TPDSci PSD by sedimentation Intro

PSD measurement by sedimentation: Introduction

Sedimentation is a well established method of determining the particle size and PSD (for example, Jonasz M and Fournier 2007, pp. 368-376). In a gravity-driven sedimentation chamber, particles are either introduced at the top of a sedimentation channel (tube) containing clear liquid (case 1) or dispersed evenly throughout the channel (case 2) and are allowed to settle (for example, Syvitsky et al 1991a). In each case the attenuation of light by the dispersion (or another relevant property of the dispersion) is measured at a fixed distance from the tube top as a function of time. The sedimentation process can be accelerated, and the lower particle size limit decreased by subjecting the dispersion to an acceleration many times greater than that of gravity, as that in a disk centrifuge (for example, Middleberg et al 1990). This latter method is referred to as the photosedimentation.

The sedimentation method, as described, relies on the assumption that all particles have the same density. As the settling velocity of a particle is a function of the particle size, particles with various sizes either pass through the measurement zone (case 1) or settle out of it (case 2) at various times. This enables one to retrieve the PSD from the time-evolution of the attenuation of light by the dispersion at the measurement zone. The use of the settling velocity as the particle size indicator implies that the particle size measured by this method is the equivalent hydrodynamic diameter (EHD) of the particle.

The sedimentation method applies to dispersions in which the effect of the Brownian motion is negligible (see Sedimentation vs. Brownian motion).

CITATION:
Jonasz M. 2006. PSD measurement by sedimentation: Introduction (www.tpdsci.com/Tpc/PsdSdmIntro.php). In: Top. Part. Disp. Sci. (www.tpdsci.com).

HISTORY:
Published: 13-Jan-2006
Modified: 26-Nov-2006
Peer-reviewed: PENDING

Topics in Particle and Dispersion Science