Microstructure and integrity of leucite ceramic derived from potassium-based geopolymer precursor

In this paper, leucite ceramics with different shapes and fine integrity were directly developed from geopolymer precursors by the optimized heat treatment procedures. Phase compositions and microstructure, coupled with the mechanical properties, were systematically investigated. The effect of heating rates on the integrity of ceramics was also discussed. After high-temperature treatment at 800 °C for 120 min, the geopolymer was converted into a leucite ceramic. The relative density of the sample treated at 1000 °C for 120 min was 93% and the size of leucite grain was approximately 1–4 μm. TEM results showed that the leucite grain was composed of lamellar and needle-shaped twins, which resulted from the displacive phase transformation as it went from cubic to tetragonal symmetry when it was cooled down. Samples with plate and bullet shapes maintained their fine integrity by the optimization of the heating procedures. Meanwhile, the flexural strength, Young's modulus, fracture toughness and Vickers hardness of the leucite ceramic that resulted was 70.0 MPa, 65.0 GPa, 1.3 MPa m1/2 and 7.39 GPa, respectively.