Particle size measurement

長庚化材系郭修伯

Nano scale

1 nm ~ 10 hydrogen atoms

Scales

Rain 1 mm - 1 cm

Drizzle 100 m - 1 mm

Fog 1 m - 100 m

Smog < 1 m

Human scales...

Human hair (~70 m)

Human blood cell (~7.5 m)

Nanotechnology

Nanostructured materials at least one dimension falling in nanometer

scale nanoparticles (including quantum dots),

nanorods, nanowires, thin films bulk materials made of nanoscale building

blocks or consisting nanostructures

Fabrication

Growth media vapor phase

growth liquid phase

growth solid phase

formation hybrid growth

Forms nanoparticles nanorods thin films nanostructured

bulk materials

Nanotechnology

Size ? Au 一般融點 1053°C ， 20 nm 以下，明顯

下降， 3 nm 約 500 °C “size” does not matter, the “effect” matters Technologies

– formation, measurement– classification, dispersion, mixing, tranportation

usually < 100 nm

化妝品 - 肌膚修飾粉底

數 micron ~ 數十 nm 均勻粒子

薄片狀 (nanometer-repair)

透明感

100 ~ 200 nm 脂質人工膜 保溼效果 ( 徐放效果 )

雲母或滑石 25 ~ 90 nm 氧化亞鉛 或二

氧化鈦 coating 1 ~ 10 nm silica coating

醫藥

導引投藥 carrier 磁性粒子球 (~ 10 nm)

徐放性 持續效果 防止忘記服藥 正確劑量 防止血液中特定藥物濃度

急速上升

經口徐放性劑型

粉末吸入劑型

氣喘： 支氣管末維持數 micron 以下粒子分散狀態 各器官捕捉 binderless 造粒法

– carrier ( 數十 micron)– 藥劑 ( 數 micron)

Fig 1.6

Sick house

溶劑 + 氣密窗 光觸媒 ( 主要是 TiO2)

中空 ceramics 粒子

隔熱塗料 太陽光 3% 紫外光， 47% 可見光， 50% 紅外光

heat-island 防止

Fig 1.14

Fig 1.15

Particle size

Polydisperse and monodisperse 構成粒子的大小程度。嚴格而言，定義的單

位為長度（也有用 mesh ） 包含幾何徑，相當徑，有效徑。應用顯微鏡

等其他影像法所測得的為幾何徑和相當徑。 幾何徑包含長軸徑，短軸徑，定方向徑等。定方

向徑又可分為 Feret 徑， Martin 徑及定方向最大徑 (Krummbein) 。

Particle size

相當徑包含周長圓相當徑，體積球相當徑等。 equivalent-volume sphere diameter,

equivalent-surface sphere diameter,

equivalent-projected-area circle diameter,

31

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v

d v

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S

d s

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A

d A 2

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dd sA

Particle size

有效徑為粒子實際應用時的粒子相當徑。包含Stokes 徑， Allen 徑及 Newton 徑。

The Stokes diameter: the diameter of a sphere with the same settling velocity as the particle.

The Stokes diameter and the equivalent-volume sphere diameter are related:

where c is the hydrodynamic resistance of the particle. For a non-sphere particle, dst is always greater than dv.

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Vd

p

tst

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dd vst

Particle size

The choice of equivalent diameter depends on the use to which the data are put. If the efficiency of an inertial separating device such as cyclone is required, it is appropriate to use Stokes diameter, since this best describes the behaviour of particles suspended in a fluid when inertial effects are dominated.

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Methods

The ultimate requirement is for a portable on-line instrument having a fast response and producing the size distribution of the particle diameter which is most closely related to the phenomena under investigation.

Sieve (JIS 8801; ASTM E1158T; and BS 410) (~ 5 m)

Mass distribution Sieve diameter: particles are sorted by their

two smallest dimensions only. Generally used for particles in the size range

53 to 3350 microns. It is difficult to sieve fine powders (~ 75

microns) Errors can occur due to "blinding" or sieve

blocking, particle breakage and mesh stretching caused by overloading.

Microscopy

Number distribution The diameter obtained is the diameter of

the circle of equivalent projected area, dA.

For dA > 0.8 micron, optical microscopy is possible.

Counting numbers

Light scattering

The incident light energy may be deflected and the deflection process is referred as "scattering".

The scattered light-intensity, I(θ), is defined as the amount of electromagnetic energy which crosses unit area perpendicular to the flow per unit time at angle θ to the incident beam.

At a distance R in the direction θ from a spherical particle illuminated with unpolarised light of intensity I0, the scattered intensity is:

(Hinds, 1982)

where i1 and i2 are the Mie intensity parameters and are functions of refractive index, size parameter, and scattering angle.

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Particle Size Measurement

d << λ Rayleigh scattering theory d ~ λ Mie theory d >> λ Fraunhofer and Anomalus theory

Light scattering

Three basic types: single particle counters, Fraunhofer scattering instruments, and extinction meters

Single particle counter: the forward-scattered light is collected by a lens (or a mirror), and focused onto a photomultiplier where it is converted into a voltage pulse. Successive pulses are classified by peak height and are used to construct the size distribution by number.

Fraunhofer scattering instruments: also known as "field scattering" instruments. The angular distribution of the forward-scattered light intensity from a multiparticle "field" was converted into a (volume) size distribution. The diffraction sizing.

Extinction meters: used in situ to follow particulate emissions to atmosphere from stacks. They can only give a measure of total loading or an average particle diameter, rather than a size distribution.

Light scattering

For small particles (say d < 0.05 micron), the simplified Rayleigh scattering theory can be used: I(θ) is proportional to .

For large particles much larger than the wavelength (say d >≈ 2 micron), the scattered light intensity can be approximated by Fraunhofer diffraction theory.

4

6

d

Mie theory

A complete formal solution to Maxwell's equations for the incident light wave, the wave inside the particle, and the scattered wave, subject to a set of boundary conditions at the particle surface. Complicated!

Light scattering

The forward-scattered light is less sensitive to particle refractive index and shape and hence used for most commercial application.

Even for spherical aerosols of known refractive index, theoretical response prediction is tedious, so it is usual practice to calibrate each instrument in the factory using mono-sized polystyrene latex spheres (refractive index = 1.59) and to incorporate a calibration device into the instrument.

Light scattering

Accuracy: Single particle light scattering counters are very sensitive to shape and refractive index effects and must be precalibrated. Instruments based on Frauhofer diffraction are rather less sensitive to refractive index and shape effects (used for 1.6 ~ 4 microns)

Concentration: Single particle light scattering counters require special dilution systems for measuring particles at high concentrations. Instruments based on Frauhofer diffraction are subject to signal-to-noise ratio problems at low concentrations.

Extinction instruments measure the intensity of the light which is not scattered out of the beam. If the particles are sufficiently coarse, and average measure of the suspension properties may be obtained. They cannot provide more than some indication of either particle concentration or particle size.