Determination of the particle size of fine powders, with particular reference to kaolins

Abstract

AbstractThe sedimentation curves for suspension of kaolins from Central Europe, Italian bentonites and clays have been obtained by using a hydrostatic balance provided with a normal plunger. Investigations undertaken to establish the accuracy of the method and the theoretical calculation of the sedimentation curves are briefly described. The possibility of applying Stokes' law to the mass settling of kaolins is also discussed. The authors wish to emphasize (a) the possibility of determining the average diameter of powder particles by means of the tangent to the curve at zero time, and (b) the possibility of deducing from experimental sedimentation curves both the curves relating to size distribution (the number of particles as a function of equivalent diameter) and the cumulative curves (the percentage by weight of particles having dimensions smaller than one determined equivalent diameter).When carrying out sedimentation measurements, particularly with kaolins, it is possible to obtain regular curves only when conditions are such as to avoid flocculation. This result is achieved by adding suitable electrolytes in quantities which determine the smallest sedimentation volume.The average equivalent diameters of the powders examined were deduced from such sedimentation curves.Statistical measurements of dimensions made by direct microscopic observations have been carried out on two kaolins from Central Europe, resulting in average values which agree very closely with those calculated from the sedimentation curves.Cumulative curves of the usual type have been obtained from the densimetric curves of sedimentation.