The effect of titanium slag on the properties of glass-ceramic composites from South African coal fly ash

Abstract

In this study, the impact of titanomagnetite slag on the structure of glass-ceramic composites was investigated. The slag was added as a source of titania which promotes nucleation within the parent glass matrix and magnesium oxide which facilitates crystallisation. A mixture of fly ash and varying quantities of waste beverage glass and titanomagnetite slag were melted. The melts were then annealed at lower temperatures to reduce the internal stress and, subsequently, cooled to room temperature to produce parent glasses. The mass of fly ash was held constant at 60%, while the mass of the waste beverage glass and titanomagnetite slag was varied between 10-30% and 0-30% respectively. Afterwards, the parent glasses were converted to glass-ceramic composites through a controlled double-staged thermal treatment. Characterisation of these composites showed that an increase in titanomagnetite slag resulted in many crystal phases forming within the glass-ceramic matrix and an increased porosity. The desired diopside phase was not detected in the composites same as when pure magnesium oxide was added instead of the titanomagnetite slag. The compressive strengths, the bulk densities and melting temperatures of the glass-ceramic composites were found to be lower as compared to glass-ceramic composites produced from a mixture containing pure magnesium oxide. However, they were highly resistant to attack by nitric acid and sodium hydroxide.