Infrared transparent mullite ceramics fabricated by solid-state reactive sintering

Abstract Infrared transparent mullite ceramics were fabricated by solid-state reactive sintering under vacuum without pressure. High purity α-alumina and amorphous silica (molar ratio, 63: 37) powders were used as raw materials. The densification process and mullitization process of the mixed powders were investigated and compared with the sintering of mullite powder. As the sintering temperature increased to 1400 °C, mullite formed and silica transformed into cristobalite. Cristobalite disappeared at 1600 °C and α-alumina did at 1650 °C. However, α-alumina precipitated when the temperature increased to 1750 °C. For the sintering of mullite powder, shrinkage happened at 1400 °C. While, shrinkage almost finished for the reactive sintering of alumina and silica. When reactive sintered at 1780 °C, the transmittance of the mullite ceramics was the highest, which was 65% at 4.1 μm. The method used in this work is promising for the preparation of large and complex shaped transparent mullite ceramics.