Low-temperature fabrication and properties of porous calcium hexaluminate (CA6) ceramics with low thermal conductivity by one-step method

In this study, one-step molten salt method followed by low-temperature sintering is employed for fabricating porous calcium hexaluminate (CA6) ceramics with ideal plate-like structure and low thermal conductivity via the assistance of CaCl2. The porous CA6 ceramic containing 15 wt% CaCl2 sintered at 1400 °C for 3 h exhibits desirable compressive strength (7.14 MPa), low bulk density (1.47 g/cm3), high porosity (61.12%), and low conductivity (0.439 W/(m·K)). The results imply that CaCl2, as a pore-forming agent and an additional source of CaO, provides a large number of liquid phases and resulting in quantities of closed pores. Moreover, the reactions between molten Al2O3 and CaCl2 alter the mass transfer modes of Al2O3 and accelerate its phase transition to α-Al2O3 in addition to contributing to the conversion of CaCl2 to CaO and the subsequent formation of CA6, which results in the entire synthesis of low-temperature CA6 at around 1400 °C. Therefore, there is no need for extra salt washing treatment owing to the consumption and evaporation of CaCl2, which makes this one-step molten salt method much more advantageous in terms of its economical and highly efficient.