Crystallisation of nepheline-based glass frits through fast-firing process

The aim of this research was to study the feasibility of producing sintered nepheline glass-ceramic through a fast firing route. The thermal behaviour of the original glass was analyzed by mean of differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The microstructural analysis of glass-ceramic materials was carried out by field-emission scanning electron microscopy (FE-SEM). The results showed that the studied wastes are able to produce a glass and glass-ceramic materials through a sinter-crystallisation process, 100 μm being the critical glass particle size. Glass-ceramics are composed of residual glassy phase and crystalline phases such as nepheline (NaAlSiO4), augite (Ca, Na)(Mg, Fe, Al)(Si, Al)2O4 and a solid solution belonging to the melilite group (Ca, Na)(Al, Mg, Fe,)(Si, Al)2O7. In a first evaluation, water absorption (0.02%) and bending strength (71 MPa) of glass-ceramic achieved after thermal treatment at 1100 °C/5 min suggest that sintered glass-ceramics can be easily produced from coal fly ash and metallurgical slag wastes by a fast-firing cycle and they are extremely serviceable for outdoor flooring and wall cladding.