Methods of Measuring Particle Size Distribution

Abstract

The methods most widely used at present to determine the dispersive composition of dust particles and powders are sieve analyses, sedimentometry and air separation. These methods are applied to determine the distribution of particles according to mass in samples of a medium. Sieve analyses can be used to determine the dispersity of particles having a radius of greater than 20μm. The method of sedimentometry has been applied in many devices for determining the fractional composition of dusts and powders having radii over 0.5 μm. Many devices rely on aerial separation of dusts of varying dispersive compositions consisting of particles having radii of over 0.5 μm. In some devices of that type samples are taken in the main pipeline. Methods of microscopy are also widely used to determine particle distribution according to size. These methods require preliminary sampling of the dust or powder. The minimum radius of the particles which may be investigated by optical microscopy is 0.1 μm, and by electronic microscopy is 3 × 10⁻⁴ μm. In Kouzov (1971) it is pointed out that all methods based on sampling from gaseous media have a number of shortcomings in common. Sampling may be attended by the formation of aggregates. Before the particle dispersity in the selected section is measured, the particles are once more dispersed in the liquid or gaseous medium and this gives a false picture of the initial dispersive composition of, say, dust. Thus, the results of such measurement are, strictly speaking, conditional.