ISO 13319:2000
(Main)Determination of particle size distributions — Electrical sensing zone method
Determination of particle size distributions — Electrical sensing zone method
Détermination des répartitions granulométriques — Méthode de la zone de détection électrique
La présente Norme internationale fixe des lignes directrices pour le mesurage granulométrique de particules dispersées dans une solution électrolytique, par la méthode de la zone de détection électrique. Elle n'aborde pas les exigences spécifiques de mesure granulométrique de matériaux spécifiques. La méthode décrite dans la présente Norme internationale mesure les volumes de particules et est applicable aux granulométries d'une étendue comprise entre environ0,6 µm et 1 600 µm.
Določevanje granulacije - Metoda detekcije v električnem polju
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INTERNATIONAL ISO
STANDARD 13319
First edition
2000-04-01
Determination of particle size
distributions — Electrical sensing zone
method
Détermination des répartitions granulométriques — Méthodes de la zone
de détection électrique
Reference number
ISO 13319:2000(E)
©
ISO 2000
---------------------- Page: 1 ----------------------
ISO 13319:2000(E)
PDF disclaimer
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be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this
file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this
area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters
were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event
that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2000
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body
in the country of the requester.
ISO copyright office
Case postale 56 � CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 734 10 79
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2000 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13319:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Terms and definitions .1
3 Symbols .1
4 Principle.2
5 General operation .3
6 Operational procedures .4
7 Calculation of results .10
8 Analysis .11
9 Validation.11
Annex A (informative) Table of materials and electrolyte solutions.12
Annex B (informative) Technique using two (or more) sensors .23
Annex C (informative) Example of calibration by mass integration .25
Annex D (informative) Calibration and control of frequently used orifices .27
Annex E (informative) Data sheet .28
Bibliography.30
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ISO 13319:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 13319 was prepared by Technical Committee ISO/TC 24, Sieves, sieving, and other
sizing methods, Subcommittee SC 4, Sizing by methods other than sieving.
Annexes A to E of this International Standard are for information only.
iv © ISO 2000 – All rights reserved
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INTERNATIONAL STANDARD ISO 13319:2000(E)
Determination of particle size distributions — Electrical sensing
zone method
1 Scope
This International Standard gives guidance on the measurement of the size distributions of particles dispersed in an
electrolyte solution using the electrical sensing zone method. It does not address the specific requirements of the
particle size measurement of specific materials. The method described in this International Standard measures
particle volumes and reports in the range about from 0,6 �m to1600 �m.
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
2.1
dead time
time during which the electronics are not able to detect particles due to the signal processing of a previous particle
2.2
orifice
small-diameter hole through which suspension is drawn
2.3
sensing zone
volume of electrolyte solution within, and around, the orifice in which a particle is detected
2.4
sampling volume
volume of suspension that is analysed
3 Symbols
D orifice diameter, in �m
K calibration constant of diameter
d
K calibration constant of mean diameter
d
� standard deviation of mean calibration constant
K
d
m mass of sample in beaker, in g
V volume of electrolyte solution in which m is dispersed, in ml
T
V analysis volume, in ml
m
�N number of counts in a size interval i
i
�1
� mass of the particles per volume of the electrolyte it displaces, in g�ml
V arithmetic mean volume for a particular size interval i,inml
i
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ISO 13319:2000(E)
V volume of the particle obtained from the threshold, or channel boundary and instrument units; without
i
an arbitrary calibration to particle diameter (i.e. V = tIA,where t = threshold level, I = current through
i
aperture and A = attenuation factor), in ml
x diameter of a sphere with volume equivalent to that of the particle, in�m
x , x , x the values of x corresponding to the 50 %, 10 % and 90 % percentile points of the cumulative per cent
50 10 90
undersize distributions, in �m
4Principle
The response, i.e. the electrical pulse generated when a particle passes through the orifice, has been found both
experimentally and theoretically to be proportional to the particle volume (see Bibliography). A dilute suspension of
particles dispersed in an electrolyte solution is stirred to provide a homogeneous mixture and is drawn through a
small orifice, or aperture, in an insulating wall. A current applied across two electrodes, placed on each side of the
orifice, enables the particles to be sensed by the electrical impedance changes as they pass through the orifice.
The particle-generated pulses are amplified and counted and the pulse height is analysed. After employing a
calibration factor, a distribution of the number of particles against the volume-equivalent diameter is obtained. This
distribution is usually converted to percentage by mass versus particle size, where the size parameter is expressed
as the diameter of a sphere of volume and density equal to that of the particle. See Figure 1.
Key
1 Volumetric metering device 6 Output
2 Valve 7 Pulse-height analyser
3 Pulse amplifier 8 Stirred suspension of particles in electrolyte solution
4 Oscilloscope pulse display 9 Aperture
5 Counting circuit 10 Counter start/stop
Figure 1 — Diagram illustrating the principle of the electrical sensing zone method
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ISO 13319:2000(E)
5 General operation
5.1 Response
If the particles are spherical, the electrical response is proportional to the volume of the particles. This has also
been shown to be true for particles of other shapes; however, the constant of proportionality (i.e. the instrument’s
calibration constant) may be different. In general, particles should have a low conductivity with respect to the
electrolyte solution, but conducting particles can be measured.
5.2 Size limits
The lower size limit of the electrical sensing zone method is generally considered to be restricted only by thermal
and electronic noise. It is normally stated to be about 0,6�m, but under favourable conditions a lower limit is
possible. There is no theoretical upper limit, and for particles having a density similar to that of the electrolyte
solution, the largest orifice available (normally 2 000�m) may be used.
When the particle density is high, the upper size limit is reached when the particles can no longer be kept in
homogeneous suspension. In this case, the viscosity and/or the density of the electrolyte solution has to be
increased, for example by the addition of glycerol or sucrose.
The size range for a single orifice sensor is proportional to the orifice diameter, D. The response has been found to
depend linearly on D over a range from 0,015 D to 0,80 D (i.e. 1,5�mto 80�m for a 100�m orifice), although the
orifice may become prone to blockage at levels greater than 0,60 D. This range can be extended by using two or
more sensors (see annex B) but in practice this procedure can be avoided by the careful selection of the diameter
of one sensor, to achieve an acceptable range.
The response of the instrument is dependent on the effective electrical resistance of the particle, which is usually
high. The measurement of conducting particles (e.g. metals, carbon, silicon and many types of cells and
organisms, such as blood cells) requires more time to implement. The particles can become electrically translucent
(i.e. give a smaller electrical pulse than their volume indicates) if a voltage, typically of 10 V to 15 V or more, is
applied between the electrodes. To obtain acceptable results, a distribution is obtained under normal conditions.
The analysis is then repeated using half the current and twice the gain (1/attenuation). The distributions should be
the same. If they are not, the procedure should be repeated using an even lower current.
5.3 Effect of coincident particle passage
Ideal data would result if particles traversed the orifice singly, when each particle would produce a single pulse.
When two or more particles arrive in the sensing zone together, the resulting pulse will be complex. Either a single
large pulse will be obtained, resulting in a loss of count and effectively registering a single larger particle, or the
count will be correct but the reported size of each will be increased, or some particles will not be counted. These
effects will distort the particle distribution obtained but can be minimized by using low concentrations. Table 1
shows counts per millilitre for the coincidence to be 5 % (i.e. approximately only one particle in twenty is affected).
Counts per millilitre should always be less than these quoted values. Since particle size distributions should not be
a function of concentration, the effect of coincidence can be tested by obtaining a distribution at one concentration
and comparing it with that obtained when the concentration is halved. In such a test, repeat such dilutions until the
reduction in count in a channel with the largest number decreases in proportion to the dilution. This should always
be done when analysing very narrow size distributions, as this is where the effect of coincidence is most noticeable.
5.4 Dead time
In some modern instruments, pulse-height analysis routines are used to process the data. Since it takes a finite
time to process each pulse, it is possible that the analyser may not count particles for a given time after receiving a
pulse. This means that, for a relatively high count rate, a significant proportion of the counts may be lost. Since
dead time is not a function of the pulse height, the loss will be proportional to the counts in each channel and will
not affect the size distribution. However, if concentration is to be reported or the mass integration method of
calibration (see 6.11.3) is to be used, the effect can be kept to a minimum by using dilute suspensions (e.g. at
< 5 % coincidence) and setting up the instrument so that the pulses in the lowest channels are not counted. This is
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ISO 13319:2000(E)
done by first obtaining a count distribution and observing the number of counts per channel. A typical result is
shown in Figure 2. By restricting the counts in the lowest channel to that shown by A, the dead time will be
minimized.
