Vitrification of fly ash from thermal power stations

Samples of fly ash from Spanish thermal power plants were vitrified after mixing with other inorganic wastes such as dolomite slag and glass cullet. The relative viscosity and crystallisation behaviour of the glasses obtained were investigated by hot stage microscopy (HSM) and differential thermal analysis, from which reheating schedules were chosen for recrystallisation. X-ray diffraction analysis (XRD) showed that diopside (augite) and/or wollastonite could be crystallised from these glasses, giving rise to dendritic and/or acicular microstructures which were observed and analysed by scanning electron microscopy (SEM/EDX). It was shown that the glass ceramics so obtained had improved mechanical properties compared with the untreated glasses, with Vickers microhardness (H-v) = 5-6.9 GPa, elasticity modulus (E) = 59-101 GPa and toughness (K-1C) = 1.7-1.8 MPa m(1/2) maximum ranges from glass ceramics products showing better properties.