Sinter-crystallization of spodumene LAS glass-ceramic tiles processed by single-firing

For the manufacturing of glass-ceramic products, a monolithic glass is prepared using the same technologies for the conventional glass production, followed by a thermal-treatment of nucleation and crystal growth. An alternative process could be the production of glass-ceramic materials by pressing of glass powders and densification by sintering. In this way, the same equipment used in a traditional ceramic tile plant could be used to produce components with complex geometry. In this work, the single-firing process was used to obtain LAS glass-ceramic (Li2O.Al2O3.SiO2) tiles. The aim of the work was to determine the effect of particle size, pressing and sintering temperature on the bending strength and thermal expansion coefficient of the glass-ceramic tiles. The raw materials were melted in alumina crucibles (1480 °C, 80 min) and the obtained glass was quenched in water and annealed (600 °C). The glass was milled for 1 and 2 h (ball mill), resulting in two particle sizes, 9.1 μm (1 h) and 22 μm (2 h). The powders were granulated and pressed at 35 and 45 MPa, resulting in four processing conditions. In sequence, the compacts were dried (150 °C, 24 h) and sintered at 1175 and 1185 °C (10 °C/min heating rate). The microstructure of the glass-ceramic tiles was determined by SEM and XRD techniques. The bending strength was determined by the 3-point method and the thermal expansion coefficient (CTE) was determined by dilatometry. As a result, LAS glass-ceramics tiles were obtained, showing high modulus of flexural strength (70–80 MPa) and very low thermal expansion coefficients (1.2–1.4 × 10−6 °C−1). Surface crystallization was achieved and the main phase was β-spodumene. Sintering was simultaneous to crystallization, in a typical one-step process.