Texas A

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Texas AM University KingsvilleDepartment of
Environmental Engineering

• EVEN 6356
• Lecture Topic
• PARTICLE SIZE ANALYSIS
• By
• PRAJAY GOR
• March 29, 2007

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Outline

• Introduction
• Importance of Particle Size Analysis
• Types of Measurement
• Particle Size Instruments
• Particle Size Analysis Methods
• - Sieving
• - Gravitational Sedimentation
• - Microscopy
• - Laser Light Diffraction
• Sources of Error and Variances
• References

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Introduction

• Particle
• - a discrete element of material
  regardless of its size.
• Particle size
• - the sizes of a particle, determined
  by the smallest dimension, for
• instance a diameter. It is usually
  expressed in micron measurement.
• - the controlling lineal dimension of
  an individual particle as
• determined by analysis with sieves
  or other suitable means.
• Particle Size Analysis or Particle Size
  Distribution
• - classification of powder material as
  determined by various testing
• methods define the particle sizes
  and quantities in a given sample.
• - a description of the size and
  frequency of particles in a population.

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Importance of Particle Size Analysis (PSA)

• Heywood wrote- However, it must be realized
  that particle size analysis is not an objective
  in itself but is a means to an end, the end being
  the correlation of powder properties with some
  process of manufacture, usage or preparation.
• PSA is a prerequisite for most production and
  processing operations.
• PSD has a significant effect on the mechanical
  strength, density, electrical and thermal
  properties of the finished products.
• Particle size and PSD affects key colloid
  properties such as rheology, film gloss, surface
  area and packing density.
• High rejection rate of product occurs if PSA is
  not carried out accurately.

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Types of Measurement
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Particle Size Instruments
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Particle Size Analysis Methods
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Flowchart for General PSA Procedure
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PSA SIEVEING TECHNIQUE

• A test sieve is a measuring device designed to
  retain particles larger than a designated size
  while allowing smaller particles to pass through
  the device.

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Sieving Technique

• Size range 125 mm to 20 micrometer
• Specimen type Dry, free flowing powders. Some
  designed for analysis of slurries.
• Operation mode Mostly offline in batch mode.
  Some automated systems for quality control.
• Strengths
• - low capitol cost
• - low level of technical expertise
• - minimal sample preparation
• Limitations
• - long analysis time
• - mechanical motion affects
  repeatability and reproducibility of results
• - error due to improper maintenance,
  improper material transfer
• - uncertain when particles have high
  aspect ratio (eg. Needle shaped
• particles

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Reporting of size data using graphical
representation such as (a) Histogram, (b)
Frequency curve, (c) Cumulative Arithmetic Curve
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Gravitational Sedimentation Technique

• Instruments based on principle of gravitational
  sedimentation measures the velocity with which
  particle settle due to gravity, against buoyancy
  of the fluid and other drag forces acting against
  settling of particles.
• Based on Strokes law.
• Particles reach terminal velocity rapidly and in
  very short travel distance.
• X-ray beam gravitational sedimentation using
  x-ray or photo gravitational sedimentation using
  light beam can be used as a probe to determine
  concentration of particle at a given depth in
  fluid column..
• Attenuation in the intensity of the beam due to
  either absorption (x-ray) or scattering (light)
  of probe signal is used to measure particle
  concentration.
• The intensity of beam after attenuation is
  compared with intensity of beam in the absence of
  any particles, measured on a baseline signal.
• Thus, knowing the particle density and by
  determining the concentration of particle at
  various depths, the settling velocity is
  determined and particle diameter corresponding to
  velocity calculated.

