PARTICLE TECHNOLOGY (PTCT101)
Lecture 1
INTRODUCTION
What is particle technology?
Why is it important?
Particle Size Analysis?
WHAT IS PARTICLE TECHNOLOGY?
The science and technology related to the handling and processing of
particles.
Often described as powder technology, particle science and powder science.
Particles are referred to as bulk solids, particulate solids and granular solids.
Particle technology includes the study of emulsions, liquid drops, bubbles and
solid particles.
This course focuses on solid particles.
WHY IS IT IMPORTANT?
Solids in chemical industries are most commonly in the form of
particles.
Solids are generally more difficult to handle than liquids or gases.
In process industries solids appear in various forms, hard and
abrasive, tough and rubbery, soft and fragile, dusty and cohesive,
free flowing or sticky.
WHY IS IT IMPORTANT?
Particulate materials, powders or bulk solids are used widely in all areas
of the process industries:
Pharmaceuticals
Biotechnology
Water treatment
Chemical mineral processing
Plastics
Cosmetics
Chemical
Knowledge of their properties, handling, storage, transportation,
separation and processing is important from a chemical engineering
point of view.
WHY IS IT IMPORTANT?
Particulate systems that are heavily influenced by particle size
and shape:
The flow of granular materials
The sintering behavior of metallurgical powders
The combustion efficiency of powdered coal
rapid evolution and growth of applications in nanosized particulate
materials, signaling that the increasing importance of particle
characterization is set to continue
PARTICLE SIZE ANALYSIS
What is the particle diameter of my powder? The answer is not that
simple…
PARTICLE SIZE ANALYSIS
What is the particle diameter of my powder? The answer is not that simple…
In powder handling and processing, bulk properties of the powder are
determined by knowing the particle size and distribution.
It is important to measure particle properties:
Better control of the quality of the product (cement, cosmetic powder…)
Better understanding of products/ingredients
Designing of equipment for various operations (separation, crushing…)
PARTICLE SIZE ANALYSIS
The simplest shape of a particle is the sphere in that, because of its
symmetry, any question of orientation does not have to be considered,
since the particle looks exactly the same from whatever direction it is
viewed and behaves in the same manner in a fluid, irrespective of its
orientation.
The size of a particle of irregular shape is defined in terms of the size
of an equivalent sphere although the particle is represented by a
sphere of different size according to the property selected.
PARTICLE SIZE ANALYSIS
Some of the important sizes of equivalent spheres are:
a) The sphere of the same volume as the particle.
(b) The sphere of the same surface area as the particle.
(c) The sphere of the same surface area per unit volume as the particle.
(d) The sphere of the same area as the particle when projected on to a
plane perpendicular to its direction of motion.
PARTICLE SIZE ANALYSIS
(e) The sphere of the same projected area as the particle, as viewed
from above, when lying in its position of maximum stability such as on a
microscope slide.
(f) The sphere which will just pass through the same size of square
aperture as the particle, such as on a screen.
(g) The sphere with the same settling velocity as the particle in a
specified fluid.
PARTICLE SIZE ANALYSIS
Non-spherical particles can be assigned a number of different diameters depending on which parameter is
used in the measurement process
PARTICLE SIZE ANALYSIS
x denotes the diameter of the particle
TYPICAL MEASURES OF SIZE OR LENGTH
SCALE FOR IRREGULARLY SHAPED PARTICLES
TYPICAL MEASURES OF SIZE OR LENGTH
SCALE FOR IRREGULARLY SHAPED PARTICLES
TYPICAL MEASURES OF SIZE OR LENGTH
SCALE FOR IRREGULARLY SHAPED PARTICLES
SIZE DISTRIBUTION
Particle size in a bulk sample does not have
a single value
There is a distribution of specific properties
i.e. size/shape
Particle size distribution is cumulative or
frequency-derived
SIZE DISTRIBUTION
Cumulative
The cumulative distribution, N(x), is the number of particles less
than size x.
Frequency
The frequency distribution, n(x), is defined such that n(x)dx is the
number of particles between sizes x and x+dx
Clearly, N(x) and n(x) are related. From their definitions:
SIZE DISTRIBUTION
From the definition of the frequency size distribution, it follows that the total
area under the n (x) curve must be NT , the total number of particles:
MEASUREMENT OF PARTICLE SIZE:
SIEVING
Dry sieving using woven wire sieves is appropriate for particle size
greater than 45 mm. The length of the particle does not hinder it
passage through the sieve aperture.
The efficiency of screening is defined as the ratio of the mass of
material which passes the screen to that which is capable of
passing.
MEASUREMENT OF PARTICLE SIZE:
SEDIMENTATION
Rep <0.3. Motion of the particle
obeys Stoke’s law.
The suspension is sufficiently dilute
(No hindered settling).
Particles are assumed to
accelerate rapidly to their
terminal free fall velocity, time for
acceleration is negligible.
MEASUREMENT OF PARTICLE SIZE:
SEDIMENTATION
v is the terminal velocity of the particle,
g is the gravitational constant,
d is the particle diameter,
ρ p is the particle density,
ρ is the liquid density and
η is the liquid viscosity.
One of the key implications of Stokes’ law is that the larger particles settle at
a faster rate, which is proportional to the square of the diameter ( v ∝ d 2).
MEASUREMENT OF PARTICLE SIZE:
ELECTROZONE SENSING
As particle flow through the
orifice,
a voltage pulse is recorded.
The amplitude of the pulse
can be related to the
volume of particle the
orifice.
Particle range:
0.3-1000 mm.
NANOPARTICLES
A nanoparticle is a small particle that ranges between 1 to 100
nanometres in size. Undetectable by the human eye, nanoparticles
can exhibit significantly different physical and chemical properties
to their larger material counterparts.
NANOPARTICLES: MEASUREMENT
Dynamic light scattering
Disc centrifugation
Nanoparticle tracking analysis
Tunable Resistive Pulse Sensing
Atomic force microscopy
Electron microscopy
NANOPARTICLES: MEASUREMENT
Electron microscopy
Dynamic light scattering
NANOPARTICLES: MEASUREMENT
Disc Centrifugation
Nanoparticle tracking analysis
