What is a particle? The simplest definition is a minute portion of matter. Within the scope of this document particles do not include subatomic particles such as electrons, protons, neutrons, quarks, etc. Particles measured by the techniques described here include solids (powders), solids in liquids (suspensions), and liquid/liquid emulsions. Not all particles exist as individual entities. They have a habit of sticking together to form various kinds of clusters, or agglomerates. In the field of particle technology, we typically define agglomerates as a loose arrangement of larger structures while aggregates are denser, harder to disperse collectives.
Most particles are not ideal spheres, but irregular in shape. This creates a quandary when defining the size of a particle using a single descriptive value. The diameter of some kind of equivalent sphere is the only available approach to describe particle size using a single number. The International Union of Pure and Applied Chemistry (IUPAC) definition of the equivalent diameter of a non-spherical particle is equal to a diameter of a spherical particle that exhibits identical properties (e.g., aerodynamic, hydrodynamic, optical, electrical) to that of the investigated non-spherical particle. Most particle sizing techniques report results as an equivalent spherical diameter (ESD).
This paper reviews different analytical techniques for particle size analysis, including types of distributions, laboratory versus online systems, and sample result comparisons. It is intended to help those new to particle size analysis understand each technique’s various strengths and weaknesses in order to select the proper technique for their samples.