Image Analysis: Evaluating Particle Shape

Image Analysis: Evaluating Particle Shape
Image Analysis: Evaluating Particle Shape
Jeffrey Bodycomb, Ph.D.
HORIBA Scientific
www.horiba.com/us/particle
© 2011 HORIBA, Ltd. All rights reserved.
Why Image Analysis?
„ Verify/Supplement diffraction results (orthogonal
technique)
„ Replace sieves
„ Need shape information, for example due to
importance of powder flow
These may have the same size (cross section), but
behave very differently.
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Why Image Analysis?
„ Crystalline, acicular powders needs more than
“equivalent diameter”
We want to characterize a needle by the
length (or better, length and width).
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Why Image Analysis
„ Pictures: contaminants, identification, degree of
agglomeration
„ Screen excipients, full morphology
„ Root cause of error (tablet batches), combined
w/other techniques
„ Replace manual microscopy
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Why Shape Information?
„Evaluating packing
„Evaluate flow of particles
„Evaluate flow around particles
„Retroreflection (optical properties)
„Properties of particles in aggregate
(bulk)
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Effect of Shape on Flow
„ Yes, I assumed density doesn’t matter.
„ Roundness is a measure based on particle
perimeter.
θc
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Major Steps in Image Analysis
Image Acquisition
and enhancement
Object/Phase
detection
Measurements
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Two Approaches
Dynamic:
particles flow past camera
1 – 3000 microns
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Static:
particles fixed on slide,
stage moves slide
0.5 – 1000 microns
2000 microns w/1.25 objective
Size Parameters -> Shape Parameters
Shape parameters are often calculated using size measures
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Size Parameters
„Feret
zMax (length)
zPerpendicular to Max (width)
zMin (width)
zPerpendicular to Min (main length)
„Area
zCircular Diameter
zSpherical Diameter
„Perimeter
„Convex Perimeter
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Ferets
„ Size as measured with a caliper
„ Result depends on orientation of caliper
⊥ to Max
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Max
Min
z Min
z Max
z Perpendicular to Min
z Perpendicular to Max
⊥ to Min
Area (Circular Diameter)
„ Count pixels to find
area of particle
„ Convert to circle
with equivalent area
same AREA
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2
Area
π
Diameter
Perimeter, Convex Perimeter
„Perimeter follows exact contours of
object
„Convex perimeter is like a rubber band.
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Shape Descriptors
„aspect ratio
„roughness
„roundness
„sphericity
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Shape Using a Chart
Krumbein, Journal of Sedimentary Petrology,
vol 11, no 2, pp 64-72, plate 1, August, 1941
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A different chart
„Compare particles to a chart like the
one below.
Overall
shape
like a
sphere
Round corners
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Aspect Ratio
„ Length of longest Feret over Length of
shortest Feret
„ Longest Feret over Feret perpendicular to
longest Feret
„ Feret perpendicular to shortest Feret over
shortest Feret
„ Or their reciprocal!
„ Nice measure of deviation from roundness.
Is not profoundly affected by bumps on
particle surface.
„ Measures “large scale shape”
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Aspect ratios of square
1
Fe Min is 1
1
Fe Max is diagonal: 1.414
Perp to Fe Max is diagonal: 1.414
Fe Max / Fe Min = 1.414/1 = 1.414
Fe Max / Perp to Fe Max = 1.414/1.414 = 1
Perp to Fe Min / Fe Min = 1/1 = 1
© 2011 HORIBA, Ltd. All rights reserved.
Salt Shape in Aluminum Foam
„ NaCl is used to manufacture
aluminum foams as a filler.
The NaCl is subsequently
dissolved away to leave a
porous structure.
„ The shape and size of the
NaCl affects the foam
structure and the final
properties of the foam.
Image courtesy of Wikimedia Commons User Stehfun
C. Gaillard, J. F. Despois and A. Mortensen
Processing of NaCl powders of controlled size and shape for the microstructural tailoring of aluminium foams
Materials Science and Engineering A
Volume 374, Issues 1-2, 15 June 2004, Pages 250-262
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NaCl Shape
HORIBA Application Note AN189: size and Shape Analysis of Salt using Dynamic Image Analysis
© 2011 HORIBA, Ltd. All rights reserved.
Glass beads for reflective pavement marking
„ Beads must be round to reflect light back to driver.
„ Check aspect ratio of each particle, fail if too many
particle have a value that is too low.
Aspect ratio 0.5051
Aspect ratio 0.9660
HORIBA Application Note AN140: Particle size and Shape analysis of glass beads for pavement markings
© 2011 HORIBA, Ltd. All rights reserved.
Acetaminophen (API)
© 2011 HORIBA, Ltd. All rights reserved.
Roughness
„ Jaggedness of
edges
„ Short scale.
Roughness is
sensitive to bumps
on surface
„ As surface has more
concavities, the
convex perimeter
increases and
therefore roughness
decreases
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ConvexPerimeter
Perimeter
Roundness
„ As particle becomes
circular, value
approaches one.
