Particle characterization

1
Particle characterization

• Chapter 6

2
Why determinate particle size

• List three things that you know will be affected
  by particle size

3
My three things

• Delivery of particles to the lungs
• Solubility of active pharmaceutical compounds
• Bulk density

4
What do you want to characterize

• Particle
• Size
• Morphology
• Material properties
• Porosity
• Density
• Hardness/elasticity(later)
• Surface properties
• Chemical composition
• Surface energy
• Roughness

• Powder
• Particle distribution
• Flowability/cohesion
• Specific surface
• Density
• Porosity
• Air content
• Water content (later)

5
Size and Morphology Describe these two particle
collections
6
Size and Morphology Different descriptive terms
for particles

• Particle form
• spherical, ellipsoid, granular, blocky, flaky,
  platy,prismodal, rodlike, acicular, needle
  shaped, fibrous irregular,dendrites, irregular,
  agglomerates
• But also particle surface
• Smooth, spotty, rough, porous, with cracks,
  hairy

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Size and Morphology Measurement of particle size

• Reduce to known geometry
• Volume
• Cubes
• Spheres
• Ellipsoids
• Area
• Circles
• Squares
• Ellipses
• Lengths
• Characteristic lengths
• Feret and Martin diameters
• Relate to the geometry
• Fit into the geometry
• Have equal Volume or Area
• Have equal properties

A Projected a rea PPerimeter dequivalent
diameter Ssurface area Vvolume
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Size and Morphology Descriptors based on
diameters of circles

• dcircDiameter of circumscribed minimum circle
• dinscDiameter of inscribes maximum circle
• deqDiameter of the circle having same area as
  projection area of particle
• Shape descriptorCircularity
• deq/dcirc

9
Size and Morphology More descriptors according
to the same principles
Namn Definition Formula
Volume diameter Diameter of a sphere having the same volume as the particle
Surface diameter Diameter of a sphere having the same surface as the particle
Surface volume diameter Diameter of a sphere having the same surface to volume ratio as the particle
Projected area diameter Diameter of the circle having the same area as the projection area of particle
Perimeter diameter Diameter of the circle having the same perimeter as the projection peramiter of particle
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Size and Morphology Feret and Martin diameter
Df0

• The Feret diameter the distance between two
  tangents to the contour of the particle in a well
  defined orientation.
• The Martin diameter, is the length of a line that
  divide the area of the particle into two equal
  halves.
• Normally measured
• Mean the mean over several orientations
• Ylargest
• Xsmallest
• Elongation Y/X

Dm0
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Size and Morphology Unrolled diameter

• The mean chord length through the center of
  gravity of the particle

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Size and Morphology Diameter Defined from equal
properties

• Drag diameter
• Diameter of a sphere having the same resistance
  to motion as the particle in a fluid of the same
  viscosity and the same speed
• Free-falling diameter
• Diameter of a sphere having the same density and
  the same free-falling speed as the particle in a
  fluid of the same density and viscosity
• Stoke diameter
• The free falling diameter of a particle in the
  laminar flow region
• Aerodynamic diameter
• the diameter of a sphere of unit density (1g/cc)
  that has the same gravitational settling velocity
  as the particle in question.

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Size and Morphology Stoke diameter

• For small particles lt0.5?m Brownian motions
  counteract gravitational forces and the system
  will be stable
• For larger particles
• Density matching will hinder sedimentation

msolventg
Brownian motion
a
mpartg
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Size and Morphology Diameter Defined from equal
properties contin..

• Equivalent light-scattering diameter
• Diameter of the sphere giving the same intensity
  of light scattering as that of a particle,
  obtained by the light-scattering method
• Sieve diameter
• The diameter of the smallest grid in a sieve
  that the particle will passe through

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Size and MorphologyFrom descriptors

• Elongation L/B or dferet(max)/dferet (min)
• Circularity for example dins/dcirc
• Sphericity (Wandells)

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Size and Morphology Form descriptors

• Form factors f/k will describe the form
• Space Filling Factor The ratio between the area
  of a circumscribed rectangle or circumscribed
  circle of the image and that of the particle eg
  A/LB eller 4A/pr2

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Material propertiesDensity

• True particle density The density of the
  material
• Apparent particle density Density of the
  particle when inner porosity is included
• Effective or aerodynamic particle density
  Density if outer porosity is included. Related to
  the density that a air or gas stream will measure.

