Comparative Study on the Effects of Mechanical Treatment by High-Energy Ball Milling on Talc and Kaolinite

A comparative study on the effects of mechanical treatment by high-energy ball milling on talc (2:1 layered silicate) and kaolinite (1:1 layer silicate) was performed. Industrial samples of talc and kaolin were characterized by XRF, thermal analysis (DTA and TG), and XRD methods. The XRD analysis evidenced the destruction of the crystalline structures of both talc and kaolinite and accessory minerals in the samples, showing an increase in the amorphous phases and a progressive change to a more disordered structure. It was found that high-energy ball milling resulted in a reduction of 48% of talc at 4 h of grinding, and the reduction increased up to ~80% at 32 h. The mechanical treatment produced a decrease in initial kaolinite content by 25% after 4 h of grinding and a reduction of ~70% after 32 h. It was deduced by this analysis that the structure of kaolinite is more difficult to destroy by high-energy ball milling than the structure of talc under the same experimental milling conditions. The structural alterations in talc and kaolinite were anisotropic, with crystal degradation along [00l], and there was a progressive loss of long-range order; moreover, the crystal dimensions following the c-axis direction became too small to produce coherent diffraction. A decrease in crystal size (coherent diffraction microdomain) was observed by the mechanical treatment, with an increase in microstrains produced by high-energy ball milling. Thus, the crystal size decreased from 280 to 200 Å in talc (direction perpendicular to 002) and from 250 to 210 Å in kaolinite (direction perpendicular to 001) after 16 h of grinding, with an important reduction in crystal size up to a value of 138 Å but only in the case of kaolinite at 80 h of grinding, with talc completely amorphous to X-rays at the same grinding time. Microstrains followed an inverse evolution compared to the crystal size, with an increase in the values obtained by progressive grinding in both talc and kaolinite. The values of microstrains were found to be of the same order for talc and kaolinite, although they were relatively higher for talc since it is associated with a greater degree of structural alteration than kaolinite. The XRD results showed an inverse correlation between both parameters, with their relative values being higher for talc compared with kaolinite. The present study is of basic interest for further investigations into the effects of high-energy ball milling using talc and kaolin as raw materials with reduced particle size, for instance, in the ceramic and paper industries.