Hydrothermal synthesis of barium hexaferrite

Abstract

The authors of the report carried out synthesis of barium hexaferrite (BHF) both in water vapor atmosphere and in liquid medium in the temperature range 200-400°C at pressures PH₂O of 9-26MPa in laboratory autoclaves. The results of research have shown that BHF with the best performances can be obtained by thermovaporous treatment of dry mixtures of precursors (γ-F₂O₃ with barium hydroxide or nitrate). As Fe - containing precursor, α-FeOOH can be also used. The formation of BHF begins at the temperature of about 200° C. The BHF crystals are hexagonal platelets with diameter ≥ 1 μm and thickness 0,1 −0,2 μm. The magnetic properties of synthesized BHF can be improved by increasing the temperature of thermovapor treatment. The coercive forces of the BHF samples synthesized at about 400°C vary from 1.7-2.0 kOe and spec& saturation magnetization of nonoriented samples from 40-50emu/g. BHF crystals with low coercive force (0.6-0.7) kOe were obtained by introduction of doping micro-additives at the stage of their formation in water vapor atmosphere.

Key Words:

• Barium hexaferrite
• Hydrothermal synthesis
• Specific saturation magnetization
• Coercive force