Changes in the structure of talc by continuous jet milling in relation to imposed specific kinetic energy

Abstract

Ultra fine talc is used in many industries such as paper, paints, polymers, cosmetics and pharmaceutical. Emerging demand with stringent specification from these industries has marked jet mill as one of the essential grinding mill to produce ultra fine talc. Ultra fine grinding testwork of talc was carried out in opposed fluidized bed jet mill by varying the feed rate, classifier rotational speed and grinding pressure at three levels. In this jet mill, grinding and classification took place simultaneously. The ground products were characterized in terms of particle size distribution and mechanochemical effect via X-ray diffraction. The ground product exhibited poly-modal distribution and the minimum size obtained was 4.28 µm at 4 kg/h, 13000 rpm and 4 bar. Besides size reduction in micron range, mechanochemical effect was exhibited by the product ground in jet mill as jet mill is classified as high-energy mill. Reduction in peak intensity and peak base broadening was observed which indicates fine grinding process in jet mill induced mechanochemical effect. Furthermore preferential distortion of (00l) planes was observed as well. The degree of crystallinity of ground sample, which ranged from 26.5% to 85.3% reduces as the specific kinetic energy increase and its reduction gradient varies according to the classifier rotational speed. The crystallite size and lattice strain of talc ranged from 147.69 nm to 353.72 nm and 0.08 to 0.2 respectively.