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Flowchart for X-ray Gravitational Sedimentation
Technique
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Gravitational Sedimentation Technique

• Size range 0.1 micron to 300 micron (0.001
  micron to 1000 micron are possible with certain
  instruments).
• Specimen type Powders dispersed in suspension.
  Suspensions can be aqueous or non-aqueous.
• Strengths
• - simple specimen preparation
• - rapid analysis (except below certain
  size limits)
• - inexpensive instrumentation
• - no skilled labor required
• Limitations
• - cannot be used for powder batch with
  different particle densities
• - analysis time increases with increase
  in fraction of fine particles.
• - accuracy is affected by physical
  factors such as solid loading,
• particle-particle interaction,
  Brownian motion.
• - reduced sensitivity, accuracy and
  resolution of materials with density
• close to that of dispersion medium.

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PSA Microscopy based techniques

• Involves direct observation of the particles and
  the consequent determination of size is based on
  defined measure of diameter.
• Calculated sizes are expressed as the diameter of
  a sphere that has the same projected area as the
  projected image of the particle.
• Instruments based on microscopy technique have
  conventionally included optical light microscope,
  scanning electron microscope (SEM) and
  transmission electron microscope (TEM).
• Helps to characterize particle size, particle
  shape, size distribution and morphology.
• Software packages are available for particle size
  and size distribution.

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Flowchart for Microscopy based PSA
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Microscopy based technique

• Optical light microscope
• - affordable
• - easier to operate
• - sample easily prepared and in short
  time
• - limited magnification and resolution
• Scanning electron microscope
• - size range 0.1 micron to 1000 micron
• - high magnification and resolution
• - can view particles of varying sizes
  in the same field of focus
• - greater time required for sample
  preparation
• Transmission electron microscope
• - size range 0.01 micron to 10 micron
• - high resolution
• - can view particles of varying sizes
  in the same field of focus
• - greatest time required for sample
  preparation

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PSA by Laser Light Diffraction Technique

• Laser light diffraction technique is a non
  imaging technique using light beam as a probe.
• Assumptions
• - particles scattering the light are
  spherical in nature
• - no multiple scattering
• - scattering pattern at the detector is
  the sum of the individual
• scattering pattern given by each
  particle interacting with the incident
• beam in the sample volume
• Instruments are designed with capabilities for
  applying various optical models for the
  deconvolution of the scattered pattern and size
  determination.
• - Fraunhofer model for size analysis
  (2 micron to 8000 micron)
• - Mie optical model ( 0.1 micron)

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Schematic of components in a typical Laser
Diffraction Instrument
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Flowchart for PSA by Light Diffraction Technique
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PSA by Laser Diffraction Technique

• Size range 0.04 micron to 8000 micron
• Specimen type Powders dispersed in suspensions.
  Some can be used for dry powders specimens
• Strengths
• - rapid analysis
• - relatively inexpensive
• - simple specimen preparation
• - can be used on-line as well off-line
• - used for dry powders and powders in
  suspension
• Limitations
• - highly dependent on instrument design
  (eg. laser sources of different
• wavelengths, differing number and
  position of detectors)
• - requires knowledge of optical
  properties of specimen
• - cannot differentiate between dispersed
  particles and agglomerate
• - error occurs if particle size differs
  from spherical configuration

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Sources of Error and Variances

• Sampling and specimen related errors
• - non-representative sampling
• - inadequately prepared powders
• - contamination
• - specimen degradation during storage
• Instrument and analysis related errors
• - improper calibration of instrument
  and software
• - non-maintenance
• - defective or damaged tubings
• Errors due to human and other factors
• - operator fatigue
• - incorrect statistical analysis
• - lack of understanding

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References

• Bernhardt, C., Particle Size Analysis Problems
  and Possibilities in the Fine and Ultrafine
  Range, Journal of Material Synthesis and
  Processing, Volume 8, Nos. 3 / 4, 2000.
• Jillavenkatesha,A., Dapkunan, S.J., Lum, L.H.,
  Particle Size Characterization, National
  Institute of Standards and Technology, January
  2001.
• Scarlett, B. 25 Years of Particle Size
  Conferences.
• European Commission Institute of Health and
  Consumer Protection. Guidance document on the
  determination of particle size distribution,
  fibre length and diameter distribution of
  chemical substances.