Microstructure and Residual Stress Effect on the Flexural Strength of Porcelain Tiles Formulated from Locally Available Materials in Uganda

Quartz is an inexpensive raw material used in the production of porcelain tiles. The presence of quartz prevents pyroplastic deformation during sintering. However, the use of quartz particle size exceeding 32 µm has a deleterious effect on the flexural strength of porcelain tiles. Therefore, the aim of this study was to investigate the effect of microstructure and residual stress on the flexural strength of porcelain tiles formulated with different quartz particle sizes, within the range of 45 to 200 µm. The samples made of kaolin, feldspar and quartz were mixed in the ratio of 5:3:2 respectively, and die pressed at 40 MPa. Afterwards, the green body was sintered at 1300 0C for 2 hours at a rate of 60 0C/min. The microstructure of the sintered body was characterized by using a scanning electron microscope (SEM) to examine the nature and size of the pores. In addition, the residual stress was evaluated based on X-ray diffraction (XRD) method and corroborated with SEM. The flexural strength was determined using three points loading method. The samples formulated with quartz particle size of 45 µm exhibited smooth granules, and isolated pores within the range of 3-8 µm. But, those with 200 µm particles size exhibited rough granules, and interconnected pores between 10-34 µm. Initially, there was an increase in the residual stress, but above 90 µm particle size, it decreased due to evolution of cracks. Also, an increase in quartz particle size resulted in a decline in flexural strength from to MPa. These results show that increasing quartz particle size affected the pore morphology and the residual stresses. Therefore, fine quartz particle milling should be taken into account for further improvement of flexural strength.