ISO 13317-5:2025

International
Standard
ISO 13317-5
First edition
Determination of particle size
2025-01
distribution by gravitational liquid
sedimentation methods —
Part 5:
Photosedimentation techniques
Détermination de la distribution granulométrique par les
méthodes de sédimentation par gravité dans un liquide —
Partie 5: Techniques de photosédimentation
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 6
5 Measurement principle and instrumentation . 8
5.1 General measurement principle .8
5.2 Primary and derived measurement results .10
5.3 Instrumentation .11
6 Measurement data and calculation of distribution function .13
6.1 Primary and derived measurands . 13
6.2 Intrinsically measured distribution functions . 15
6.3 Conversion to volume-weighted distribution functions .17
6.4 Determination of the start position .18
6.5 Assumptions behind data analysis in photosedimentation . 20
6.5.1 Assumptions related to Stokes law . 20
6.5.2 Assumptions related to photometric particle quantification .21
6.6 Working range with respect to particle size and concentration .21
6.6.1 Limits defined by the applicability of Stokes law .21
6.6.2 Limits defined by the applicability of photometric detection . 22
7 Performing size analyses .24
7.1 General .24
7.2 Sampling .24
7.3 Dispersion process and primary sample preparation.24
7.4 Secondary sample preparation (sample conditioning) . 25
7.5 Instrument preparation . 25
7.6 Measurement . 26
7.7 Data analysis . 26
7.8 Reporting .27
8 System qualification and quality control .28
8.1 General remarks . 28
8.2 Reference materials . 29
8.3 Performance qualification. 30
8.4 Measurement uncertainty . 30
Annex A (informative) Measurement position .33
Annex B (informative) Calculation of number-weighted particle size distribution .37
Annex C (informative) Detailed multi-wavelength approach .40
Annex D (informative) Guide to uncertainty determination .42
Annex E (informative) Beyond velocity and size determination. 47
Bibliography .50

iii
Foreword
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Subcommittee SC 4, Particle characterization.
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iv
Introduction
The principles of gravitational photosedimentation and its potential use for the granulometric
characterization of particle systems have been known for several decades. Recent developments in
optoelectronics and data processing have boosted the commercial success and popularity of this
measurement technique, which is currently employed in manifold academic and industrial applications.
This document is a part of the ISO 13317 series that provides a general overview on the principles, techniques,
methods and underlying physics of particle size analysis by gravitational sedimentation. Photosedimentation
employs photometric signals (i.e. transmitted, reflected or scattered light) in order to monitor the changes
in the local particle concentration, which arise by the downward or upward particle migration under
gravity (called hereafter sedimentation). The temporal or spatial functions of these signals can be directly
transformed to distributions of the sedimentation velocity, without referring to model assumptions or being
restricted by essential preconditions. Provided the applicability of Stokes’ law on particle mobility, one can
derive equivalent diameters from the sedimentation velocities (the Stokes diameter) and the corresponding
particle size distributions. Size fractions are then intrinsically weighted by photometric quantities (e.g. light
extinction or scattered light intensity), which is in contrast to the sedimentation techniques described in
ISO 13317-2, ISO 13317-3 and ISO 13317-4. However, conversion into volume-weighted distributions is often
an integrated part of signal processing, which employs established models for light-particle interactions. A
noteworthy feature of gravitational photosedimentation is its ability to finely resolve details in the particle
distribution functions. This is related to the physical fractionating of particle systems under gravity and
constitutes an advantage compared to spectroscopic ensemble techniques.
Gravitational photosedimentation facilitates the granulometric characterization of dispersed materials
of non-zero density contrast to the continuous phase, including solid particles and emulsion droplets.
The available measurement range depends on dispersed and continuous phase properties and typically
amounts to 200 nm to 100 μm for aqueous samples, whereas the sedimentation velocity can be quantified
for the range 0,6 µm/s to 10 mm/s. Also, the working range with regard to particle concentration is strongly
affected by material properties and by particle size, yet it is typically well below 1 vol%. The data analysis
relies on the assumption that all particles have the same density and comparable shape and do not undergo
chemical or physical change in the continuous phase.
In addition, photosedimentation techniques that monitor gravity-induced concentration changes along the
complete sample height, e.g. by position-scanning or time-resolved projection, facilitate the characterization
of dense dispersion beyond particle size, e.g. with respect to clarification, segregation, agglomeration,
consolidation and physico-chemical stability (see ISO/TR 13097). Gravitational photosed
...