Fabrication of Structural Leucite Glass-Ceramics from Potassium-Based Geopolymer Precursors

Leucite glass-ceramics were fabricated by cold isostatically pressing K2O center dot Al2O3 center dot 4SiO(2)center dot 11H(2)O geopolymer powders into pellets followed by firing at 950 degrees-1200 degrees C, every 50 degrees C in air. Leucite formation was observed in specimens heat treated to >= 1000 degrees 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 center dot m1/2, 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 degrees 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.