Influence of Grain Size and Firing Temperature on the Structure of Porous Magnesia Ceramic

Abstract

Changes in the structure and physical properties of porous magnesia ceramic containing TiO₂-Al₂O₃ matrix with TiO₂/Al₂O₃ molar ratio 0.96 and 15wt% content were studied at different sizes and firing temperatures for controlling the pore shape. The shape of pore was complicated depending on the grain size and firing temperature, and pores were found to have a fractal nature. While the fractal dimension increased with increasing firing temperature for small grains, it decreased with increasing firing temperature for large grains. The fractal dimension of each MgO grain size tends to converge at a lower firing temperature which is close to the temperature at which the MgAl₂O₄-Mg₂ TiO₄ solid solution is formed. Specimens with small grains were found to shrink on firing, but the expansion was observed for large grained specimens. These phenomena were explained by the densification and molar volume of MgAl₂O₄-Mg₂TiO₄ solid solution and CaTiO₃ formed. From the above facts, it was possible to controll the pore shape by grain size and firing temperature.