Page 34 - Book Hosokawa Nanoparticle Technology Handbook

1.2 PARTICLE SIZE FUNDAMENTALS
principles unless the particles are spherical. Specific measurements. The particles measured based on
surface area of powder or equivalent-specific surface these different principles should, at least, show the
diameter is well applied to the evaluation of nanopow- same diameter as far as they are spherical particles.
ders. However, in this case, the particles should not be Therefore, we are now preparing spherical reference
porous. Besides, the method cannot be applied to get particles [3, 4]. Various mono-disperse spherical par-
particle size distribution [1, 2]. ticles are available from The Association of Powder
Process Industry and Engineering (APPIE, Japan)
[5, 6]. However, they are not suitable for the calibra-
1.2.2 Measuring methods
tion of such equipments for the measurement of par-
As discussed in the preceding section, geometric size is ticle size distribution for the following reasons [7]:
obtained in the microscopic measurements, and equiv-
alent size is applied in the measurements by practically 1. Even if the principle is the same, different equip-
available instruments such as those based on laser dif- ments have different feeding system, different
fraction and scattering, dynamic light scattering, differ- transportation system and different dispersion
ential mobility analysis, and so on. The equivalent size system. Therefore, particle fraction detected in a
obtained by these instruments is practical but does not certain size interval may differ depending on the
give a value directly connected to the unit of length.
The items discussed in the ISO relating to the par- equipment through size-dependent deposition,
ticle size measurements are as follows: imperfect dispersion and size-dependent segre-
gation.
1. ISO 13317: Determination of particle size dis-
2. There may be various calculation software for
tribution by gravitational liquid sedimentation
the transformation of the measured data to par-
methods (This ISO corresponds to JIS Z 8820).
ticle size distribution.
2. ISO 13318: Determination of particle size dis-
3. Number of particles sampled, sample size, in the
tribution by centrifugal liquid sedimentation
measurement may differ for each measuring
methods (JIS Z 8823).
system. If the sample size is not large enough,
3. ISO 13319: Determination of particle size dis-
both the mean diameter and the size distribution
tribution – Electrical-sensing zone method.
cannot be correctly obtained [8, 9].
4. ISO 13320: Particle size analysis–Laser dif-
fraction methods (JIS Z 8825). In the ISO 13320 (1999), laser diffraction, it is
5. ISO 13321: Particle size analysis – Photon cor- recommended that equipment should be tested using
poly-disperse reference particles whose particle size
relation spectroscopy (JIS Z 8826).
is distributed over one decade. Reference particles for
6. ISO 13322: Particle size analysis –Image
covering nano-range is not yet available. However,
analysis methods. MBP 1–10 for 1–10 m and MBP 10–100 for
7. ISO 13323: Determination of particle size distri- 10–100 m, spherical transparent particles, are avail-
bution – Single particle light interaction methods. able from APPIE. Particle size analyzers should at
least be calibrated by use of these spherical reference
8. Particle size analysis – Dynamic light scattering
particles.
(DLS).
Through the calibration using the reference parti-
9. Determination of particle size distribution – cles, equivalent size obtained by each instrument is,
Differential electrical mobility analysis for for the first time, connected to the unit of length. In
aerosol particles (DMA). other words, measured value obtained by the meas-
urement other than microscopy can get traceability
10. Particle characterization by acoustic methods –
only through the calibration with reference particles.
Ultrasonic attenuation spectroscopy.
It is very tedious to measure a great number of parti-
11. Focused beam techniques. cles by electron microscopy. Therefore, in practice,
sedimentation method, standard sieves and electrical
Some of these methods can be applied to the measure- sensing zone method are admitted as definitive meth-
ments of nanoparticles. Japanese industrial standard ods to the certification of reference particles [5].
will also cover the methods in keeping pace with ISO.
However, this is only for the sake of convenience.
The purpose for using the reference particles is
1.2.3 Key points in the measurements – Reference listed as follows [10]:
particles for calibration 1. Calibration of equipments for the particle size
Important point is that these particle sizes take measurement,
different values depending on the principles of the 2. Verification of measurement procedure,
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