Porous Mullite Ceramics for Advanced Sensors

Abstract

Porous mullite ceramics were fabricated by activated reaction sintering a mixture of rice husk ash and technical alumina as precursors for SiO₂ and Al₂O₃, respectively. MgO was used as a catalyst. The mixture was attrition milled to particles sizes ranging from 10 to 30 nm. Green compacts were prepared by uniaxial pressing at 50 MPa. Two types of porous mullite ceramics were fabricated. The first one was prepared by sintering the green bodies at 1,300°C for 3 h. An apparent porosity of 20% was achieved, with pore sizes ranging from 100 to 500 nm. Mechanical properties such as E-modulus and bending strength were 80 ± 2 GPa and 130 ± 7 MPa, respectively. The second one was fabricated at 1,500°C for 3 h by using powdered active coal as pore creator. It possessed an apparent porosity of 26 ± 1%, the pore sizes ranged from 5 to 50 μm. Anisotropic grain growth occurred, resulting in needle like mullite structures. The E-modulus and bending strength were 63 ± 3 GPa and 49 ± 2 MPa, respectively.