Effect of Microsize and Nanosize TiO₂ on Porous Mullite-Alumina Ceramic Prepared by Slip Casting

Sintered porous mullite-alumina ceramics are obtained from the concentrated suspension of powdered raw materials such as kaolin, gamma and alpha Al₂O₃, and amorphous SiO₂, mainly by a solid-state reaction with the presence of a liquid phase. The modification of mullite ceramic is achieved by the use of micro- and nanosize TiO₂ powders. The phase compositions were measured using an X-ray powder diffraction (XRD) Rigaku Ultima+ (Tokyo, Japan) and microstructures of the sintered specimens were analysed using scanning electron microscopy (SEM) Hitachi TM3000-TableTop (Tokyo, Japan). The shrinkage, bulk density, apparent porosity, and water uptake of the specimens was determined after firing using Archimedes' principle. The apparent porosity of the modified mullite ceramic is 52-69 ± 1%, water uptake is 33-40 ± 1%, pore size distributions are 0.05-0.8 μm, 0.8-10 μm and 10-1000 μm, and bulk density are variated from 1.15 ± 0.05 to 1.4 ± 0.05 g/cm³. The microsize TiO₂ and nanosize TiO₂ speed up the mullitisation process and allow the decrease in the quantity used as raw material amorphous SiO₂, which was the purpose of the study. The use of nanosize TiO₂ additive increases the porosity of such a ceramic, decreasing the bulk density and linear thermal expansion.