Hierarchically porous Al2TiO5 ceramics via freeze-gel casting

Abstract

Porous Al2TiO5 ceramics have drawn increasing attention in diverse applications owing to their low thermal expansion coefficient, and good resistance to thermal shock; however, Al2TiO5 ceramics prepared in previous studies still exhibited a relatively high density, which limited their further application in the field of high-temperature thermal insulation. Herein, we reported the successful fabrication of hierarchically porous Al2TiO5 ceramics with a unique three-dimensional skeleton structure formed by overlapped ceramic nanofibers. Results show that the introduction of SiO2 into Al2TiO5 nanofibers could significantly improve their thermal stability and meanwhile reduce their formation temperature. Al2TiO5 nanofibers with 10 mol% SiO2 exhibited a superior microstructure and excellent thermal stability, and were selected as the raw material in the subsequent preparation of corresponding porous ceramics. Porous Al2TiO5 ceramics prepared by the freeze-gel casting exhibited a unique hierarchical pore structure with large pores originating from the sublimation of ice crystal and small pores formed by the overlapped of fibers. This unique microstructure endowed porous ceramics with an ultra-high porosity (97.59–95.59%), ultra-low thermal conductivity (0.0456–0.0754 W m−1 K−1) and excellent thermal stability. Owing to these outstanding characteristics, the resulting porous Al2TiO5 ceramics are expected to be employed as the high-temperature thermal insulation material in a wide spectrum of advanced applications.