Particle analysis 2 Flashcards
What does coulter counter measure?
The NUMBER of particles in a given band
What does sieving and sedimentation
the MASS of material in a given size
Median
the size that splits the distribution into two hands
measures of dispersion - MONODISPERSE meaning
If the particles in a sample are all of the same size
measures of dispersion - POLY DISPERSE meaning
If a range of particle sizes exists
Measured using GSD
Model distributions what are the two types
normal distribution
lognormal distribution
When do we use normal distributions
when an item is subject to random variation
Particle-size analysis methods can be divided into different categories based on different criteria:
Size range of analysis
Wet or dry methods
Manual or automatic methods
Speed of analysis
What are different methods of analysis
Sieving, microscopy, coulter counter: electrical sensing zone
sieving - how does it work
you stack the sieves in order of ascending aperture size and placing the powder on the top and agitate it and the powder will classify into fractions
a closed pan (called the receiver) goes into the bottom of the stack and collects the fines, then a lid on the top to prevent the loss of powder
Agitation may be manual or mechanical.
The results are expressed in the form of a cumulative undersize percentage distribution.
What does sieving measure?
The sieve equivalent diameter (ds) is defined as the size of a sphere that will just pass through the mesh of a particular sieve
When to use sieving (SUITABILITY)
Separated fraction required for further study.
Material must have good flowability (coarse powder).
The powder is composed of materials with a range of different densities (which would cause difficulties for sedimentation techniques), different refractive indices (problems for light scattering) or is water-soluble or conductive (problems for Coulter counter).
Material is relatively robust (not brittle).
Material must be handled dry.
Sieving is best avoided when…
Much fine powder is present (or very small particle size)
Particles are fragile, which may break during sieving.
The particles are in the form of elongated needles.
The material adheres to the sieve or form clumps.
The powder easily acquires an electrostatic charge
Sieving errors
gauges which reject or pass particles as they are presented at the aperture.
The size distribution given by a sieving operation depends also on the following variables:
duration of sieving
variation of sieve aperture
wear
Microscopy - what is it regarding particle analysis
Individual particles are measures
It is important that the particles selected are representative of the bulk.
The diameter assigned to each particle is a true measure of particle size.
The sample preparation depends on the skill of the operator.
Electrical sensing zone: the coulter counter
what does it measure
the equivalent diameter (volume diameter (dv)
the size range is 0.1 - 1000 (UM)