In normal operation, this dead time will not cause any distortion of the size distribution since all particles will have
the same chance of not being counted, provided that a large number of particles, at least 100 000, are counted.
However dead time will affect the accuracy of the mass integration method of calibration (see 6.11.3), when there
will be an apparent loss of mass.
Counts at channels below A are noise counts. True particle counts are at the higher channels
Figure 2 — Typical results
5.5 Repeatability of counts
It has been shown that, in a correctly performed analysis, the number of counts in each channel is a random
variable which follows Poisson's law. This means that the standard deviation of a number of counts N approximates
to N . Thus, in a series of replicate runs the number of counts in a channel, N , N , N , etc., which yield a
i,1 i,2 i,3
mean count N with 95 % confidence, the replicate counts N should be in the rangeNN� 19, 6 ; i.e. if the count
i i,n ii
N is 100 000, the uncertainty is � 619. If 20 replicate analyses yield more than one outside this range, the sample
i
preparation procedure should be re-examined (see 6.7). This statistical test can be performed on single channels,
groups of channels, or on the total particle count.
6 Operational procedures
6.1 Instrument location
The instrument should be sited in a clean environment that is free from electrical interference and vibration. If
organic solvents are to be used, the area should be well ventilated.
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ISO 13319:2000(E)
6.2 Linearity of the sensor/amplifier system
The linearity of the sensor/amplifier system can be checked using three monodisperse particles of certified
diameter. In a suitable electrolyte solution, the instrument is calibrated with particles at about 0,3D (see 6.11.2).
Two further sizes of microspheres are then added to the suspension (one of size � 0,2D and one � 0,5D). The
suspension is re-analysed and the size corresponding to these extra peaks has to correspond to the quoted size of
the particles to within 5 %.
6.3 Linearity of counting system
The linearity of the counting system can be tested by obtaining three counts at an arbitrary concentration. The
concentration is then reduced and three further counts obtained. The ratio of the mean of the counts should be the
same as the dilution. If the agreement is not within 5 %, the test should be repeated comparing the two lowest
dilutions; (coincidence may prevent the true count being obtained if the concentration is too high). Subsequent
analyses should be carried out at the dilution giving the best results.
6.4 Volume V of analysed suspension
m
If particle concentrations are to be determined or the mass integration method of calibration (see 6.11.3) is to be
used, it is necessary to check the volume V of the analysed suspension, which is usually only guaranteed at one
m
metered value by the manufacturer. This value of the analysed volume should be known. Using a suspension of
particles, at a statistically valid count level (see 6.3), measure the total particle count with that volume three times.
Switch to another analysis volume and obtain the total particle counts at least three times. The ratio of the total
number of counts will be the ratio of the guaranteed volume to the selected volume. All counts should be recorded.
6.5 Choice of electrolyte solution
An electrolyte solution should be selected in which the sample is stable. The electrolyte solution should not
dissolve, flocculate, react or otherwise interfere with the state of dispersion of the sample in the measurement time,
typically up to 5 min.
Particles insoluble in water can be analysed in aqueous electrolytes, such as 50 g/l hydrated trisodium
orthophosphate solution, or 10 g/l sodium chloride solution. Particles soluble in water can often be analysed in
50 g/l lithium chloride solution in methanol, or 50 g/l ammonium thiocyanate solution in iso-propanol. See annex A
for other recommended electrolyte solutions for many common materials.
6.6 Preparation of electrolyte solution
The electrolyte solution should be well filtered with a membrane filter for which the pore size is less than the
diameter of the smallest particle measured, as it is essential that its background count should be as low as is
practicable. All glassware and other apparatus used should be pre-rinsed with filtered electrolyte solution.
Background counts should not exceed the values given in Table 1 or yield a total equivalent volume in excess of
0,1 % of the total volume of particles subsequently measured in the same sampling volume.
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ISO 13319:2000(E)
Table 1 — Counts for background and 5 % coincidence for typical orifice diameters
Orifice Analysis Background Count for 5 %
a b c
diameter
volume counts coincidence
D
V N
m
�m ml
1 000 2 2 80
560 2 10 455
400 2 25 1 250
280 2 75 3 645
200 2 200 10 000
140 2 600 29 150
100 0,5 400 20 000
70 0,5 1 200 58 500
50 0,05 300 16 000
30 0,05 1 500 74 000
20 0,05 5 000 250 000
a
For other sampling volumes, use pro rata values.
b
Suggested maximum counts.
10
41� 0 V
c
m
Calculated using the equation
N �
3
D
6.7 Recommended sample preparation and dispersion
6.7.1 General
A dispersant should be selected from the recommendations in ISO 14887 or annex A.
6.7.2 Method 1: Using a paste
3
The sample should be subdivided to about 0,2 cm . If the sample is in the form of a powder, it should be worked
and kneaded gently with a flexible spatula with a few drops of suitable dispersant to break down agglomerates. A
mass of about 20 mg to 50 mg of the paste is transferred into a round-bottomed beaker and thinned with
dispersant, followed by a few drops of electrolyte solution. The beaker is nearly filled with electrolyte solution and
placed in a low-power ultrasonic bath for 1 min, stirring occasionally. A suitable design of beaker of 400 ml capacity
with a baffle is shown in Figure 3. The ultrasonic bath should be in the range 50 W to 100 W, 60 kHz to 80 kHz, and
a stop watch is recommended for a reproducible dispersion technique.
NOTE The use of high-energy ultrasonic baths and probes, blenders and mixers can cause both agglomeration and
fracture of particles.
If the sample is not required to be fully dispersed, it may be added to the electrolyte solution and dispersant while
stirring.
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ISO 13319:2000(E)
Figure 3 — Example of a beaker with baffle and stirrer
6.7.3 Method 2: Alternative method applicable to low-density particles of less than 50����m
The sample should be subdivided to about 1 g of the sample. This is mixed with the dispersant and is added to the
electrolyte and solution. The beaker (see Figure 3) containing the suspension is then placed in an ultrasonic bath
for about 45 s. After stirring this stock suspension well, 5 ml is withdrawn using a pipette and is added to
approximately 400 ml of electrolyte solution and placed in the ultrasonic bath for a further 15 s. When using this
method, it is important that at least two samples are withdrawn from the stock suspension and analysed to ensure
repeatability of the aliquot sampling and the analysis.
6.7.4 Suspensions and emulsions
Suspensions and emulsions may be diluted by slowly adding electrolyte solution. To avoid “dilution shock”, oil-in
water emulsions may be initially diluted with distilled or de-ionized water.
6.7.5 Verification of the dispersion
A small sample of the dispersion may be placed on a microscope slide and used to verify the degree of dispersion
and to estimate the size range of the particles.
6.8 Choice of orifice(s) and sampling volume(s)
From the microscope examination (6.7.4), estimate the diameter of the largest particles present.
Choose an orifice for the size analysis such that the diameter of the largest particles to be analysed is less than
approximately 50 % of the diameter of the orifice, selected to reduce the possibility of blocking the orifice . If there
is a considerable proportion of sample below the lower size limit of that orifice (1,5 % of its diameter), a second and
possibly a third smaller orifice will be needed (see annex B).
Select a suitable sampling volume with reference to Table 1. It may be necessary to analyse a number of these
sampling volumes to accumulate a statistically valid total number of particles, for example about 100 000 [i.e. a
precision of � 619 (see 5.5) or better than� 1 %]. Counting fewer particles will reduce the precision, but this may be
necessary when using the larger orifices or performing contamination studies.
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ISO 13319:2000(E)
6.9 Clearing an orifice blockage
Orifices below 100�m in diameter may become blocked with extraneous particles, particularly if care is not
exercised in the clean handling, careful filtration, and thorough rinsing of beakers and associated equipment. A
blockage is readily seen by means of the viewing optics provided with the analyser.
