Mechanical activation of barium aluminate formation from BaCO3–Al2O3 mixtures

The effect of high-energy ball milling and subsequent annealing on a mixture of Al2O3 and BaCO3 has been investigated. DTA results show that the initiatory decomposition temperature of BaCO3 decreases with the increase of ball milling time duration. X-ray diffraction (XRD) measurement indicates that the nanocrystalline powder mixture is produced and no BaAl2O4 is formed during a high-energy ball milling process after milling for 30 h. Significant crystallization of BaAl2O4 from the nanocrystalline powder mixture milled for 5 h, 15 h and 30 h is observed after annealing at 900 °C, while a trace of BaCO3 exists at this temperature. Single phase BaAl2O4 can be obtained for the sample milled for 5 h at 1000 °C, which is at least 200 °C lower than that used in the traditional solid-state method, while the secondary crystalline phases Ba5Al2O8 and BaCO3 exist for the physical mixture at 1000 °C. No significant grain is observed when the milled powders were annealed at 1000 °C with different milling time and the average size of the grain is about 0.3–0.5 μm.