Download - L6_040214
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Powder Characterizations
Characterizations
Physical
Characteristics
Chemical
Composition
Phase
Composition
Surface
Characteristics
1. Particle size anddistribution
2. Particle shape
3. Degree of
agglomeration
4. Surface area
5. Density andporosity
6. Flow properties
and granulation1. Major elements
2. Minor elements
3. Trace elements
(AAS, AES, XRF)
Crystal structure and
phase
composition
1. Surface structure
(LEED, STM, AFM)
2. Surface
composition
(AES, XPS, ESCA,
SIMS)
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Physical Characterizations of Powder
Types of Particles
Primary particleSmallest unit in
the powder with
a clearly defined
surface/isolated
porosity
Agglomerates
Cluster of
primary particles
held together by
surface force
Types: Soft and
Hard
ParticlesSmall units that
move as a
separate entity
(Coarse particle
1-100 mm)
Granules
Large
agglomerates(Dimension 100-
1000 mm)
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Physical Characterizations of Powder
Types of Particles
Flocs
Cluster of
particles in a
liquid
suspension
Colloids
Finely divided
phase in a fluid
(Brownian
motion, negligible
sedimentation
under normalgravity (1 nm1
mm)
Aggregates
Coarse
constituent in a
mixture (pebbles
in concrete)
(1 mm)
Definition of Particle Size
Stokes diameter
Diameter of the sphere calculated fromStokes law
Projected area diameterprojected area of the particle under
microscope
Feretsdiameter/Martins diameterLinear dimension
measured parallel to some fixed direction
(Attached sheet)
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Physical Characterizations of Powder
Methods for Measurement of Particle Sizes
Method Range (m)
Microscopy
Optical 1
SEM 0.1
TEM 0.001
Sieving 2010,000
Sedimentation 0.1100
Coulter counter 0.5400
Light Scattering
Scattering intensity 0.11000
Brownian motion 0.0051
X-ray line broadening 0.1
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Physical Characterizations of Powder
Martins Diameter (XM )- length of a line that
bisects the area of the particle image
Ferets Diameter (XF )- distance between two
tangents on opposite sides of the particle,
parallel to some fixed direction
Projected Area Diameter (XPA )- diameter of a
circle having the same area as the two-
dimensional image of the particle
Perimeter Diameter (XC )- diameter of the circle
having the same circumference as the perimeterof the particle
The longest dimension is equal to the maximum
value of Ferets diameter
Measurement of Particle Size by Microscopy
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Physical Characterizations of Powder
Methods for Measurement of Particle Sizes
Method Range (m)
Microscopy
Optical 1
SEM 0.1
TEM 0.001
Sieving 2010,000
Sedimentation 0.1100
Coulter counter 0.5400
Light Scattering
Scattering intensity 0.11000
Brownian motion 0.0051
X-ray line broadening 0.1
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Physical Characterizations of Powder
Measurement of Particle Size and Size Distribution by Sieving
Mesh size= the number of wires per
linear inch of the sieve screen, which is
the same as the number of square
apertures per inch.
If mesh number = M, aperture width = a,
wire diameter = w, and the open area =
A, then:
wa
M
1
wM
a 1
2
2
2
)()(
Mawa
aA
Problem: Find out the wire diameter
and open area of a 400 mesh sieve
with an aperture of 38 mm?
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Physical Characterizations of Powder
Methods for Measurement of Particle Sizes
Method Range (m)
Microscopy
Optical 1
SEM 0.1
TEM 0.001
Sieving 2010,000
Sedimentation 0.1100
Coulter counter 0.5400
Light Scattering
Scattering intensity 0.11000
Brownian motion 0.0051
X-ray line broadening 0.1
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Physical Characterizations of Powder
Measurement of Particle Size and Size Distribution by Sedimentation
Stokess Law,
avF 6F = Frictional force
acting on the particle,
= Liquid viscosity,
a = particle radius
v = terminal velocity
Stokess Equation,
2/1
18
gddvxLs
x = diameter of the
particle with sphere
shape,
ds = particle densitydL = liquid density
For non spherical particle,
Limitations
1. Holds good for laminar (non-turbulent) flow
2. No inter-particle collision
3. No interactions between the particles
STKxx
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Laminar to turbulent flow occurs at some critical velocity,
2.0~
xd
N
v L
R
c
2.0
xvdL
2.0xvdL
NR= Reynolds Number
Laminar Flow
Turbulent Flow
The particle size distribution is determined by measuring
the change in concentration (or density) of the suspension as a function
of time, height along the suspension, or both.
A light beam or an x-ray beam is projected at a known height through a
glass cell containing the suspension.
The intensity of the transmitted beam is measured by a photocell or an
x-ray detector located at the opposite side.
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The intensity I of thetransmitted beam will increase as,
)exp(0 KACyII I0= Intensity of the incident beam
K = Extinction coefficient
A = Projected area per unit mass of the
particle
C = Concentration by mass of the particle
y = Optical path length through the
suspension
The particle size distribution [e.g., the cumulative mass percent finer
(CMPF) versus the Stokes diameter] is deconvoluted from the measured intensityratio, I/Io, coupled with Stokes Eq.
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Physical Characterizations of Powder
Methods for Measurement of Particle Sizes
Method Range (m)Microscopy
Optical 1
SEM 0.1
TEM 0.001
Sieving 2010,000
Sedimentation 0.1100
Coulter counter 0.5400
Light Scattering
Scattering intensity 0.11000
Brownian motion 0.0051
X-ray line broadening 0.1
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Physical Characterizations of Powder
Measurement of Particle Size and Size Distribution by Coulter Counter
As a particle passes through the orifice,
it displaces an equivalent volume of the
electrolyte and causes a change in the
electrical resistance, the magnitude of which
is proportional to the volume of the particle.
The changes in resistance are converted to
voltage pulses, which are amplified, sized,
and counted to produce data for the particle
size distribution of
the suspended particles.
Since the number and volume of the
particles are measured in this technique, the
particle size distribution will consist of the
CNPF (or CNPL) versus the volume diameter
xV
Disadvantage
Blocking of the orifice by bigger particle