Composites of phlogopite mica platelets of composition KMg_3AlSi_3O_(10)(F,OH)_2 dispersed in potassium-based potassium geopolymer were fabricated. The platelet additions of up to 25 wt% were achieved which increased the flexure strength and thermal conductivity of pure potassium-based geopolymer. A maximum 3-point flexure strength at room temperature was measured as 11.4 MPa with a standard deviation of 0.34 MPa for 25 wt% mica additions. Heat treatments caused chemical decomposition and water loss at temperatures up to 700 °C and eventual formation of glassy and crystalline leucite at 1000°C. A maximum post-treatment strength of 10.7 MPa with a standard deviation of 0.52 MPa was obtained for the 1000°C heat-treated samples. The thermal conductivity increased from 0.24 ± 0.000 W/mK for pure K-based geopolymer to 0.30 ± 0.008 W/mK, as a function of mica platelet additions up to 10 wt %.
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