A partial blockage may be indicated by different flow times for the same metered volume. Blockages can be
removed automatically or by one of the following techniques:
a) Back flushing: Reversing the flow through the orifice may be sufficient to clear a blockage.
b) Boiling: It is possible to use the heating effect of the current to boil the blockage out. This is done by using a
high orifice current.
c) Brushing: It is often possible to brush the particles off the orifice by using a small high-quality soft-hair brush
with the hairs cut short. Care should be taken not to damage the orifice.
d) Air pressure.
e) Ultrasonic cleaning: With the orifice tube filled with electrolyte solution, the end is dipped into a low-power
ultrasonic bath for about 1 s. Repeat this operation as necessary. This method is very effective but extreme
care should be taken as it is possible to damage the orifice.
Caution — This method should not be used for orifices of 50����m or less.
6.10 Stability of dispersion
With the most suitable orifice fitted, and the suspension prepared, dry the outside of the beaker and place it on the
sample stand of the instrument. Adjust the stirrer for maximum effect without creating a vortex which will entrain
bubbles.
The stability of the dispersion during the analysis time is then checked. A full size analysis is made as soon as
possible after dispersion; the suspension is then stirred for 5 min to 10 min and finally is reanalysed. Cumulative
counts are recorded at size levels close to 30 % and 5 % of the orifice diameter (denoted x and x
max min
respectively). Changes in the counts greater than those expected from statistics, i.e. N , will indicate that the
dispersion is not stable. Table 2 details some possible causes.
Table 2 — Examples of suspected phenomena in dispersion
Change in count at
Suggests
x x
max min
no change no change Stable dispersion
increase increase Crystallization, precipitation
decrease decrease Dissolution
decrease increase Size reduction, deflocculation
increase decrease Flocculation, agglomeration
decrease no change Settling of large particles
In all but the first case given in Table 2, a different dispersant/electrolyte solution combination should be tried, and
the dispersion rechecked.
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ISO 13319:2000(E)
6.11 Calibration
6.11.1 General
Electrical sensing zone instruments are usually calibrated using polymer latex microspheres of known size and
narrow size distribution. However, the mass integration method (6.11.3) is generally believed to be closer to an
absolute method. Here the volume concentration of the suspension as determined by the instrument is compared
to the true volume concentration determined from the mass per unit volume and the immersed density of the
particles. This calibration method is directly traceable and there is no assumption made about the shape, porosity
or electrical conductivity of the particles. Unfortunately, some instruments have a dead time in the pulse-processing
circuitry which can be significant and can correspond to an effective loss in the mass of the particles analysed. This
loss will depend on the total number of particles counted, but does not affect the size distribution obtained since the
same proportion of the count will be lost for all size classes.
Calibration should be checked on a regular basis to ensure that the change in the calibration constant is less than
1,0 %, or every time an orifice tube or an electrolyte solution is changed. See annex D for a method for calibration
of frequently used orifices.
6.11.2 Calibration procedure: microsphere calibration
Microspheres of narrow size distribution with a single mode, characterized by a variety of other methods, are
available. They should be traceable to the micrometre, to a Community Bureau of Reference (BCR), a National
Institute of Standards and Technology (NIST) or similar reference material. The calibration method used depends
on the assayed size parameter of the microspheres and the analyser used (contact the instrument manufacturers
for details). One method is to obtain a histogram (frequency) plot of the number of particles against channels of
equal width (on a linear scale). The size at the centre of the channel with the greatest number of particles
corresponds closely to the modal size of the calibration material if the distribution is symmetrical. If the distribution
is not symmetrical, the fractional channel position is calculated from the counts in the channels on either side of the
central channel. The calibration factor is the ratio of the modal size of the calibration material to the size as reported
on the instrument.
6.11.3 Calibration procedure: mass integration method (self-calibration)
6.11.3.1 A narrow size-range fraction of the material under test is prepared by sieving or a similar separation
method. At least 99 % of the mass of the particles should lie within a size range of no more than 10:1, so that all
can be measured using one orifice.
6.11.3.2 Using a balance weighing to an accuracy of 0,1 mg, a relative-density bottle, pipettes and the usual
particle-dispersion method, the immersed density � of the material in the electrolyte solution to be used for the
s
analysis is determined.
6.11.3.3 A suspension is prepared by dispersing a mass m of the powder in a volume V of the electrolyte and
g T
dispersing agent.
6.11.3.4 The calibration factor K for the instrument is then determined by measuring very carefully the size
d
distribution using an accurately known sampling volume, V , ensuring that the orifice is absolutely clear. A number
m
of sampling volumes may be counted so that the total number of particles is in excess of 100 000. The particle
concentration used should be much less than the 5 % coincidence limit.
K is calculated from the formula
d
F I
�NV
� ii m �
�
3 s
K � � (1)
G J
d
G J
6 V V
m T
H K
6.11.3.5 For the results to be accurate it is not sufficient to accept the nominal value of the analysis volume V .
m
This should be measured relative to the certified analysis volume as described in 6.4 or the apparatus returned to
the manufacturer for accurate measurement. For an e
...
SLOVENSKI STANDARD
SIST ISO 13319:2002
01-junij-2002
'RORþHYDQMHJUDQXODFLMH0HWRGDGHWHNFLMHYHOHNWULþQHPSROMX
Determination of particle size distributions -- Electrical sensing zone method
Détermination des répartitions granulométriques -- Méthode de la zone de détection
électrique
Ta slovenski standard je istoveten z: ISO 13319:2000
ICS:
19.120 Analiza velikosti delcev. Particle size analysis. Sieving
Sejanje
SIST ISO 13319:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 13319:2002
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SIST ISO 13319:2002
INTERNATIONAL ISO
STANDARD 13319
First edition
2000-04-01
Determination of particle size
distributions — Electrical sensing zone
method
Détermination des répartitions granulométriques — Méthodes de la zone
de détection électrique
Reference number
ISO 13319:2000(E)
©
ISO 2000
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SIST ISO 13319:2002
ISO 13319:2000(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not
be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this
file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this
area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters
were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event
that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2000
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body
in the country of the requester.
ISO copyright office
Case postale 56 � CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 734 10 79
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2000 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 13319:2002
ISO 13319:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Terms and definitions .1
3 Symbols .1
4 Principle.2
5 General operation .3
6 Operational procedures .4
7 Calculation of results .10
8 Analysis .11
9 Validation.11
Annex A (informative) Table of materials and electrolyte solutions.12
Annex B (informative) Technique using two (or more) sensors .23
Annex C (informative) Example of calibration by mass integration .25
Annex D (informative) Calibration and control of frequently used orifices .27
Annex E (informative) Data sheet .28
Bibliography.30
© ISO 2000 – All rights reserved iii
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SIST ISO 13319:2002
ISO 13319:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 13319 was prepared by Technical Committee ISO/TC 24, Sieves, sieving, and other
sizing methods, Subcommittee SC 4, Sizing by methods other than sieving.
Annexes A to E of this International Standard are for information only.
iv © ISO 2000 – All rights reserved
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SIST ISO 13319:2002
INTERNATIONAL STANDARD ISO 13319:2000(E)
Determination of particle size distributions — Electrical sensing
zone method
1 Scope
This International Standard gives guidance on the measurement of the size distributions of particles dispersed in an
electrolyte solution using the electrical sensing zone method. It does not address the specific requirements of the
particle size measurement of specific materials. The method described in this International Standard measures
particle volumes and reports in the range about from 0,6 �m to1600 �m.
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
2.1
dead time
time during which the electronics are not able to detect particles due to the signal processing of a previous particle
2.2
orifice
small-diameter hole through which suspension is drawn
2.3
sensing zone
volume of electrolyte solution within, and around, the orifice in which a particle is detected
2.4
sampling volume
volume of suspension that is analysed
3 Symbols
D orifice diameter, in �m
K calibration constant of diameter
d
K calibration constant of mean diameter
d
� standard deviation of mean calibration constant
K
d
m mass of sample in beaker, in g
V volume of electrolyte solution in which m is dispersed, in ml
T
V analysis volume, in ml
m
�N number of counts in a size interval i
i
�1
� mass of the particles per volume of the electrolyte it displaces, in g�ml
V arithmetic mean volume for a particular size interval i,inml
i
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SIST ISO 13319:2002
ISO 13319:2000(E)
V volume of the particle obtained from the threshold, or channel boundary and instrument units; without
i
an arbitrary calibration to particle diameter (i.e. V = tIA,where t = threshold level, I = current through
i
aperture and A = attenuation factor), in ml
x diameter of a sphere with volume equivalent to that of the particle, in�m
x , x , x the values of x corresponding to the 50 %, 10 % and 90 % percentile points of the cumulative per cent
50 10 90
undersize distributions, in �m
4Principle
The response, i.e. the electrical pulse generated when a particle passes through the orifice, has been found both
experimentally and theoretically to be proportional to the particle volume (see Bibliography). A dilute suspension of
particles dispersed in an electrolyte solution is stirred to provide a homogeneous mixture and is drawn through a
small orifice, or aperture, in an insulating wall. A current applied across two electrodes, placed on each side of the
orifice, enables the particles to be sensed by the electrical impedance changes as they pass through the orifice.
