Effect of the grinding circumstances on the mechanical activation of fly ash in stirred media mill

The application of the stirred media mill in dry mode came to the front only in recent years, but at the same time several questions arise, such as aggregation, agglomeration, sticking on the liners and the grinding media. During high energy milling, not only the particle size reduces, but among others, in numerous cases the crystal structure and the amorphous state of the material also change due to the mechanical activation taking place. The present paper deals with experiments carried out on the ultrafine fly ash grinding in dry mode at various grinding conditions in a stirred media mill to investigate the mechanochemical effect and the energy efficiency of the mill. During the experiments the particle size distribution, particle shape, specific surface area, amorphity and crystal structure of the products were examined. The product related stress model was used for the evaluation of the effect of milling parameters on the mechanical activation. It was found, based on the experimental results, that there is mechanochemical effect on crystal structure of fly ash in the stirred media mill, as it was revealed by X-ray diffraction and FTIR measurements. The experimental results made it possible to determine the effect of the rotor circumferential speed and so the stress intensity on the mechanical activation of fly ash could be revealed.