Solid-state synthesis and formation mechanism of barium hexaaluminate from mechanically activated Al2O3–BaCO3 powder mixtures

The synthesis and formation mechanism of barium hexaaluminate compound (Ba-β-Al2O3) by solid-state reactions between powdered reactants of alumina (Al2O3) and barium carbonate (BaCO3) have been investigated. The processes for synthesizing Ba-β-Al2O3 phase include mechanically activated milling of Al2O3–BaCO3 powder mixtures and subsequent solid-state reactions at high temperatures. The mechanically activated milling results in a significant decrease in the decomposition temperature of BaCO3, hence promotes its reactions with Al2O3. Almost monophasic Ba-β-Al2O3 can be synthesized by 9–12 h ball milling, followed by heat treatment at 1500 °C for 2 h. The formation of Ba-β-Al2O3 phase includes three stages: (i) decomposition of BaCO3, (ii) formation and growth of spherical BaO·Al2O3 particles, and (iii) reaction between Al2O3 and BaO·Al2O3 to form Ba-β-Al2O3 with an elongated morphology.