Influence of particle size on the crystallization kinetics of glasses produced from waste materials

The crystallization behavior and kinetics of glasses produced from coal fly ashes, red mud and silica fume were investigated by using differential thermal analysis, X-ray diffraction and scanning electron microscopy techniques. The kinetic parameters of the glass-crystallization transformation were estimated under non-isothermal conditions applying three different equations, namely, Kissinger, Matusuta-Sakka and Ozawa. Non-isothermal differential thermal analysis curves were obtained using both coarse and fine glass samples. The crystallization activation energies of coarse glasses are in the range of 233–439 kJ/mol while the activation energies of fine glasses change in the range of 369–450 kJ/mol. Avrami exponent, n, values of coarse glasses indicated the three-dimensional bulk crystallization. This result is in well agreement with the cross-sectional scanning electron microscopy investigations. The values of the n obtained experimentally are in the range of 1.24–1.36 for fine glasses which show the one-dimensional surface crystallization. The crystallized phase of the glass-ceramic samples produced from waste glasses by applying the controlled heat treatment process was identified as diopside by X-ray diffraction analysis.

Research Highlights
► n, values of coarse glasses indicated the three-dimensional bulk crystallization, while the n values of fine glasses showed the one-dimensional surface crystallization.
► The activation energy values for crystallization increased with the decrease in particle size of the waste glasses.
► XRD results revealed that the glass-ceramic samples produced from the different mixed wastes which had similar chemical compositions have the same crystalline phase determined as the diopside phase.
► The cross-sectional SEM investigations on the bulk glass-ceramic samples indicated that this result is in well agreement with those determined by Ozawa equation.