Low sintering shrinkage and high strength of porous mullite–zirconia ceramics: Effect of AlF3 and ZrSi2 contents

Abstract Low‐shrinkage porous mullite–zirconia ceramics were prepared using Al and ZrSi 2 as raw materials and AlF 3 as the whisker catalyst through foam‐gelcasting and freeze‐drying methods. The oxidation of Al and ZrSi 2 combined with the Kirkendall effect and volume expansion was employed to reduce the sintering shrinkage, while the mullitization was promoted by the reaction between AlF 3 and extra ZrSi 2 , and ZrO 2 were generated to enhance the compressive strength as the reinforcing phase. The effect of AlF 3 and ZrSi 2 content on the microstructure and properties of porous mullite‐zirconia were explored. These ceramics exhibited high porosity (73.75%–85.02%) and compressive strength (2.98–17.71 MPa), low shrinkage (0.47%–10.89%) and thermal conductivity (0.228–0.462 W/(m·K)). In particular, the porous mullite–zirconia ceramics with great compressive strength (4.01 MPa) companied with near‐zero shrinkage (0.47%) at the AlF 3 content of 15 wt% and extra ZrSi 2 content of 20 wt% by introducing the reinforcing phase (ZrO 2 ). Additionally, the temperature difference around 950°C of the porous ceramics during the heating test proved the exceptional application on thermal insulation.