Novel facile nonaqueous precipitation in-situ synthesis of mullite whisker skeleton porous materials

High strength, lightweight mullite whisker skeleton porous materials were prepared via novel facile nonaqueous precipitation method. The phase transition process of precipitate, microstructures and phase compositions of samples, and effects of aluminum fluoride amount on morphologies and properties of mullite whisker skeleton porous materials were investigated by DTA-TG, FE-SEM, XRD, the acid solubility and compressive strength tests. The growth direction of the whisker was determined. The growth mechanism of mullite whisker and formation mechanism of skeleton porous material were also investigated. The results show that the mullite phase forms at a low temperature of 900 degrees C via nonaqueous precipitation method, due to the formation of Al-O-Si bonds in the precipitate. The formation of mullite whiskers is controlled by gas-solid reaction and the whiskers grow along [001] direction. Well-developed mullite whiskers interlacedly grow into skeleton porous material at 1100 degrees C. The optimum mullite whisker skeleton porous material with the optimized aluminum fluoride amount of 1.3 of theoretical amount exhibits attractive properties of low density (1.21 g cm(-3)), high strength (158.6 MPa), low acid solubility (1.58 wt%), low thermal expansion coefficient (1.6 x 10(-6) degrees C-1) and low thermal conductivity (0.28 W/(m K)). This material has the mean pore size of 542 nm and pore size distribution of 32-865 nm. It shows attractive application prospects in filtering and biomedical applications.