Effect of mechanical activation on the structural, morphological and textural properties of synthetic high-charge micas

Abstract

Dry grinding is an effective method for mechanically activating clay minerals to enhance their efficiency in various material applications. This is achieved by increasing the number of exposed active sites and the overall surface area through particle size reduction. Nevertheless, this method frequently results in a reduction of crystallinity or alterations in the structure of the clay material. In this context, trioctahedral clays with a high aluminum content exhibit greater structural resistance to degradation. Thus, this work aimed to employ dry grinding as an effective top-down nano-sintering method to obtain nano-clays from the high-charge mica family. High-charge micas are a group of trioctahedral synthetic micas with aluminum in the tetrahedral layer, widely studied because of their interesting adsorption properties. The novelty of this work laid in demonstrating that dry grinding can effectively reduce the particle size of high-charge micas to the nanoscale while preserving their structural integrity, representing a significant advancement in the controlled mechanical activation of trioctahedral clays without inducing amorphization. To reduce the risk of amorphization, gentle milling conditions were applied using a planetary ball mill. After 15 min of grinding at 500 rpm, a substantial reduction in particle size from microns to the nanoscale was obtained, while preserving the long and short-range order of the material. Moreover, despite prolonged grinding, an increase in external surface area was still evident, while the characteristic structural properties of micas remained intact. Montmorillonite, a natural clay mineral, was used as a reference for comparing the structural and textural properties under equivalent grinding conditions.