Nirendra Krishna Mitra

Effect of titania on fired characteristics of triaxial porcelain

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.

Effect of TiO2 on the interaction of dehydroxylated kaolinite with Al(OH)3 gel in relation to mullitisation

Mullite being a material of prime importance in ceramics has drawn attention for a long time. Precursor powder for mullite was prepared in the active state by the aqueous phase interaction of dehydroxylated kaolinite and deposited aluminium hydroxide gel from Al(NO3)3 solution. Magnitude of sintering as well as the sintered properties of the compacted mass was found to be influenced by the doping agent, TiO2.

Effect of Cr2O3 on the sintering of aluminosilicate precursor leading to mullite formation

Aluminosilicate precursor material for mullite formation was synthesized using wet interaction of the ingredients like aluminum nitrate and silicic acid sol in the aqueous route. The gel was characterized by chemical analysis, measurement of surface area, bulk density and X-ray analysis. Sintering of the gel powder was carried out at different elevated temperatures from 1300°C to 1450°C in presence of Cr2O3 as a doping agent. The different physico-mechanical properties of the sintered compacts, such as, volume shrinkage, bulk density, porosity etc. were measured. X-ray diffraction and SEM analysis of the compacts were further carried out to evaluate the degree of sintering of the powder in presence of Cr2O3. It was observed that Cr2O3 plays a positive role in the formation of mullite at elevated temperature from the aluminosilicate gel precursor.