Synthesis of porous ceramic with well-developed mullite whiskers in system of Al2O3-Kaolin-MoO3

Abstract

Porous ceramics have the advantages of low density, low thermal conductivity, and excellent mechanical properties. One of the scalable methods for manufacturing porous ceramics is the replica method, which provides the advantage of high porosity and the critical disadvantage of low mechanical strength. To overcome this shortcoming, mullite (3Al2O3·2SiO2) whiskers, which have excellent thermal stability and high mechanical strength, were introduced in porous ceramic structure. The mullite whiskers were prepared using Al2O3, kaolin, frit, and MoO3 composition. The addition of MoO3 lowered the mullitization temperature, and the mullite whiskers could be grown at 1100–1400 °C. The morphologies and crystal structures of the mullite whiskers with various the annealing temperatures and MoO3 contents were investigated in detail. The mullite whiskers, which contained 20 wt% MoO3 and was annealed at 1300 °C, showed the highest aspect ratio of 137 with the average length of 46.6 μm and average thickness of 0.34 μm. The compressive strength and porosity of the porous ceramic sample with these mullite whiskers were 0.97 MPa and 87.5%, which were also the highest values.

Keywords

• Mullite whiskers
• MoO3
• Aspect ratio
• Porous ceramic
• Replica method