EFFECTS OF PROCESSING CONDITIONS ON THE CHARACTERISTICS OF NANO-CRYSTALLINE BARIUM HEXAFERRITE PREPARED BY MECHANICAL ALLOYING METHOD

In this research, the effect of milling time and annealing temperature on a heat activated synthesis of barium hexaferrite from mechanically activated mixture of hematite and barium acetate was investigated. The properties of samples were examined by XRD, DTA/TGA, SEM and VSM methods. The initial mixture with Fe/Ba molar ratio of 11 was milled for 24–48 h and then annealed at 800–1100°C. The XRD results showed the reflections of hematite as a major phase and barium hydroxide as a minor phase during mechanical milling in all three samples. It was observed that the specimen milled for 48 h exhibits the smallest mean crystallite size of 25 nm for hematite, as major phase. XRD results showed that annealing at 1100°C produces more pure barium hexaferrite phase comparing to lower temperatures. So, it was concluded that single phase BaFe₁₂O₁₉ can be achieved by milling for 48 h and then annealing at 1100°C. The sample processed at these conditions exhibited nano-crystalline barium hexaferrite powders with a mean crystallite size of 46 nm, mean particle size of about 200 nm and high coercivity of 334.2 kA/m.