Preparation Of Hexagonal Barium Ferrite

The hexagonal barium ferrite is magnetic material, which has been widely used in the field of high-density magnetic recording media and information field absorbing materials because of their magnetic anisotropy, excellent spin magnetic characteristics and good chemical stability. Recent studies show that the performance of barium ferrite is closely related with not only its purity and crystallinity, but also their morphology. When barium ferrite particles are flake or rod-like, the absorbing performance of barium ferrite is relatively increased and absorbing performance of sheet barium ferrite is slightly better than the rod-like barium ferrite.In this article, the sheet barium ferrite was prepared by coprecipitation, salt-melt method, sol-gel method and hydrothermal synthesis. We focused on the optimum reaction ratio of iron ions with barium ions and reaction condition for the different synthesis methods. The study showed when barium ferrite was prepared by different methods, the ratio of iron ions with barium ions was generally non-stoichiometric. The phase and microstructure of barium ferrite ware characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM).When barium ferrite was prepared by coprecipitation, the different precipitation solutions have great influence on the morphology of barium ferrite. Using sodium carbonate as precipitating liquid, the more regular sheet structure was generated. When the ratio of iron ions with barium ions was10, using sodium as carbonate precipitant solution, and the precursor was calcined at800℃for3h, single phase hexagonal barium ferrite was obtained.Due to molten salt restricted grain agglomeration and grow, when barium ferrite was prepared by salt-melt method, molten salt was often added to the precursor. In this experiment, the KCl and NaCl were used as molten salt. The experiment showed when used KCl as molten salt, the barium ferrite had good crystallinity. When the ratio of the quality of the added sodium chloride and precursor was1, the hexagonal barium ferrite was prepared. With increasing KCl content, equivalent diameter of barium ferrite increased from300nm to400nm, but the thickness of barium ferrite basically unchanged, so the aspect ratio of barium ferrite become larger.The sheet barium ferrite was prepared by sol-gel method when EDTA and glycol were added into reaction solution. When the molar ratio of iron ions with barium ions was different, sheet barium ferrite was prepared by different sintering system. When the molar ratio of iron ions with barium ions was10.5, the single phase barium ferrite was prepared by heating precursor to850℃for4h. When the molar ratio of iron ions with barium ions was12, the single phase barium ferrite was prepared by heating precursor to850℃for1h.When preparing barium ferrite by hydrothermal synthesis, sodium hydroxide was used as mineralizing agent and the amount of sodium hydroxide affected the morphology of barium ferrite. The amount of sodium hydroxide was changed when the proportion of hydroxide and nitrate changed. When the molar ratio of iron ions with barium ions was10.5, the ratio of hydroxide and nitrate was6, the sheet barium ferrite was obtained.Four kinds of methods for preparing barium ferrite, the barium ferrite, which is hexagonal plate, uniform size and high yields,is prepared by salt-melt method.