Effect of tio2 on mullite formation in mixture of nigeria sourced kaolinite and calcined alumina

Abstract

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 1600oC 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 1600oC.