Effect of MgO addition on crystallization, microstructure and properties of glass-ceramics prepared from solid wastes

Abstract

Glass-ceramics can be used as architectural materials. Fly ash from municipal solid waste, screen glass and ceramic polishing slag were used to prepare glass-ceramics by a synergistic sinter-crystallization method. The effect of MgO addition on crystallization behavior and environmental compatibility of glass-ceramics was investigated. Crystallization kinetics analysis showed that surface crystallization dominated the overall crystallization process in the MgO content range from 1.1% to 7.5%. The glass transition temperature and the crystallization peak temperature of the glass-ceramics decreased gradually with the increasing content of MgO. Along with, the main phase of the glass-ceramic was changed from tabular spars to pyroxene and boltonite. The crystal morphology gradually developed from rod-like and sheet-like to sphere-like, while the grain development became refined and sample density gradually increased. When the MgO content was 7.5%, the performance of glass-ceramics reached its optimum, with the volume density of 2.77 g/cm3, water absorption of 0.03%, the bending strength of 86.5 MPa, and micro-hardness of 7.2 GPa. All the performances were superior comparing to the natural marble, granite, and commercial glass-ceramics. The as-prepared glass-ceramics were submitted to leaching assays with toxicity characteristic leaching procedure (TCLP) leaching method at pH of 2.9 and 4.9, which demonstrated that the heavy metals could be effectively immobilized in as-prepared glass-ceramics. The final building products converted from solid wastes were non-toxic to the environment, which had good environmental compatibility.