Fine particles play essential roles in determining the characteristics of both natural and manmade materials and have considerable influence on processes such as dissolution, adsorption and reaction rate. In most cases, these effects are a function of either the size, shape, surface area or porosity of the individual particles or of an agglomeration of particles. These particle-related characteristics must be controlled in order to optimize the desired effects, and efficient control requires measurement. There are multiple techniques for determining the same particle dimension and each has its advantages and disadvantages.
Selecting a technique that is inappropriate for the application can have a deep impact on the quality of the measurement you obtain.

Particle Analysis Techniques

Industrial particles fall into the size range (µm) shown below.

A size measurement method must match the sizes ranges below.

Image Analysis

The phrase image analysis includes any technology which involves the processing of captured images. For the purposes of particle characterization, the major division is between static image analysis and dynamic image analysis. The distinction is whether particles are presented.

In Static Image Analysis the particles generally are located on a glass slide.

In Dynamic Image Analysis, the particles are flowing on front of a detector or digital camera.

Comparing Image Analysis for three different samples to Other Techniques.

There are three different particles: Glass Spheres, Garnet and Glass Wollastonite that have been analyzed with different techniques and the results are shown for comparison.

Glass Spheres results

One would expect similar results here for each technique, since the glass beads are nearly spherical, and the various methods relate size to an equivalent sphere. The median (D50) results are very similar for all the particle size methods.

Garnet results

Garnet is not spherical; rather, it is more cube-shaped. With cube-shaped samples, the diagonal distance between opposite corners is longer than the diameter of an equivalent volume sphere by about 30%. Therefore, the results are larger with the flowing techniques (light scattering and image analysis) than with the instruments which are sensitive to the equivalent spherical diameter.

Wollastonite results

The same flow and shape effects that resulted in slightly different garnet particle sizes are more pronounced with the rod-shaped Wollastonite. The light-scattering technique sees the largest particle dimension. The electrical sensing zone and sedimentation techniques report a particle diameter equivalent to a spherical measurement. Light scattering has a thicker flow path than the image analyzer and therefore some particles can be oriented with the smaller size exposed to the detection system.