Introduction
After reading this chapter you will have a basic idea of the operating procedures of
the Mastersizer and in particular:
.
Know the basic operating principles of the Mastersizer.
.
Know the simple steps involved in making a measurement and analysing
the data. More detail will be given in later chapters.
What does the Mastersizer do?
Scientists have for centuries tried to predict the way particles scatter and absorb
light. There are many theories and models that the modern particle analyst can
use.
One of the simplest theories used is the Fraunhofer model. This model can
predict the scattering pattern that is created when a solid, opaque disc of a known
size is passed through a laser beam.
This model is fine for a lot of particles but it does not describe the scattering
exactly. Very few particles are disc shaped and a lot of particles are transparent.
The Mie theory was developed to predict the way light is scattered by spherical
particles and deals with the way light passes through, or is adsorbed by, the
particle. This theory is more accurate but it does assume you know some specific
information about your particle, such as its refractive index and its absorption.
The key fact about these theories is that if you know the size of the particle and
other details about its structure, you can accurately predict the way it will scatter
light. Each size of particle will have its own characteristic scattering pattern, like a
fingerprint that is unlike any other size of particle.
So how does the Mastersizer measure the size of particles? The Mastersizer works
backwards from the above theories by using the Mastersizers’ optical unit to
capture the actual scattering pattern from a field of particles. Then using the
theories above it can predict the size of particles that created that pattern.
CHAPTER 3
GETTING STARTED
Page 3.1
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