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Evolution of pyrophyllite particle sizes during dry grinding

P. UHLÍK^1,*, V. UCHA¹, D. D. EBERL², L’. PUKELOVÁ³ and M. APLOVIOVÁ¹

¹ Faculty of Sciences, Comenius University, Mlynská Dolina G, 842 15 Bratislava, Slovakia, ² US Geological Survey, Marine Street, Boulder, CO, USA, and ³ Geological Institute, Slovak Academy of Sciences, Dúbravská 9, 842 12 Bratislava, Slovakia

^* E-mail: uhlik{at}fns.uniba.sk

(Received 8 April 1999; revised 30 June 1999)

The Bertaut-Warren-Averbach (BWA) technique and high-resolution transmission electron microscopy (HRTEM) were used to characterize the products of dry-ground pyrophyllite. Mean crystallite thickness and crystallite thickness distributions were measured for each sample using the BWA technique. Mean crystallite thickness decreases during the treatment with respect to grinding time and energy applied per unit mass. The BWA data were checked by HRTEM measurements and good fits were obtained for samples having small mean particle thicknesses. Samples with thicker particles could not be measured properly by HRTEM because the number of particles counted from images is statistically insufficient. The shape of the crystallite and the particle-size distribution were used to determine the mechanism of pyrophyllite particle degradation. Particles initially having a lognormal size distribution are first delaminated randomly, then some are delaminated preferentially, thereby producing polymodal thickness distributions. Finally all particles undergo delamination yielding a lognormal thickness distribution.

KEYWORDS: Bertaut-Warren-Averbach technique, grinding, pyrophyllite crystallite, HRTEM

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