The particle-generated pulses are amplified and counted and the pulse height is analysed. After employing a
calibration factor, a distribution of the number of particles against the volume-equivalent diameter is obtained. This
distribution is usually converted to percentage by mass versus particle size, where the size parameter is expressed
as the diameter of a sphere of volume and density equal to that of the particle. See Figure 1.
Key
1 Volumetric metering device 6 Output
2 Valve 7 Pulse-height analyser
3 Pulse amplifier 8 Stirred suspension of particles in electrolyte solution
4 Oscilloscope pulse display 9 Aperture
5 Counting circuit 10 Counter start/stop
Figure 1 — Diagram illustrating the principle of the electrical sensing zone method
2 © ISO 2000 – All rights reserved
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SIST ISO 13319:2002
ISO 13319:2000(E)
5 General operation
5.1 Response
If the particles are spherical, the electrical response is proportional to the volume of the particles. This has also
been shown to be true for particles of other shapes; however, the constant of proportionality (i.e. the instrument’s
calibration constant) may be different. In general, particles should have a low conductivity with respect to the
electrolyte solution, but conducting particles can be measured.
5.2 Size limits
The lower size limit of the electrical sensing zone method is generally considered to be restricted only by thermal
and electronic noise. It is normally stated to be about 0,6�m, but under favourable conditions a lower limit is
possible. There is no theoretical upper limit, and for particles having a density similar to that of the electrolyte
solution, the largest orifice available (normally 2 000�m) may be used.
When the particle density is high, the upper size limit is reached when the particles can no longer be kept in
homogeneous suspension. In this case, the viscosity and/or the density of the electrolyte solution has to be
increased, for example by the addition of glycerol or sucrose.
The size range for a single orifice sensor is proportional to the orifice diameter, D. The response has been found to
depend linearly on D over a range from 0,015 D to 0,80 D (i.e. 1,5�mto 80�m for a 100�m orifice), although the
orifice may become prone to blockage at levels greater than 0,60 D. This range can be extended by using two or
more sensors (see annex B) but in practice this procedure can be avoided by the careful selection of the diameter
of one sensor, to achieve an acceptable range.
The response of the instrument is dependent on the effective electrical resistance of the particle, which is usually
high. The measurement of conducting particles (e.g. metals, carbon, silicon and many types of cells and
organisms, such as blood cells) requires more time to implement. The particles can become electrically translucent
(i.e. give a smaller electrical pulse than their volume indicates) if a voltage, typically of 10 V to 15 V or more, is
applied between the electrodes. To obtain acceptable results, a distribution is obtained under normal conditions.
The analysis is then repeated using half the current and twice the gain (1/attenuation). The distributions should be
the same. If they are not, the procedure should be repeated using an even lower current.
5.3 Effect of coincident particle passage
Ideal data would result if particles traversed the orifice singly, when each particle would produce a single pulse.
When two or more particles arrive in the sensing zone together, the resulting pulse will be complex. Either a single
large pulse will be obtained, resulting in a loss of count and effectively registering a single larger particle, or the
count will be correct but the reported size of each will be increased, or some particles will not be counted. These
effects will distort the particle distribution obtained but can be minimized by using low concentrations. Table 1
shows counts per millilitre for the coincidence to be 5 % (i.e. approximately only one particle in twenty is affected).
Counts per millilitre should always be less than these quoted values. Since particle size distributions should not be
a function of concentration, the effect of coincidence can be tested by obtaining a distribution at one concentration
and comparing it with that obtained when the concentration is halved. In such a test, repeat such dilutions until the
reduction in count in a channel with the largest number decreases in proportion to the dilution. This should always
be done when analysing very narrow size distributions, as this is where the effect of coincidence is most noticeable.
5.4 Dead time
In some modern instruments, pulse-height analysis routines are used to process the data. Since it takes a finite
time to process each pulse, it is possible that the analyser may not count particles for a given time after receiving a
pulse. This means that, for a relatively high count rate, a significant proportion of the counts may be lost. Since
dead time is not a function of the pulse height, the loss will be proportional to the counts in each channel and will
not affect the size distribution. However, if concentration is to be reported or the mass integration method of
calibration (see 6.11.3) is to be used, the effect can be kept to a minimum by using dilute suspensions (e.g. at
< 5 % coincidence) and setting up the instrument so that the pulses in the lowest channels are not counted. This is
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ISO 13319:2000(E)
done by first obtaining a count distribution and observing the number of counts per channel. A typical result is
shown in Figure 2. By restricting the counts in the lowest channel to that shown by A, the dead time will be
minimized.
In normal operation, this dead time will not cause any distortion of the size distribution since all particles will have
the same chance of not being counted, provided that a large number of particles, at least 100 000, are counted.
However dead time will affect the accuracy of the mass integration method of calibration (see 6.11.3), when there
will be an apparent loss of mass.
Counts at channels below A are noise counts. True particle counts are at the higher channels
Figure 2 — Typical results
5.5 Repeatability of counts
It has been shown that, in a correctly performed analysis, the number of counts in each channel is a random
variable which follows Poisson's law. This means that the standard deviation of a number of counts N approximates
to N . Thus, in a series of replicate runs the number of counts in a channel, N , N , N , etc., which yield a
i,1 i,2 i,3
mean count N with 95 % confidence, the replicate counts N should be in the rangeNN� 19, 6 ; i.e. if the count
i i,n ii
N is 100 000, the uncertainty is � 619. If 20 replicate analyses yield more than one outside this range, the sample
i
preparation procedure should be re-examined (see 6.7). This statistical test can be performed on single channels,
groups of channels, or on the total particle count.
6 Operational procedures
6.1 Instrument location
The instrument should be sited in a clean environment that is free from electrical interference and vibration. If
organic solvents are to be used, the area should be well ventilated.
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ISO 13319:2000(E)
6.2 Linearity of the sensor/amplifier system
The linearity of the sensor/amplifier system can be checked using three monodisperse particles of certified
diameter. In a suitable electrolyte solution, the instrument is calibrated with particles at about 0,3D (see 6.11.2).
Two further sizes of microspheres are then added to the suspension (one of size � 0,2D and one � 0,5D). The
suspension is re-analysed and the size corresponding to these extra peaks has to correspond to the quoted size of
the particles to within 5 %.
6.3 Linearity of counting system
The linearity of the counting system can be tested by obtaining three counts at an arbitrary concentration. The
concentration is then reduced and three further counts obtained. The ratio of the mean of the counts should be the
same as the dilution. If the agreement is not within 5 %, the test should be repeated comparing the two lowest
dilutions; (coincidence may prevent the true count being obtained if the concentration is too high). Subsequent
analyses should be carried out at the dilution giving the best results.
6.4 Volume V of analysed suspension
m
If particle concentrations are to be determined or the mass integration method of calibration (see 6.11.3) is to be
used, it is necessary to check the volume V of the analysed suspension, which is usually only guaranteed at one
m
metered value by the manufacturer. This value of the analysed volume should be known. Using a suspension of
particles, at a statistically valid count level (see 6.3), measure the total particle count with that volume three times.
Switch to another analysis volume and obtain the total particle counts at least three times. The ratio of the total
number of counts will be the ratio of the guaranteed volume to the selected volume. All counts should be recorded.
6.5 Choice of electrolyte solution
An electrolyte solution should be selected in which the sample is stable. The electrolyte solution should not
dissolve, flocculate, react or otherwise interfere with the state of dispersion of the sample in the measurement time,
typically up to 5 min.
Particles insoluble in water can be analysed in aqueous electrolytes, such as 50 g/l hydrated trisodium
orthophosphate solution, or 10 g/l sodium chloride solution. Particles soluble in water can often be analysed in
50 g/l lithium chloride solution in methanol, or 50 g/l ammonium thiocyanate solution in iso-propanol. See annex A
for other recommended electrolyte solutions for many common materials.
