AGGLOMERATION AND SOLUTION OF PARTICLES DURING SEDIMENTATION ANALYSIS

A basic requirement of particle size analysis through sedimentation is the perfect dispersion of the particles in suspension. The dispersion must be perfect and stable. To ensure this, for a number of solids DIN 66111 specifies sedimentation liquids and suitable dispersing agents and defines an upper limit for the concentration of the solids in suspension. Some instruments require higher solids concentrations than are recommended in DIN 66111. However, there is no simple test to prove the stability of a dispersion with sedimenting particles. An effective method for testing the stability of a dispersion is to make a number of simultaneous sedimentation analyses, measuring the concentration of the particles at different distances from the surface of the liquid. If the dispersion remains perfect, identical particle concentrations have to be measured, when the measuring time is normalized to one distance from the surface (e.g. t1′ = t(h3/h1), t2′ = t(h3/h2) …). From the particle concentration, distance from the surface and time, the particle size distribution can be calculated. If the results of the lower (and hence later) measurement show a shift to the larger diameters, agglomeration has occurred. If the sensing technique is light extinction, then the effect is particularly pronounced. A photosedimentometer with three light beams at distances from the surface of 1.5, 15 and 150 mm was used to demonstrate the effect of agglomeration on particle size distribution and to optimize sedimentation liquids and dispersing agents. An attempt was made to determine the kinetics of agglomeration from the increase in transmission of a light beam through a suspension. Copyright © 1990 Verlag GmbH & Co. KGaA, Weinheim