the relative amount of particles
r,i r i r i
smaller than or equal to x . The continuous curve is calculated by suitable interpolation algorithms. The
i
normalized cumulative distribution extends between 0 and 1, i.e. 0 and 100 %.
i i
QQ==ΔΔq x with 1 ≤ v ≤ i ≤ n.
r,iv∑ r, ∑ r,v v
v=1 v=1
where
i (subscript) number of the size class with upper limit x
i
ν (integer, see subscript i)
n total number of size classes
Q relative amount of particles in size class with upper limit x
r,ν ν
Note 2 to entry: When plotted on a graph paper with a logarithmic abscissa the cumulative values, Q , i.e. the
r,i
ordinates of a cumulative distribution, do not change. However, the course of the cumulative distribution curve
changes but the relative amounts smaller than a certain particle size remain the same. Therefore, the following
equation holds:
Q (x) = Q (In x)
r r
Note 3 to entry: The cumulative oversize distribution is given by 1−Q (x).
r
[SOURCE: ISO 9276-1:1998, 5.2]
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ISO 26824:2022(E)
3.1.14
distribution density
q (x)
r
distribution of the fraction of material in a size class, divided by the width of that class
Note 1 to entry: Under the presupposition that the cumulative distribution (3.1.13), Q (x), is differentiable, the
r
continuous distribution density, q (x), is obtained from
r
dQx
()
r
qx()=
r
dx
Conversely, the cumulative distribution (3.1.13), Q (x), is obtained from the distribution density, q (x), by
r r
integration:
x
i
Qx = qx dx
() ()
ri r
∫
x
min
Note 2 to entry: The more common term “density distribution” can be misunderstood in the context of
sedimentation methods, so an alternative has been adopted.
Note 3 to entry: Differential distribution is also called in statistics "density of a probability or frequency"
[SOURCE: ISO 9276-1:1998, 5.3, modified – “density distribution” replaced with “distribution density”]
3.1.15
distribution density on a logarithmic abscissa
q* (x)
r
distribution density (3.1.14), transformed for a logarithmic abscissa
Note 1 to entry: The density values of a histogram, q* = ‾ q* (x , x ), can be recalculated using the following
r,i r i-1 i
equation which indicates that the corresponding areas underneath the distribution density curve remain
constant. In particular, the total area is equal to 1 or 100 %, independent of any transformation of the abscissa.
∗
qq()ξξ,,ΔΔξ = ()xx x where ξ is any function of x.
ri−−11ii ri ii
Thus the following transformation can be carried out to obtain the distribution density on a logarithmic abscissa
qxΔ ΔQ
qx(),xxΔ
ri, i ri,
∗ ∗ ri−1 ii
qx()=⋅qx or qx()ln ,lnx = = =
rrii,i ri−1 i
lnxx−ln ln xx/ ln xx/
() ()
ii−−1 ii 111ii−
Note 2 to entry: This equation also holds if the natural logarithm is replaced by the logarithm to base 10.
[SOURCE: ISO 9276-1:1998, 6.2]
3.1.16
histogram
graphical representation of a distribution density q (x) (3.1.14), comprising a successive series of
r
rectangular columns with the height of mean distribution density, qx() , and the width of Δx , the
ri, i
area of each represents the relative quantity ΔQ (x), where
r,i
ΔQ
ΔQx(),x
ri,
ri−−1 i
ΔΔQQ= xx,,=qx xxΔ or qq= xx, = =
() () ()
ri,,ri−−11ir ii ri ri−1 i
Δx Δx
i i
Note 1 to entry: The sum of all the relative quantities, ΔQ forms the area beneath the histogram q (x), normalized
r,i r
to 100 % or 1 (condition of normalization). Therefore, following equation holds:
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ISO 26824:2022(E)
n n
ΔΔQq==x 1= 100 %
∑∑ri,,ri i
i==11i
[SOURCE: ISO 9276-1:1998, 5.1]
3.1.17
concentration distribution density
distribution of the concentration of material in a size class, divided by the width of that class
Note 1 to entry: In aerosol measurement e. g. the distribution density of the particle number concentration is
represented as a function of the particle size.
Note 2 to entry: The concentration distribution density can be calculated from the distribution density (3.1.14)
function of the particle size (3.1.9) by multiplication with the overall sizes measured concentration.
3.1.18
analytical cut size
x
a
cut size with the coarse and the fine material containing equal quantities of misplaced material
Note 1 to entry: Since the relative mass of the fine material as determined by the classification process, is taken
to be equal to the relative mass of the undersize material in the feed, that is Q (x), an analytical cut size x
3,s
corresponding to this definition has to be found.
[SOURCE: ISO 9276-4:2001, 4.3.2]
3.1.19
equiprobable cut size
x
e
cut size, which represents the median of the grade efficiency (3.1.20) curve T(x ) = 0,5
e
Note 1 to entry: The weighted distribution density curves of the fine and the coarse fraction intersect at the
equiprobable cut size x . Independently from other particle sizes (3.1.9), particles of this size have the equal
e
probability to be classified into the fine and into the coarse fraction.
[SOURCE: ISO 9276-4:2001, 3.3.2]
3.1.20
grade efficiency
T(x)
grade efficiency (Tromp's curve, Partial classification efficiency) represents for a certain particle size
(3.1.9) x the ratio of the amount of material present in the coarse material, to the amount of the same
size initially present in the feed material.
