Technological properties of glass-ceramic tiles obtained using rice husk ash as silica precursor

This paper reports the results of a study focused on the obtainment of glass-ceramic by using rice husk ash (RHA) as silica precursor. RHA is a by-product generated in biomass plants using rice husk as fuel for kilns or in the rice mills to generate steam for the parboiling process. Worldwide, it is annually produced about 132 Mt of rice husk, which gives rise to a production of 33 Mt/year of RHA. Glass-ceramic tiles were produced by a sinter-crystallization process using a glassy frit formulated in the MgO–Al2O3-SiO2 composition system. The realized glass-ceramics were studied according to ISO rules for sintering and technological properties (water absorption, apparent density, bending strength, Young's modulus, deep abrasion, Mohs hardness). To complete the investigation crystalline phase formation and microstructural characterization of the glass-ceramic materials was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Finally, chemical durability tests on parent glass and derived glass-ceramics were performed. The results obtained showed that it is possible to use RHA to produce glass-ceramic tiles by a sinter-crystallization process, obtaining nepheline (Na2O*Al2O3*SiO2) as main crystalline phase and forsterite (2MgO*SiO2) at 900 °C. Regarding technological features, the sintered materials showed bending strength values and Mohs hardness higher with respect to commercial glass-ceramics like NeopariesR. Other properties as water absorption (0.5%) allowed to classify these materials into the Group BIa characteristic of high sintered ceramic tiles according to European Standard rule.