Fabrication of structural leucite glass-ceramics from potassium-based geopolymer precursors

Leucite glass-ceramics were fabricated by cold isostatically pressing K₂O·Al₂O₃·4SiO ₂·11H₂O geopolymer powders into pellets followed by firing at 950°-1200°C, every 50°C in air. Leucite formation was observed in specimens heat treated to ≥1000°C. The relative density, Vickers hardness, fracture toughness, and biaxial flexural strength of sintered samples ranged approximately 96%-98%, 767-865 kg/mm², 0.94-2.36 MPa·m^1/2, and 90-140 MPa, respectively. The toughness and biaxial flexure strength increased with the firing temperature, while the density and hardness were relatively constant. Scanning electron microscopic and transmission electron microscopic analysis revealed that the sintered geopolymer formed leucite crystals and a compositionally variable glassy phase. Samples heated to 1200°C attained the highest biaxial flexure strength and toughness. This higher strength is believed to arise from an optimum in density, leucite content, and crystal size distribution.