A novel aqueous gel-casting for fabricating Al2O3-bonded fibrous mullite ceramics

Abstract

Al2O3-bonded fibrous mullite ceramics with high porosity have been prepared by a novel aqueous gel-casting method using the ρ-Al2O3 and mullite fibers as raw materials and the deionized water as hydration agent. A bird nest structure with three-dimensional reticular skeleton was established by the fibers to ensure having a certain mechanical strength. The effects of the amount of mullite fibers on the properties of porous ceramic including phase composition, microstructure, sintering behavior, mechanical and thermal properties were investigated. The results showed that the fabricated Al2O3-bonded fibrous mullite ceramic had high porosity of 66.9%–78.6%, low density of 0.70 g/cm3 to 1.17 g/cm3, low thermal conductivity of 0.236 W/mK to 0.479 W/mK, and relatively high compressive strength of 0.80 MPa–2.78 MPa. With increasing the amounts of mullite fiber, the apparent porosity increased, the bulk density and thermal conductivity decreased. When the ratio of mullite fibers was 67%, the porous ceramic had the maximum porosity of 78.6%, the minimum thermal conductivity of 0.236 W/mK, and the relatively high compressive strength of 1.12 MPa, which could fully meet the application requirements of the thermal insulation materials.