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Surface properties Particle surface

• Properties
• Roughness of the surface
• Composition
• Surface energy
• Influences
• Stability
• Total area
• Particle size reduction
• Adsorption of other substances to the surface
• Aggregation
• Release of adsorbed material

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Surface properties To evaluate surfaces
properties

• ESCA, XPS - Composition
• FTIR - Composition
• AFM- Surface morphology and surface energy
• Raman microscopy- composition
• Electron microscopy -Surface morphology

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Surface properties To evaluate surface energy -
Contact angles

• Gives information on how easily a liquid wets a
  surface.
• Low contact angle with water for hydrophilic
  surfaces.
• Contact angle hysteresis
• Chemically heterogeneous surface.
• Surface roughness.
• Surface porosity
• Surface changes when wetted.

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Assignments particlesTask

• Test and compare two different techniques for
  size determinations (half a day)
• Microscopy
• Light scattering
• Answer the questions in the assignment
  description on a seminar (Tue 28 Apr 13.15)
• As usuell hand in a short technical note

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Assignments particlesPractical issues

• Do the assignment in groups of three
• Use our sample or your own
• Microscopy use the microscope to take picture but
  do the major part of the analyses afterwards
  Image J is a free program

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Size distribution Particle size distribution

• Why is the mean value not enough to describe
  particle size distributions
• How can we describe the distribution
• Based on what properties
• Based on what type of statistic distribution

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Size distribution Type of distributions

• Different type of diameters
• Different type of distribution
• Number (0)
• Length (1)
• Area (2)
• Volume (3)
• Weight (w) V?

• How will these differ from one another?
• How do you calculate the mean particle size
• Can you transfer mean particle size between the
  different distributions?

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Size distributionAverage particle size
Number mean length diameter d(1,0) 2
Number mean surface diameter d(2,0) 2,16
Number mean volume diameter d(3,0) 2,29
Weighted mean length diameter d(3,0)
Length surface mean diameter d(2,1) 2,33
Length volume mean diameter d(3,1) 2,45
Surface Volume mean diameter d(3,2) 2,57
weight moment mean diameter d(4,3) 2,72
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Size distributionDifferent distributions
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Size distribution Type of statistic distribution

• Normal distribution
• Log Normal
• RosinRammler (Weibull) Distribution

28
Size distribution Special properties of log
distributions

• If the number is log distributed so is the
  length, surface, and volume
• With the same geometric mean deviation
• Hatch-Choate relationships will transfer one type
  of mean diameter into another

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Size distribution Description of particle size
distribution

• Mean diameter
• Standard mean,
• Geometric mean
• variability
• Standard deviation
• Geometric standard deviation
• Skewness

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PowderSpecific surface

• Surface per weight
• Factors that increase surface area
• Decrease in particle size
• Increase in surface roughness
• Inner porosity (if available)
• Method dependent parameter
• Permeatry
• Gas adsorption
• Gas diffusion
• Porosimetery

• Importance
• Dissolution
• Chemical reactions
• Adsorption of other molecules
• Flow though particle beds

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PowderDensity, air content and porosity

• Density (?b) weight of powder/Volume of powder
• Air content air in pores(entrapped air) and air
  in between particles (void air)
• Porosity
• In particle
• Between particles

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PowderFlow properties and powder density

• Angle of repose
• Bulk density
• Tapping density
• Carrs index
• Hausner ration

Flow character Angle Carrs index
Very good lt20 5-15
Good 20-30 12-16
Ok 18-21
Poor 30-34 25-35
Very poor 33-38
Extremely poor gt40 gt40