Study of formation mechanism of barium hexaferrite by sintering curve

Barium hexaferrite (BaFe12O19) with hexagonal structure was fabricated by sintering the mixture of α-Fe2O3 and BaCO3, ball milling of the mixture followed by heat treatment as well as glycin–nitrate method and subsequent heat treatment, respectively. The mechanism of formation of the BaFe12O19 in the three kinds of procedures was investigated by using sintering shrinkage curve and XRD measurements. It was found that the α-Fe2O3 reacted with BaCO3 to form BaFe2O4 with orthorhombic structure as the mixture were sintered above 660 °C firstly and then the BaFe2O4 reacted with α-Fe2O3 to form BaFe12O19 in a sintering temperature ranging from 770 to 920 °C. However, the α-Fe2O3 reacted with BaCO3 to form BaxFe3−xO4 with spinel structure when the mixture was milled for 80 h, while the BaFe12O19 was obtained by annealing the BaxFe3−xO4 at 700–1000 °C. In the glycin–nitrate procedure, the precursor powders containing α-Fe2O3, Fe3O4 and BaFe2O4 were fabricated by self-propagating reaction firstly, and then the single BaFe12O19 was produced by sintering the precursor powders at 1000 °C. The magnetic properties of the BaFe12O19 produced by the three kinds of procedures were reached. The saturation magnetization and the coercivity of the BaFe12O19 fabricated by ball milling followed by heat treatment were 47.24 emu/g and 5086.34 Oe, respectively, which were much larger than those of the BaFe12O19 produced by other procedures. The mechanism leading to that the BaFe12O19 produced by the different methods had different magnetic properties was discussed in the present work.