6.6 Preparation of electrolyte solution
The electrolyte solution should be well filtered with a membrane filter for which the pore size is less than the
diameter of the smallest particle measured, as it is essential that its background count should be as low as is
practicable. All glassware and other apparatus used should be pre-rinsed with filtered electrolyte solution.
Background counts should not exceed the values given in Table 1 or yield a total equivalent volume in excess of
0,1 % of the total volume of particles subsequently measured in the same sampling volume.
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ISO 13319:2000(E)
Table 1 — Counts for background and 5 % coincidence for typical orifice diameters
Orifice Analysis Background Count for 5 %
a b c
diameter
volume counts coincidence
D
V N
m
�m ml
1 000 2 2 80
560 2 10 455
400 2 25 1 250
280 2 75 3 645
200 2 200 10 000
140 2 600 29 150
100 0,5 400 20 000
70 0,5 1 200 58 500
50 0,05 300 16 000
30 0,05 1 500 74 000
20 0,05 5 000 250 000
a
For other sampling volumes, use pro rata values.
b
Suggested maximum counts.
10
41� 0 V
c
m
Calculated using the equation
N �
3
D
6.7 Recommended sample preparation and dispersion
6.7.1 General
A dispersant should be selected from the recommendations in ISO 14887 or annex A.
6.7.2 Method 1: Using a paste
3
The sample should be subdivided to about 0,2 cm . If the sample is in the form of a powder, it should be worked
and kneaded gently with a flexible spatula with a few drops of suitable dispersant to break down agglomerates. A
mass of about 20 mg to 50 mg of the paste is transferred into a round-bottomed beaker and thinned with
dispersant, followed by a few drops of electrolyte solution. The beaker is nearly filled with electrolyte solution and
placed in a low-power ultrasonic bath for 1 min, stirring occasionally. A suitable design of beaker of 400 ml capacity
with a baffle is shown in Figure 3. The ultrasonic bath should be in the range 50 W to 100 W, 60 kHz to 80 kHz, and
a stop watch is recommended for a reproducible dispersion technique.
NOTE The use of high-energy ultrasonic baths and probes, blenders and mixers can cause both agglomeration and
fracture of particles.
If the sample is not required to be fully dispersed, it may be added to the electrolyte solution and dispersant while
stirring.
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ISO 13319:2000(E)
Figure 3 — Example of a beaker with baffle and stirrer
6.7.3 Method 2: Alternative method applicable to low-density particles of less than 50����m
The sample should be subdivided to about 1 g of the sample. This is mixed with the dispersant and is added to the
electrolyte and solution. The beaker (see Figure 3) containing the suspension is then placed in an ultrasonic bath
for about 45 s. After stirring this stock suspension well, 5 ml is withdrawn using a pipette and is added to
approximately 400 ml of electrolyte solution and placed in the ultrasonic bath for a further 15 s. When using this
method, it is important that at least two samples are withdrawn from the stock suspension and analysed to ensure
repeatability of the aliquot sampling and the analysis.
6.7.4 Suspensions and emulsions
Suspensions and emulsions may be diluted by slowly adding electrolyte solution. To avoid “dilution shock”, oil-in
water emulsions may be initially diluted with distilled or de-ionized water.
6.7.5 Verification of the dispersion
A small sample of the dispersion may be placed on a microscope slide and used to verify the degree of dispersion
and to estimate the size range of the particles.
6.8 Choice of orifice(s) and sampling volume(s)
From the microscope examination (6.7.4), estimate the diameter of the largest particles present.
Choose an orifice for the size analysis such that the diameter of the largest particles to be analysed is less than
approximately 50 % of the diameter of the orifice, selected to reduce the possibility of blocking the orifice . If there
is a considerable proportion of sample below the lower size limit of that orifice (1,5 % of its diameter), a second and
possibly a third smaller orifice will be needed (see annex B).
Select a suitable sampling volume with reference to Table 1. It may be necessary to analyse a number of these
sampling volumes to accumulate a statistically valid total number of particles, for example about 100 000 [i.e. a
precision of � 619 (see 5.5) or better than� 1 %]. Counting fewer particles will reduce the precision, but this may be
necessary when using the larger orifices or performing contamination studies.
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ISO 13319:2000(E)
6.9 Clearing an orifice blockage
Orifices below 100�m in diameter may become blocked with extraneous particles, particularly if care is not
exercised in the clean handling, careful filtration, and thorough rinsing of beakers and associated equipment. A
blockage is readily seen by means of the viewing optics provided with the analyser.
A partial blockage may be indicated by different flow times for the same metered volume. Blockages can be
removed automatically or by one of the following techniques:
a) Back flushing: Reversing the flow through the orifice may be sufficient to clear a blockage.
b) Boiling: It is possible to use the heating effect of the current to boil the blockage out. This is done by using a
high orifice current.
c) Brushing: It is often possible to brush the particles off the orifice by using a small high-quality soft-hair brush
with the hairs cut short. Care should be taken not to damage the orifice.
d) Air pressure.
e) Ultrasonic cleaning: With the orifice tube filled with electrolyte solution, the end is dipped into a low-power
ultrasonic bath for about 1 s. Repeat this operation as necessary. This method is very effective but extreme
care should be taken as it is possible to damage the orifice.
Caution — This method should not be used for orifices of 50����m or less.
6.10 Stability of dispersion
With the most suitable orifice fitted, and the suspension prepared, dry the outside of the beaker and place it on the
sample stand of the instrument. Adjust the stirrer for maximum effect without creating a vortex which will entrain
bubbles.
The stability of the dispersion during the analysis time is then checked. A full size analysis is made as soon as
possible after dispersion; the suspension is then stirred for 5 min to 10 min and finally is reanalysed. Cumulative
counts are recorded at size levels close to 30 % and 5 % of the orifice diameter (denoted x and x
max min
respectively). Changes in the counts greater than those expected from statistics, i.e. N , will indicate that the
dispersion is not stable. Table 2 details some possible causes.
Table 2 — Examples of suspected phenomena in dispersion
Change in count at
Suggests
x x
max min
no change no change Stable dispersion
increase increase Crystallization, precipitation
decrease decrease Dissolution
decrease increase Size reduction, deflocculation
increase decrease Flocculation, agglomeration
decrease no change Settling of large particles
In all but the first case given in Table 2, a different dispersant/electrolyte solution combination should be tried, and
the dispersion rechecked.
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ISO 13319:2000(E)
6.11 Calibration
6.11.1 General
Electrical sensing zone instruments are usually calibrated using polymer latex microspheres of known size and
narrow size distribution. However, the mass integration method (6.11.3) is generally believed to be closer to an
absolute method. Here the volume concentration of the suspension as determined by the instrument is compared
to the true volume concentration determined from the mass per unit volume and the immersed density of the
particles. This calibration method is directly traceable and there is no assumption made about the shape, porosity
or electrical conductivity of the particles. Unfortunately, some instruments have a dead time in the pulse-processing
circuitry which can be significant and can correspond to an effective loss in the mass of the particles analysed. This
loss will depend on the total number of particles counted, but does not affect the size distribution obtained since the
same proportion of the count will be lost for all size classes.
Calibration should be checked on a regular basis to ensure that the change in the calibration constant is less than
1,0 %, or every time an orifice tube or an electrolyte solution is changed. See annex D for a method for calibration
of frequently used orifices.
6.11.2 Calibration procedure: microsphere calibration
Microspheres of narrow size distribution with a single mode, characterized by a variety of other methods, are
available. They should be traceable to the micrometre, to a Community Bureau of Reference (BCR), a National
Institute of Standards and Technology (NIST) or similar reference material. The calibration method used depends
on the assayed size parameter of the microspheres and the analyser used (contact the instrument manufacturers
for details). One method is to obtain a histogram (frequency) plot of the number of particles against channels of
equal width (on a linear scale). The size at the centre of the channel with the greatest number of particles
corresponds closely to the modal size of the calibration material if the distribution is symmetrical. If the distribution
is not symmetrical, the fractional channel position is calculated from the counts in the channels on either side of the
central channel. The calibration factor is the ratio of the modal size of the calibration material to the size as reported
on the instrument.
6.11.3 Calibration procedure: mass integration method (self-calibration)
6.11.3.1 A narrow size-range fraction of the material under test is prepared by sieving or a similar separation
method. At least 99 % of the mass of the particles should lie within a size range of no more than 10:1, so that all
can be measured using one orifice.
