Transcript Particle size measurement 長庚化材系 郭修伯 Nano scale 1 nm ~ 10 hydrogen atoms.

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
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Nanostructured materials
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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
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Growth media
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vapor phase
growth
liquid phase
growth
solid phase
formation
hybrid growth
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Forms
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nanoparticles
nanorods
thin films
nanostructured
bulk materials
Nanotechnology
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Size ?
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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
–
–
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formation, measurement
classification, dispersion, mixing, tranportation
usually < 100 nm
化妝品 - 肌膚修飾粉底
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數 micron ~ 數十nm 均
勻粒子
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薄片狀 (nanometerrepair)
透明感
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100 ~ 200 nm 脂質人工膜
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保溼效果 (徐放效果)
雲母或滑石
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25 ~ 90 nm 氧化亞鉛 或二氧
化鈦coating
1 ~ 10 nm silica coating
醫藥
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導引投藥
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carrier
磁性粒子球 (~ 10 nm)
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徐放性
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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
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氣喘：
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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
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溶劑+氣密窗
光觸媒 (主要是 TiO2)
中空ceramics粒子
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隔熱塗料
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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。
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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
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相當徑包含周長圓相當徑，體積球相當徑等。
1
equivalent-volume sphere diameter,
 6v  3
dv   
 
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equivalent-surface sphere diameter,
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equivalent-projected-area circle diameter,
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S
d A  ds   
 
1
2
S
ds   
 
1
 4A 
dA  

  
2
1
2
 18Vt 

d st  
 (   ) g 
 p

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1
2
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.
 3d
d st  
 c

3
v




1
2
The Stokes diameter and the equivalent-volume sphere
1
diameter are related:
 18V  2
t

d st  
 (   ) g 
 p



where c is the hydrodynamic resistance of the particle.
For a non-sphere particle, dst is always greater than dv.
 18Vt 

d st  
 (   ) g 
 p


1
2
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.
Methods
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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)
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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
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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
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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:
I 2 (i  i ) (Hinds, 1982)
I ( ) 
0
1
2
8 R 2
2
where i1 and i2 are the Mie intensity parameters and are functions
of refractive index, size parameter, and scattering angle.
Particle Size Measurement
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d << λ Rayleigh scattering theory
d ~ λ Mie theory
d >> λ Fraunhofer and Anomalus theory
Light scattering
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Three basic types: single particle counters, Fraunhofer
scattering instruments, and extinction meters
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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
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For small particles (say d < 0.05 micron), the
simplified Rayleigh scattering theory can be
used: I(θ) is proportional to .
6
d
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4
For large particles much larger than the
wavelength (say d >≈ 2 micron), the
scattered light intensity can be approximated
by Fraunhofer diffraction theory.
Mie theory
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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
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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
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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.