Effect of TiO2 on mullite formation in mixture of Nigeria sourced kaolinite and calcined alumina

In this study, the effect of TiO2 when added to a mixture of Nigerian sourced of kaolin and calcined alumina powder (50:50) was investigated. The influence of Ti4+ ion on the physico-mechanical property (apparent porosity, bulk density and modulus of rupture), phase and microstructural evolution was studied at sintering temperature of 1600?C when mullitisation has been maximized based on previous reports. The sintered samples showed considerably high porosity of about 16 %, a slight reduction of about 5 % in porosity was observed on TiO2 addition. There was no appreciable change in the bulk density due to TiO2 doping, but the modulus of rupture (MOR) reduced appreciably from 43 MPa to 36 MPa on TiO2 doping. As shown by the XRD, mullite was seen as the major phase with negligible cristobalite phase for the undoped sample. The TiO2 doped sample displayed mullite as major and corundum as minor phases. There appeared more mullite phases in the doped sample than the undoped sample indicating a higher percentage of mullite formation. The microstructural study shows the presence of acicular mullite with round edges and good aspect ratio. The presence of inter-granular and intra-granular pores in TiO2 doped samples might have contributed to the reduction in strength observed at 1600?C.

Investigation of the sintering kinetic and development of ceramic masses for obtaining large-format porcelain stoneware in the conditions of high-speed firing

The paper considers the resource and energy saving reserves in the production of large-format stoneware slabs. The possibility of replacing high-quality feldspars with materials of technogenic origin, such as the extraction and processing waste of various feldspar-bearing rocks of domestic deposits has been investigated. The possibility of sintering process intensification has been investigated, as a condition for the use of high-speed firing modes in the stoneware production. As a result of the carried out studies, the kinetic features of ceramic masses sintering with alkaline syenites, granites and pegmatite enrichment wastes as fluxing component were determined. The formation conditions of densely sintered materials with a complex of high operational properties have been determined. The expediency of replacing Turkish feldspars with waste products of alkaline syenites has been established, while the level of physical, mechanical and operational properties of stoneware slabs meets the requirements of international standards. It is shown that, the use of complex flux, including feldspar-bearing rocks waste and dolomite, provides a significant decrease in the firing temperature of products (up to 1150 °C) while maintaining a high level of properties of stoneware slabs of class BІa. The obtained data indicate the possibility of optimizing the heat treatment parameters from the view point of energy saving with the further use of alternative fluxes in the large-format stoneware production. On the example of using the alkaline syenites wastes, the optimal ratios of the clay and fluxing components of ceramic masses have been established to obtain products with a complex of high performance characteristics when burning white clays of different chemical and mineral composition, which is a necessary condition for using a wide range of decorating techniques stoneware slabs. The structural-phase features of materials obtained under the conditions of high-speed firing are established: the formation of finely dispersed acicular mullite, which plays the role of a reinforcing component, as well as high structural homogeneity and maximum compaction, as evidenced by a few individual small pores presence. The combination of excellent technical qualities and large dimensions opens up new possibilities for the use of stoneware slabs as structural elements (countertops, ventilated facades, insulating panels for the installation of electrical systems, etc.).