6.11.3.2 Using a balance weighing to an accuracy of 0,1 mg, a relative-density bottle, pipettes and the usual
particle-dispersion method, the immersed density � of the material in the elect
...
NORME ISO
INTERNATIONALE 13319
Première édition
2000-04-01
Détermination des répartitions
granulométriques — Méthode de la zone de
détection électrique
Determination of particle size distributions — Electrical sensing zone
method
Numéro de référence
ISO 13319:2000(F)
©
ISO 2000
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ISO 13319:2000(F)
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ii © ISO 2000 – Tous droits réservés
---------------------- Page: 2 ----------------------
ISO 13319:2000(F)
Sommaire Page
Avant-propos.iv
1 Domaine d'application.1
2 Termes et définitions.1
3 Symboles.1
4 Principe.2
5 Fonctionnement général .3
6 Modes opératoires.5
7 Calcul des résultats.11
8 Analyse .11
9 Validation.11
Annexe A (informative) Table des matériaux et des solutions électrolytiques .13
Annexe B (informative) Technique à deux ou plusieurs détecteurs.23
Annexe C (informative) Exemple d'étalonnage par intégration massique .25
Annexe D (informative) Étalonnage et surveillance des orifices fréquemment utilisés.27
Annexe E (informative) Fiches de données.28
Bibliographie .30
© ISO 2000 – Tous droits réservés iii
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ISO 13319:2000(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée aux
comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du comité
technique créé à cet effet. Les organisations internationales, gouvernementales et non gouvernementales, en
liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec la Commission
électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 3.
Les projets de Normes internationales adoptés par les comités techniques sont soumis aux comités membres pour
vote. Leur publication comme Normes internationales requiert l'approbation de 75 % au moins des comités
membres votants.
L’attention est appelée sur le fait que certains des éléments de la présente Norme internationale peuvent faire
l’objet de droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de
ne pas avoir identifié de tels droits de propriété et averti de leur existence.
La Norme internationale ISO 13319 a été élaborée par le comité technique ISO/TC 24, Tamis, tamisage et autres
méthodes de séparation granulométrique, sous-comité SC 4, Granulométrie par procédés autres que tamisage.
Les annexes A à E de la présente Norme internationale sont données uniquement à titre d’information.
iv © ISO 2000 – Tous droits réservés
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NORME INTERNATIONALE ISO 13319:2000(F)
Détermination des répartitions granulométriques — Méthode de la
zone de détection électrique
1 Domaine d'application
La présente Norme internationale fixe des lignes directrices pour le mesurage granulométrique de particules
dispersées dans une solution électrolytique, par la méthode de la zone de détection électrique. Elle n’aborde pas
les exigences spécifiques de mesure granulométrique de matériaux spécifiques. La méthode décrite dans la
présente Norme internationale mesure les volumes de particules et est applicable aux granulométries d’une
étendue comprise entre environ 0,6 �m et 1 600 �m.
2 Termes et définitions
Pour les besoins de la présente Norme internationale, les définitions et termes suivants s'appliquent.
2.1
temps mort
temps pendant lequel les dispositifs électroniques ne peuvent pas détecter de particules, en raison du traitement
des signaux d’une particule précédente
2.2
orifice
ouverture de faible diamètre, à travers laquelle la suspension est aspirée
2.3
zone de détection
volume de solution électrolytique dans, et autour de, l’orifice dans lequel est détectée une particule
2.4
volume d’échantillonnage
volume de suspension qui est analysé
3 Symboles
D diamètre d'orifice, en �m
K constante d'étalonnage de diamètre
d
K constante d’étalonnage de diamètre moyen
d
� écart-type de la constante d’étalonnage moyenne
K
d
m masse de l’échantillon dans le bêcher, en g
V volume de solution électrolytique dans lequel est dispersé m,enml
T
V volume d’analyse, en ml
m
�N nombre de comptages dans un intervalle de dimension i
i
�1
� masse de particules par volume de l’électrolyte qu’elle déplace, en g�ml
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ISO 13319:2000(F)
V volume moyen arithmétique pour un intervalle de dimension particulier i,enml
i
V volume de la particule obtenu à partir du seuil, ou limite de voie et unités des instruments; sans
i
étalonnage arbitraire au diamètre des particules (c’est-à-dire V = tIA,où t = niveau de seuil, I =courant
i
dans l'ouverture et A = facteur d'atténuation), en ml
x diamètre d'une sphère dont le volume est équivalent à celui de la particule, en�m
x , x , x valeurs de x correspondant aux points percentiles 50 %, 10 % et 90 % des répartitions de particules
50 10 90
déclassées inférieures en pourcentages cumulatifs, en�m
4Principe
La réponse, c’est-à-dire l’impulsion électrique générée au passage d'une particule par l’orifice, s’est révélée à la
fois expérimentalement et théoriquement proportionnelle au volume de la particule (voir Bibliographie). Une
suspension diluée de particules dispersées dans une solution électrolytique est agitée pour donner un mélange
homogène. Celui-ci est aspiré pendant ou après l’agitation, par un petit orifice ou une ouverture, dans une paroi
isolante. Un courant appliqué sur deux électrodes, placées de chaque côté de l’orifice, permet, par les
changements d’impédance électrique, de détecter les particules à mesure qu’elles traversent l’orifice. Les
impulsions générées par les particules sont amplifiées et comptées, et leur amplitude analysée. Après avoir
appliqué un facteur d’étalonnage, une répartition du nombre des particules en fonction du diamètre en équivalent
volume est obtenue. Cette répartition est en général convertie en pourcentage par masse par rapport à la
dimension granulométrique, lorsque le paramètre de dimension est exprimé sous forme de diamètre d’une sphère
de volume et de densité égaux à celui de la particule. Voir Figure 1.
Légende
1 Compteur volumétrique 6 Sortie
2 Soupape 7 Analyseur d’amplitude d’impulsion
3 Amplificateur d’impulsions 8 Suspension de particules agitées dans une solution électrolytique
4 Amplificateur d’impulsions de l’oscilloscope 9 Ouverture
5 Circuit de comptage 10 Arrêt/marche du compteur
Figure 1 — Diagramme illustrant le principe de la méthode de la zone de détection électrique
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ISO 13319:2000(F)
5 Fonctionnement général
5.1 Réponse
Si les particules sont sphériques, la réponse électrique est proportionnelle au volume des particules. Ceci s’est
également avéré pour les particules d’autres formes; cependant, la constante de proportionnalité (c’est-à-dire la
constante d’étalonnage de l’instrument) peut être différente. En règle générale, il convient que les particules aient
une faible conductivité par rapport à celle de la solution électrolytique, mais les particules conductrices peuvent
être mesurées.
5.2 Limites liées aux propriétés des particules
La limite inférieure de granulométrie de la méthode de la zone de détection électrique est généralement considérée
n’être restreinte que par le bruit thermique et électronique. Elle est normalement située à environ 0,6 μm, mais
dans des conditions favorables, une limite plus basse est possible. Il n’y a pas de limite supérieure théorique, et
pour les particules ayant une densité similaire à celle de la solution électrolytique, le plus grand orifice disponible
(normalement 2 000 μm) peut être utilisé.
Quand la masse volumique des particules est élevée, la limite supérieure de granulométrie est atteinte quand les
particules ne peuvent plus être maintenues en suspension homogène. Dans ce cas, la viscosité et/ou la densité de
la solution électrolytique doit être augmentée, par exemple en ajoutant du glycérol ou du saccharose.
L’étendue granulométrique pour un détecteur à un seul orifice est proportionnelle au diamètre de l’orifice, D.La
réponse s’est révélée dépendre de façon linéaire de D sur une étendue allant de 0,015 D à0,80 D (soit 1,5�mà
80�m pour un orifice de 100�m), bien que l’orifice ait tendance à s’obturer à des niveaux supérieurs à 0,60 D.
Cette étendue peut être augmentée en utilisant deux détecteurs ou plus (voir annexe B) mais dans la pratique, ce
mode opératoire peut être évité en sélectionnant soigneusement le diamètre d’un seul détecteur, de façon à avoir
une étendue acceptable.