[SOURCE: ISO 9276-4:2001, 4.4]
Note 1 to entry: In the dust collection field this efficiency is called as Partial separation efficiency.
3.1.21
reference material
RM
material, sufficiently homogeneous and stable with respect to one or more specified properties, which
has been established to be fit for its intended use in a measurement process
Note 1 to entry: RM is a generic term.
Note 2 to entry: Properties can be quantitative or qualitative, e.g. identity of substances or species.
Note 3 to entry: Uses may include the calibration of a measurement system, assessment of a measurement
procedure, assigning values to other materials, and quality control.
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ISO 26824:2022(E)
Note 4 to entry: ISO/IEC Guide 99:2007 has an analogous definition but restricts the term “measurement” to
apply to quantitative values. However, ISO/IEC Guide 99:2007, 5.13, Note 3 (VIM), specifically includes qualitative
properties, called “nominal properties”.
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.22
certified reference material
CRM
reference material (3.1.21) characterised by a metrologically valid procedure for one or more specified
properties, accompanied by an RM certificate that provides the value of the specified property, its
associated uncertainty, and a statement of metrological traceability
Note 1 to entry: The concept of value includes a nominal property or a qualitative attribute such as identity or
sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence.
Note 2 to entry: Metrologically valid procedures for the production and certification of RMs are given in, among
others, ISO 17034 and ISO Guide 35.
Note 3 to entry: ISO Guide 31 gives guidance on the contents of RM certificates.
Note 4 to entry: ISO/IEC Guide 99:2007, 5.14 has an analogous definition.
[SOURCE: ISO Guide 35:2017, 3.2]
3.1.23
accuracy
closeness of agreement between a test result or measurement result and the true value (3.1.26)
Note 1 to entry: In practice, the accepted reference value is substituted for the true value (3.1.26).
Note 2 to entry: The term “accuracy”, when applied to a set of test or measurement results, involves a combination
of random components and a common systematic error or bias component.
Note 3 to entry: Accuracy refers to a combination of trueness (3.1.25) and precision (3.1.24).
[SOURCE: ISO 3534-2:2006, 3.3.1]
3.1.24
precision
closeness of agreement between independent test/measurement results obtained under stipulated
conditions
Note 1 to entry: Precision depends only on the distribution of random errors and does not relate to the true value
(3.1.26) or the specified value.
Note 2 to entry: The measure of precision is usually expressed in terms of imprecision and computed as a
standard deviation of the test results or measurement results. Less precision is reflected by a larger standard
deviation.
Note 3 to entry: Quantitative measures of precision depend critically on the stipulated conditions. Repeatability
conditions (3.1.28) and reproducibility conditions are particular sets of extreme stipulated conditions.
[SOURCE: ISO 3534-2:2006, 3.3.4]
3.1.25
trueness
closeness of agreement between the expectation of a test result or a measurement result and a true
value (3.1.26)
Note 1 to entry: The measure of trueness is usually expressed in terms of bias.
Note 2 to entry: Trueness is sometimes referred to as “accuracy of the mean”. This usage is not recommended.
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Note 3 to entry: In practice, the accepted reference value is substituted for the true value.
[SOURCE: ISO 3534-2:2006, 3.3.3]
3.1.26
true value
value which characterizes a quantity or quantitative characteristic perfectly defined in the conditions
which exist when that quantity or quantitative characteristic is considered
Note 1 to entry: The true value of a quantity or quantitative characteristic is a theoretical concept and, in general,
cannot be known exactly.
Note 2 to entry: For an explanation of the term "quantity", refer to ISO 3534-2:2006, Note 1 of 3.2.1.
[SOURCE: ISO 3534-2:2006, 3.2.5]
3.1.27
repeatability
precision under repeatability conditions (3.1.28)
Note 1 to entry: Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the
results.
[SOURCE: ISO 13320:2020, 3.1.20]
3.1.28
repeatability conditions
observation conditions where independent test/measurement results are obtained with the same
method on identical test/measurement items in the same test or measuring facility by the same
operator using the same equipment within short intervals of time
Note 1 to entry: Repeatability conditions include the following:
— the same measurement procedure or test procedure;
— the same operator;
— the same measuring or test equipment used under the same conditions;
— the same location;
— repetition over a short period of time.
[SOURCE: ISO 3534-2:2006, 3.3.6]
3.1.29
method repeatability
closeness of agreement between multiple measurement results of a given property in different aliquots
of a sample, executed by the same operator using the same instrument under identical conditions
within a short period of time
Note 1 to entry: The variability includes the variabilities of sub sampling technique, of the sampled material
together and of the instrument.
[SOURCE: ISO 13320:2020, 3.1.22]
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ISO 26824:2022(E)
3.2 Terms related to representation of particle shape
3.2.1
particle shape
external geometric form of a particle (3.1.1)
Note 1 to entry: Macroshape is a description of the overall form of a particle (3.1.1) defined in terms of the
geometrical proportions of the particle. In general, simple geometrical descriptors calculated from size
measurements made on the particle silhouette are used.
Note 2 to entry: Mesoshape description provides information about details of the particle shape and/or surface
structure that are in a size range not much smaller than the particle proportions.
Note 3 to entry: Microshape
...