Preparation of porous mullite ceramics composed entirely of overlapping and interlocking mullite whiskers through whisker in-situ growth

A novel porous mullite ceramic with overlapping and interlocking mullite whiskers was prepared using in-situ whisker growth technology. Without the use of any pore-foaming agents, the formation of a porous structure was facilitated by the atomic rearrangement of Al2O3 and SiO2 catalyzed with MoO3. The effects of the molar ratio of Al2O3 to SiO2, MoO3 content, sintering time, and sintering temperature on the structure and properties of (xAl2O3·ySiO2)m(MoO3)n-T-t (T = sintering temperature, and t = sintering duration) ceramics were comprehensively studied. The molar ratio of Al2O3 to SiO2 had a more significant effect on the morphology of the whiskers, while the other three conditions generally promote whisker growth. Under conditions of x : y = 3 : 1.8, m : n = 9 : 1, T = 1300 °C, and t = 3 h, (3Al2O3·1.8SiO2)9(MoO3)1-1300 °C-3 h ceramics exhibited a satisfactory compressive strength of 4.81 MPa at a density of 0.76 g/cm3. Microstructural analysis revealed that a multi-level reinforcement structure was obtained by the interlaced distribution of tiny and large whiskers, significantly increasing the crack deflection area and enhancing the crack deflection resistance when resisting external forces. After 100 thermal shock cycles between room temperature and 1300 °C, the compressive strength retention rate was 77.13%. In addition, the multi-scale whisker-overlapping structure also has a high specific surface area (1.83 m2/g), high porosity (74.18%), and small pore size (7.44 μm). The thermal conductivity was as low as 0.260 W/(m·K), and the ceramic maintained a rear-side temperature below 200 °C when subjected to a 1300 °C butane flame. In addition, the regulatory mechanism between parameters, structure, and properties was analyzed in detail, providing data support for research on porous materials.