La réponse de l’instrument dépend de la résistance électrique effective de la particule, qui est habituellement
élevée. Le mesurage des particules conductrices (par exemple des métaux, du carbone, du silicium et de
nombreux types de cellules et d’organismes, comme les globules sanguins) nécessite un temps de mise en œuvre
plus long. Les particules peuvent devenir électriquement translucides (c’est-à-dire donner une impulsion électrique
plus petite que ne l’indique leur volume) si une tension, généralement de 10 V à 15 V ou plus, est appliquée entre
les électrodes. Pour obtenir des résultats acceptables, une répartition est faite dans des conditions normales.
L’analyse est ensuite refaite en utilisant la moitié du courant et le double du gain (1/atténuation). Il est de règle que
les répartitions soient les mêmes. Si ce n’est pas le cas, il convient de recommencer la procédure en utilisant un
courant encore inférieur.
5.3 Effet du passage de particules coïncidentes
Des données idéales seraient obtenues si les particules traversaient l’orifice une par une, chaque particule
produisant ainsi une impulsion unique. Quand deux particules ou plus arrivent ensemble dans la zone de détection,
l’impulsion qui en résulte est complexe. Soit on obtient une grande impulsion unique, entraînant une perte de
comptage et l’enregistrement effectif d’une seule grosse particule, soit le comptage est correct mais la dimension
consignée de chaque particule est augmentée, soit certaines particules ne sont pas comptées. Ces effets altèrent
la répartition des particules obtenue, mais ils peuvent être minimisés en utilisant de faibles concentrations. Le
Tableau 1 montre les comptages par millilitre pour que la coïncidence soit de 5 % (soit environ une particule sur
vingt seulement est affectée). En règle générale, il convient que les comptages par millilitre soient toujours
inférieurs à ces valeurs données. Dans la mesure où il y a lieu que les répartitions granulométriques ne soient pas
fonction de la concentration, l’effet de la coïncidence peut être contrôlé en obtenant une répartition à une
concentration et en la comparant avec celle obtenue quand la concentration est diminuée de moitié. Pour ce
contrôle, refaire les dilutions jusqu’à ce que la réduction dans le comptage dans une voie ayant le plus grand
nombre, diminue proportionnellement à la dilution. Il est recommandé de toujours procéder ainsi lors de l’analyse
de répartitions granulométriques très étroites car c’est là où l’effet de la coïncidence est le plus sensible.
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ISO 13319:2000(F)
5.4 Temps mort
Dans certains instruments modernes, des routines d’analyse pour amplitudes d’impulsion sont utilisées pour traiter
les données. Dans la mesure où traiter chaque impulsion prend un temps fini, il est possible que l’analyseur ne
puisse pas compter les particules pendant un temps donné après réception d’une impulsion. Cela signifie que
lorsque le taux de comptage est relativement élevé, une proportion significative des comptages peut être perdue.
Comme le temps mort n’est pas fonction de l’amplitude des impulsions, la perte sera proportionnelle aux
comptages dans chaque voie, et n’affectera pas la répartition granulométrique. Cependant, si la concentration doit
être consignée ou si la méthode d’étalonnage par intégration massique (voir 6.11.3) doit être utilisée, l’effet peut
être limité au maximum en utilisant des suspensions diluées (par exemple à < 5 % de coïncidence) et en réglant
l’instrument de sorte que les impulsions dans les voies les plus basses ne soient pas comptées. Cela se fait en
obtenant d’abord une répartition des comptages et en observant le nombre de comptages par voie. Un résultat
type est indiqué à la Figure 2. En limitant les comptages dans la voie la plus basse à ceux indiqués en A, le temps
mort sera réduit au minimum.
En fonctionnement normal, ce temps mort ne causera aucune altération de la granulométrie puisque le risque de
ne pas être comptées sera le même pour toutes les particules, à condition qu’un grand nombre de particules, au
moins 100 000, soient comptées. Cependant, le temps mort affectera l’exactitude de la méthode d’étalonnage par
intégration massique (voir 6.11.3) là où il y aura une perte apparente de masse.
Les comptages dans les voies en dessous de A sont des comptages de bruits. Les comptages de particules réelles se trouvent
dans les voies plus élevées.
Figure 2 — Résultats types
5.5 Répétabilité des comptages
II a été montré que dans une analyse correcte, le nombre de comptages dans chaque voie est une variable
aléatoire qui suit la loi de Poisson. Cela signifie que l’écart-type d’un nombre de comptages N avoisine N .Ainsi,
dans une série de répétitions, le nombre de comptages dans une voie, N , N , N , etc. qui produit un comptage
i,1 i,2 i,3
moyen N avec un niveau de confiance de 95 %, en règle générale, les comptages répétés N se situent dans la
i i,n
gammeNN� 19, 6 ; c'est-à-dire que si le comptage N est de 100 000, l'incertitude est de � 619. Si pour vingt
ii i
analyses répétées, plus d’une se situe hors de cette gamme, il convient de réexaminer le mode de préparation des
échantillons (voir 6.7). Ce contrôle statistique peut être effectué sur des voies uniques, des groupes de voies, ou
sur le comptage total des particules.
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ISO 13319:2000(F)
6 Modes opératoires
6.1 Situation des instruments
Il est recommandé de placer l’instrument dans un environnement propre, exempt d’interférences électriques et de
vibrations excessives. Si des solvants organiques doivent être utilisés, il convient d’assurer une bonne ventilation
du secteur.
6.2 Linéarité du système détecteur/amplificateur
La linéarité du système détecteur/amplificateur peut être vérifiée en utilisant trois suspensions de particules
monodispersées de diamètre certifié. Dans une solution électrolytique adaptée, l’instrument est étalonné avec des
particules d’environ 0,3 D (voir 6.11.2). Des microsphères de deux autres dimensions sont ensuite ajoutées à la
suspension (une de dimension d'environ 0,2 D et une d'environ 0,5 D). La suspension est analysée de nouveau et
la dimension correspondant à ces crêtes supplémentaires doit correspondre à la dimension indiquée des particules
à 5 % près.
6.3 Linéarité du système de comptage
La linéarité du système de comptage peut être contrôlée en effectuant trois comptages à une concentration
arbitraire. La concentration est ensuite réduite et trois autres comptages obtenus. Le rapport de la moyenne des
comptages est en règle générale le même que celui de la dilution. Si la concordance ne se situe pas à 5 % près, il
convient de refaire le contrôle en comparant les deux dilutions les plus faibles (la coïncidence peut empêcher
d’obtenir le comptage exact si la concentration est trop élevée). En règle générale, les analyses ultérieures sont
effectuées à la dilution donnant les meilleurs résultats.
6.4 Volume V de la suspension analysée
m
Si les concentrations des particules doivent être déterminées ou si la méthode d’étalonnage par intégration
massique doit être utilisée (voir 6.11.3), il est nécessaire de vérifier le volume V de la suspension analysée, qui
m
est habituellement garanti uniquement à une valeur dosée par le fabricant. Il convient de connaître la valeur du
volume analysé. À l’aide d’une suspension de particules, à un niveau de comptage statistiquement valable
(voir 6.3), mesurer trois fois le comptage total des particules avec ce volume. Passer à un autre volume d’analyse
et effectuer au moins trois fois les comptages totaux de particules. Le rapport du nombre total de comptages sera
le rapport entre le volume garanti et le volume sélectionné. Il convient de consigner tous les comptages.
6.5 Choix de la solution électrolytique
Il est recommandé de sélectionner une solution électrolytique dans laquelle l’échantillon est insoluble. Il y a lieu
que la solution ne dissolve, ne flocule, ou ne provoque aucune réaction, ni ne gêne de toute autre manière l’état de
dispersion de l’échantillon pendant le temps de mesure, en général jusqu’à 5 min.
Les particules insolubles dans l’eau peuvent être analysées dans des électrolytes aqueux, comme une solution
d’orthophosphate de sodium hydraté à 50 g/l, ou une solution de chlorure de sodium à 10 g/l. Les particules
solubles dans l’eau peuvent souvent être analysées dans une solution de chlorure de lithium à 50 g/l dans du
méthanol, ou dans une solution de thiocyanate d’ammonium à 50 g/l dans de l’isopropanol. Voir annexe A pour les
autres solutions recommandées pour de nombreux matériaux communs.
6.6 Préparation de la solution électrolytique
Il est recommandé de bien filtrer avant utilisation la solution électrolytique à l’aide d’un filtre à diaphragme d’une
grosseur de pores inférieure au diamètre de la plus petite particule mesurée, car il est essentiel que le comptage
de fond soit aussi bas que possible. Il est recommandé de rincer au préalable toute la verrerie et tous les autres
appareils utilisés avec de la solution électrolytique filtrée. Les comptages de fond ne dépassent pas en règle
générale les valeurs données dans le Tableau 1 ni ne donnent un volume équivalent total dépassant 0,1 % du
volume total des particules ultérieurement mesurées dans le même volume d’échantillonnage.
