Mullitization behavior and microstructural development of B2O3-Al2O3-SiO2 mixtures activated by high-energy ball milling

This paper reports on phase formation and microstructural development of mullite, derived from B2O3-Al2O3-SiO2 mixtures activated with different milling methods. It is found that the addition of B2O3 has a positive effect on mullite phase formation from the mixture of Al2O3-SiO2, which can be qualitatively attributed to the fact that B2O3 brought out higher nucleation density and enhanced reaction kinetics. Anisotropic grain growth of mullite was not observed in the unmilled mixture since mullite phase formation occurred after densification. Dense and interlocking microstructures of mullite ceramics were produced from the mixture activated with stainless steel milling media, whereas mullite whiskers were formed in the samples milled with tungsten carbide media. The high-energy ball milling refined the precursors and thus reduced the mullitization temperature. As a result, anisotropic microstructures and mullite whiskers could be derived from the milled mixtures. This way to produce anisotropic microstructures of mullite ceramics is very simple and requires temperatures much lower than those reported in the literature. This method is believed to be useful to fabricate reinforced mullite or mullite-related materials via in-situ anisotropic grain growth. (C) 2009 Elsevier Masson SAS. All rights reserved.