Titania was progressively added in the range 3–9 wt% into a triaxial porcelain body consisting of clay, quartz and feldspar. The composed bodies were heated at five different temperatures in the range 1200–1400°C and their fired properties as well as phases evolved were studied. The results revealed that beyond 1300°C, formation of more liquid phases caused bloating in samples which led to generation of pores. This effect is more pronounced in TiO₂ containing samples. In the present system, 1300°C appeared to be the optimum temperature at which porosity was almost negligible and strength was maximum (45 MPa), particularly in presence of TiO₂. From the results of XRD studies, it was revealed that quartz content primarily decreased with increase in TiO₂ content due to excess glass formation and its subsequent dissolution. Mullite content increased with increase in TiO₂ content. No significant effect was observed beyond 6 wt% addition. Microstructure primarily showed the presence of quartz grain and cluster of smaller sized primary mullite crystals in both the samples without and with TiO₂. Very few secondary mullite crystals were also observed. SEM picture of sample containing 9 wt% TiO₂ showed some grain boundary crack due to cooling stress generated in the glassy phase. The drastic reduction of residual strength after 8 cycles of heating at 800°C and cooling particularly in TiO₂ containing samples suggests controlled heat treatment of the vitrified samples necessary to promote secondary crystallization process for the enhancement of strength. Attempts have also been made to correlate the constitutional parameters with the properties.

Titania doped vitrified triaxial porcelain samples were subjected to controlled heat treatment at different temperatures of 600, 800 and 1000°C with a specific heating schedule. The results revealed that flexural strength of 800°C heat treated sample was significantly enhanced to 60 MPa from its original value of 40 MPa. XRD pattern revealed the formation of mullite in the system both before and after heat treatment and the differences in their growth was ascertained through SEM analysis. The present heat treatment process may be useful to produce high strength porcelain body from a common triaxial system.

Clay and reactive alumina were used to prepare mullite ceramic by wet mixing, followed by the solid-state sintering method. The influence of lanthanum oxide (La$_2$O$_3$) additive for phase formation, microstructural evolution, densification, flexural strength, hardness and thermal shock resistance was studied. The calculated amount of the raw materials, i.e., kaolinite, reactive alumina and different wt% La$_2$O$_3$ additive according to the stoichiometric composition of mullite (3Al$_2$O$_3$.2SiO$_2$) were wet mixed, dried and uniaxially pressed, followed by sintering at different temperatures for 2 h. The La$_2$O$_3$ substitution (3 wt%) positively impacts mullitization by reducing phase formation temperature. A quantity of 3 wt% La$_2$O$_3$ added batch sintered at 1600°C shows strength and bulk density of 196.5 MPa and 3.041 g cm$^{-3}$, respectively. Columnar grains with interlocked morphology were formed by adding a La$_2$O$_3$ additive that improves the bending strength. Retention of strength after 9 cycles of thermal shock is measured and found satisfactory. Higher quantity La$_2$O$_3$ addition showed a deleterious effect on bending strength and hardness of the samples.