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ISO 13319:2000(F)
Tableau 1 — Comptages de fond et coïncidence à 5 % pour les diamètres types d’orifice
c
Diamètre Volume Comptages
Comptages pour
a b
d'orifice
d'analyse de fond coïncidence à 5 %
D
V N
m
�m ml
1 000 2 2 80
560 2 10 455
400 2 25 1 250
280 2 75 3 645
200 2 200 10 000
140 2 600 29 150
100 0,5 400 20 000
70 0,5 1 200 58 500
50 0,05 300 16 000
30 0,05 1 500 74 000
20 0,05 5 000 250 000
a
Pour d'autres volumes d'échantillons, utiliser les valeurs au prorata.
b
Comptages maximaux recommandés.
10
41� 0 V
c
m
Calculés à l'aide de l'équation
N �
3
D
6.7 Préparation et dispersion recommandées des échantillons
6.7.1 Généralités
Un dispersant est en règle générale sélectionné parmi les recommandations de l'ISO 14887 ou l'annexe A.
6.7.2 Méthode 1: à l’aide d’une pâte
3
L’échantillon est généralement subdivisé jusqu'à obtenir environ 0,2 cm . Si l’échantillon est sous forme de poudre,
il convient de la travailler et la pétrir doucement avec une spatule souple et quelques gouttes d’un dispersant
adapté pour briser les agglomérats. Une masse d’environ 20 mg à 50 mg de la pâte est transférée dans un bêcher
à fond arrondi et diluée avec du dispersant, puis avec quelques gouttes de la solution électrolytique. Le bêcher est
presque rempli de solution électrolytique et placé dans un bain à ultrasons de faible puissance pendant 1 min, en
remuant de temps en temps. La Figure 3 donne un modèle approprié de bêcher d’une capacité de 400 ml avec
déflecteur. Le bain à ultrasons est en règle générale de l’ordre de 50 W à 100 W, 60 kHz à 80 kHz, et il est
recommandé d’utiliser un chronomètre pour assurer une technique de dispersion reproductible.
NOTE L’utilisation de bains et sondes, mélangeurs et mixeurs ultrasoniques à forte énergie peut provoquer à la fois une
agglomération et une fracture des particules.
S’il n’est pas nécessaire que l’échantillon soit dispersé complètement, il peut être ajouté à la solution électrolytique
et au dispersant tout en agitant.
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ISO 13319:2000(F)
Figure 3 — Exemple de bêcher avec déflecteur et agitateur
6.7.3 Méthode 2: autre méthode applicable aux particules de faible densité de moins de 50����m
L’échantillon est en règle générale subdivisé pour obtenir un échantillon d’environ 1 g qui est mélangé au
dispersant et ajouté à l’électrolyte et à la solution. Le bêcher (voir Figure 3) contenant la suspension est ensuite
placé dans un bain à ultrasons pendant environ 45 s. Après avoir bien agité cette suspension mère, 5 ml en sont
retirés à l’aide d’une pipette et ajoutés à environ 400 ml de solution électrolytique, puis placés dans le bain à
ultrasons pendant 15 s supplémentaires. Avec cette méthode, il est important qu’au moins deux échantillons soient
retirés de la suspension mère et analysés, pour garantir la répétabilité de l’échantillonnage aliquote et de l’analyse.
6.7.4 Suspensions et émulsions
Les suspensions et les émulsions peuvent être diluées en ajoutant lentement la solution électrolytique. Pour éviter
tout «choc de dilution», les émulsions d’huile dans l’eau peuvent être diluées pour commencer avec de l’eau
distillée ou déminéralisée.
6.7.5 Vérification de la dispersion
Un petit échantillon de la dispersion est placé sur une lame porte-objet d’observation au microscope optique et
utilisé afin de vérifier le degré de dispersion et estimer l’étendue granulométrique des particules.
6.8 Choix d’orifice(s) et volume(s) d’échantillonnage
À partir de l’examen au microscope (6.7.4), estimer le diamètre des plus grosses particules présentes.
Choisir un orifice pour l’analyse granulométrique de sorte que le diamètre des particules les plus grosses à
analyser soit inférieur d’environ 50 % au diamètre de l’orifice, et ceci afin de réduire la possibilité d’obturation de
l’orifice. S’il y a une proportion considérable de l’échantillon en dessous de la limite granulométrique inférieure de
cet orifice (1,5 % de son diamètre), un deuxième et éventuellement un troisième orifice plus petits seront
nécessaires (voir annexe B).
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ISO 13319:2000(F)
Sélectionner un volume d’échantillonnage convenable en se référant au Tableau 1. Il peut être nécessaire
d’analyser un certain nombre de ces volumes d’échantillonnage pour accumuler un nombre total de particules
valable statistiquement, par exemple environ 100 000 [soit une précision de� 619 (voir 5.5) ou supérieure à �1%].
Le fait de compter moins de particules réduira la précision, mais ceci peut être nécessaire en utilisant des orifices
plus grands ou en effectuant des études de contamination.
6.9 Nettoyer un orifice obturé
Les orifices en dessous de 100 μm de diamètre peuvent être obturés par des particules étrangères, en particulier si
des précautions ne sont pas prises pour assurer une manipulation propre, un filtrage soigneux et un bon rinçage
des bêchers et équipements associés. Une obturation se voit facilement au moyen de l’optique de visée fourni
avec l’analyseur.
Une obturation partielle peut être indiquée par des durées d’écoulement différentes pour le même volume dosé. Il
est possible de retirer les obturations automatiquement ou par l’une des techniques suivantes:
a) rinçage: inverser le sens d’écoulement par l’orifice peut suffire à dégager une obturation;
b) ébullition: il est possible d’utiliser l’effet de la chaleur du courant pour amener une ébullition et dégager
l’obturation. Ceci se fait en utilisant un fort courant dans l’orifice;
c) brossage: il est souvent possible de brosser les particules pour les détacher de l’orifice en utilisant une petite
brosse souple de première qualité et avec des poils coupés court. Il convient de faire attention à ne pas
endommager l’orifice;
d) pression d’air;
e) nettoyage par ultrasons: le tube de l’orifice étant rempli de solution électrolytique, plonger l’extrémité dans un
bain à ultrasons de faible puissance pendant environ 1 s. Répéter cette opération autant de fois que
nécessaire. Cette méthode est très efficace mais il convient de faire particulièrement attention car il est
possible d’endommager l’orifice.
AVERTISSEMENT — Il est recommandé de ne pas utiliser cette méthode pour les orifices de 50��mou
��
moins.
6.10 Stabilité de la dispersion
Une fois le meilleur orifice installé, et la suspension préparée, sécher l’extérieur du bêcher et le placer sur le
support échantillon de l’instrument. Ajuster l’agitateur pour un effet maximum sans créer de tourbillon qui causerait
des bulles.
La stabilité de la dispersion pendant l’analyse est ensuite vérifiée. Une analyse granulométrique complète est faite
dès que possible après dispersion; la suspension est ensuite agitée pendant 5 min à 10 min et la suspension est
analysée de nouveau. Des comptages cumulatifs sont consignés à des niveaux de dimensions proches de 30 % et
5 % du diamètre d’orifice (appelé x et x respectivement). Des changements dans les comptages supérieurs à
max min
ceux attendus des statistiques, soit N , indiqueront que la dispersion n’est pas stable. Le Tableau 2 précise
certaines causes possibles.
Dans tous les cas indiqués dans le Tableau 2, sauf le premier cas, il convient d’essayer une combinaison différente
dispersant/solution électrolytique, et de vérifier de nouveau la dispersion.
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ISO 13319:2000(F)
Tableau 2 — Exemples de phénomènes de dispersion supposés
Changement dans le comptage Suggestion
x x
max min
pas de changement pas de changement dispersion stable
augmentation augmentation cristallisation, précipitation
diminution diminution dissolution
diminution augmentation réduction des dimensions, défloculation
augmentation diminution floculation, agglomération
diminution pas de changement sédimentation de grosses particules
6.11 Étalonnage
6.11.1 Généralités
Les
...
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