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

Abstract

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.