Effect of alkaline-earth oxides on phase formation and morphology development of mullite ceramics

The effect of alkaline-earth oxides, including MgO, CaO, SrO and BaO, on the phase formation and morphology development of mullite (3Al2O3·2SiO2) ceramics from oxide mixtures activated by a high-energy ball milling process, were investigated. Different alkaline-earth oxides demonstrated different influences on the mullitization behavior and morphology/microstructure development of the mullite ceramics. Mullitization temperature increased as the additives were from MgO to BaO. Well developed mullite whiskers were formed in the MgO doped group, while grains with normal shapes were observed in the cases of CaO, SrO and BaO. The dependence of both mullite formation temperature and morphology development on the kinds of alkaline-earth oxides were explained in terms of the mullitization mechanism of dissolution–precipitation.