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

ABSTRACT 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.