Effect of the different additives on the fabrication of porous kaolin-based mullite ceramics

Porous mullite ceramics were prepared from kaolin and Al2O3 with different sintering additives TiO2, MgO and MoO3. The sintering aids have a significant influence on the grain morphology and densification process by varying the composition and viscosity of liquid phase during firing. The addition of TiO2 retarded the mullite transformation. The introduction of MgO promoted the secondary mullite transformation and the formation of needle-like mullite grains. Compared with MgO, the samples with MoO3 have lower secondary mullitization temperature. The lower secondary mullitization temperature was beneficial for the secondary mullite to grow anisotropically and then to hinder shrinkage during the sintering process. Thereby, the samples with MoO3 showed a network skeleton structure which consists of acicular mullite grains and exhibited a highly open porosity of 67%. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.