Anisotropic grain growth of mullite

In this report, mullite ceramics with anisotropic grains were attained from a mixture containing aluminum oxide (Al2O3) and silica (SiO2) from high-energy ball milling. The effects of sintering temperature (1000oC, 1100oC, 1200oC, 1300oC, 1400oC and 1500oC) and time duration (1, 2, 3 and 4 h), on phase formation, grain growth and densification of the mullite ceramics were studied. Characterization techniques used in this project include X-ray diffraction (XRD) and scanning electron microscopy (SEM). Densities of the samples were calculated by using the measured dimension and mass. Phase formation of mullite started at the lowest sintering temperature of 1000oC, but anisotropic grain growth was not started and thus mullite whiskers were not present in the samples. However, anisotropic grain growth was observed as temperature increased to 1200oC, with dimensions of the grains growing proportionally thereafter. At a temperature of 1500oC, single phases of mullite were completely formed and anisotropic grains were more evident. Densification of mullite was low initially at low temperatures, which was attributed to the loose packing of the whiskers within the matrix. There is room to adjust the density/porosity of the materials by controlling the sintering parameters. Such mullite ceramics could be used as porous ceramic materials that could be fabricated without the use of pore forming agent (polymer spheres). The finding from this report also brings up new opportunity to make textured mullite ceramics by using the whiskers as templates.Bachelor of Engineering (Materials Engineering