Length
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4( Area)
2
π ( LengthFeMax )
Roundness of metal particles
„ Metal particles are used for powder metallurgy
„ Round particles flow better (e.g., during injection
molding) and provide stronger parts
Low quality nickel alloy powder. Note the small fraction
of very round particles
HORIBA Application Note AN164: Particle Size and Shape Analysis of Metal Powders
© 2011 HORIBA, Ltd. All rights reserved.
Pharmaceutical Globules
„ Spheres from sugar are often used.
„ Shape matters for future process steps
z incorporation or coating of API’s
z Flow through dispensers
HORIBA Application Note AN140: Particle size and Shape analysis of glass beads for pavement markings
© 2011 HORIBA, Ltd. All rights reserved.
Acetaminophen (API)
© 2011 HORIBA, Ltd. All rights reserved.
Sphericity
„ As particle becomes
spherical, value
approaches one.
„ More sensitive to
small scale bumps
that increase
perimeter than
roundness.
© 2011 HORIBA, Ltd. All rights reserved.
4π ( Area)
( Perimeter ) 2
Circularity, Sphericity, Perimeter, Diameter
Circularity = perimeter of circle / perimeter of particle
Sphericity = Circularity2 =
Aparticle
is inside of
particle perimeter
4πA
P2
area of the particle
circle with same
area as particle
perimeter of the
particle
diameter of circle
of same area
Agreen ~ 77 pixel, diameterred = 10 pixel, perimetergreen ~ 38,5 pixel,
circularity ~ 31 / 38,5 = 0.81, sphericity = 4 * π * 77 / (38.5)2 = 0.812 = 0.65
© 2011 HORIBA, Ltd. All rights reserved.
Proppants
„ Hold open cracks in oils wells to allow oil to
flow to well (Hydraulic Fracturing).
„ Sand is one example of a proppant
„ High roundness and sphericity leads to better
permeability.
„ ISO/DIS 13503-2 recommended sphericity
and roundness of 0.6 or greater, 0.7 for high
strength materials.
„ Note that these definitions of sphericity and
roundness are different from, but related to
the one’s used in this talk.
© 2011 HORIBA, Ltd. All rights reserved.
Distributions
„Just like size, many particle samples
have a distribution of shapes.
„Sometimes a distribution of shapes is
desirable. For example, according to
the USGA, sand that is highly uniform in
size and shape tends to be less stable.
Therefore, sand with a variety of grain
sizes and shapes is better for use in
sand traps.
http://www.usga.org/course_care/articles/construction/bunkers/How-to-Select-the-Best-Sand-for-Your-Bunkers/
© 2011 HORIBA, Ltd. All rights reserved.
Measurement Results
Size- & Shape Results
amount
• size + size distribution
- amount by size
• shape
+ shape distribution
- shape by size
- amount by shape
size
shape
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Sorting
Roughness, “too rough” is red
Roundness, not round enough is green
© 2011 HORIBA, Ltd. All rights reserved.
Measurement Results
Particle Shape: Amounts in a Mixture
Q3 [%]
90
AK_22,15g_0,3%_BZ_LB_n Ü_xc_min_001.rdf
IA_22,15g_0,3%_BZ_LB_n
Ü_mit Aerosil_xc_min_001.rdf
A
IA + AK_je
22,15g_0,3%_BZ_LB_n Ü_als Mischung_xc_min_001.rdf
B
A+B
80
B
70
B
A
60
50
40
A
30
20
10
0
0.1
© 2011 HORIBA, Ltd. All rights reserved.
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
b/l
Measurement Results
Particle Shape:
Amounts in a Mixture
Q3 (round particles) = 32.8%
xc min
xFe max
67.2%
© 2011 HORIBA, Ltd. All rights reserved.
The HORIBA PSA300
„ Turnkey System
z More time getting results and less time
engineering
„ Automated
z Faster
z Less operator labor
z Less operator bias
„ Powerful Software Features
z Image Enhancement
z Particle separation
„ Separate Disperser Option
z More flexible sample preparation
© 2011 HORIBA, Ltd. All rights reserved.
Static or Dynamic Image Analysis?
„ Dynamic
z Broad size distributions (since it is easier to obtain
data from a lot of particles)
z Samples that flow easily (since they must be
dropped in front of camera)
z Samples tumble so sometimes you see more
orientations
z Powders, pellets, granules
„ Static
z Samples that are more difficult to disperse (there
are more methods for dispersing the samples)
z Samples that are more delicate
z Pastes, sticky particles, suspensions
© 2011 HORIBA, Ltd. All rights reserved.
Conclusions
„Image Analysis is good for
zSize
zShape
zSupplementing other techniques
„Shape Analysis is the next step beyond
size
zChoice of parameters is very application
dependent.
© 2011 HORIBA, Ltd. All rights reserved.
Questions?
www.horiba.com/us/particle
Jeffrey Bodycomb, Ph.D.
[email protected]
866-562-4698
© 2011 HORIBA, Ltd. All rights reserved.
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