ESTIMATION OF THE AVERAGE ASPECT RATIO OF LAMELLAE-SHAPED PARTICLES BY LASER DIFFRACTOMETRY

Reinforcing properties for polymers and elastomers, rheological properties of high density aqueous slurries, hidding power, lubricating properties of platey particles strongly depend on their size distribution and shape factor or aspect ratio (A.R.).

Determinations of A.R. of fine particles by conventional methods are time-consuming and require sophisticated equipment. A method based upon later light diffractometry has been developed to meet control requirements in industry, the average A.R. can be determined within 5 to 10 minutes, depending upon the number of measurements made using a commercial laser granulometer.

The method relies on:

a cylindrical model (disc) of platey particles.

determinations of the projected area of particles in dilute suspensions of controlled solids concentrations.

calibration of the instrument, using isodiametric particles

simple material balance to derive the average thickness h of the platey particles from projected area measurements and volume of the solid.

A.R. is defined as d50(S)/h. where d50(S) is the mean projected area diameter and h the average thickness attributed to all particles occurring in the sample.