Porous Alumina/Mullite Layered Composites with Unidirectional Pore Channels and Improved Compressive Strength

Three-layer porous alumina-mullite composites with a symmetric gradient porosity are prepared using a controlled freeze/gel-casting method. In this work, tertiary-butyl alcohol (TBA) and coal fly ash with an appropriate addition of Al₂O₃ were used as the freezing vehicle and the starting material, respectively. When sintered at 1300-1500℃, unidirectional macro-pore channels aligned regularly along the growth direction of solid TBA were developed. Simultaneously, the pore channels were surrounded by less porous structured walls. A high degree of solid loading resulted in low porosity and a small pore size, leading to higher compressive strength. The sintered porous layered composite exhibited improved compressive strength with a slight decrease in its porosity. After sintering at 1500℃, the layered composite consisting of outer layers with a 50 wt% solid loading showed the highest compressive strength(90.8 ± 3.7MPa) with porosity of approximately 26.4%.