Lightweight Insulating Porous Calcium Silicate Ceramics Fabricated Using High-Aspect-Ratio Whiskers

Porous calcium silicate (CaSiO 3 ) ceramics, composed mainly of CaSiO 3 whiskers, are widely used as high-temperature thermal insulation materials due to their high porosity and stability. However, CaSiO 3 whiskers prepared by the dynamic hydrothermal method have defects of low aspect ratio and poor uniformity. To solve these problems, high-aspect-ratio and uniformly distributed CaSiO 3 whiskers were successfully prepared by a two-step “coprecipitation-hydrothermal” method using CaCl 2 and CaO as composite calcium sources and Na 2 SiO 3 as the silicon source. Then porous CaSiO 3 ceramics (TS-CS) were fabricated using these whiskers as the starting materials via gel-casting, and their properties were compared with those prepared by the direct-hydrothermal method (DH-CS). Results show that the addition of CaO regulates the phase transformation process of CaSiO 3 , enabling the powders to form long whiskers with a high aspect ratio. In addition, the TS-CS ceramics have better performance. Results show that the sample sintered at 900°C exhibited a high porosity (90%), low density (0.26 g·cm −3 ), and low thermal conductivity (0.067 W·m −1 ·K −1 ). This work provides a new synthetic route for high-aspect-ratio CaSiO 3 whiskers, which is beneficial to improving the properties of porous CaSiO 3 ceramics.