Submicron Barium Hexaferrite Ceramics Manufactured by Low-Temperature Liquid-Phase Sintering of BaFe12O19 Nanoparticles

This work has solved the problem of manufacturing high-coercivity barium hexaferrite BaFe12O19 ceramic samples. A BaFe12O19 nanopowder with coercivity H-c = 445 kA/m was prepared by hydrothermal synthesis. Sintering was carried out at low temperature (900 degrees C) to preserve the grains in a single-domain state. To perform sintering at such a low temperature, B2O3 or Bi2O3 was added to the hexaferrite. The effects of the amount and type of additive on the phase composition, microstructure, and magnetic properties of the sintered hexaferrite were studied. When Bi2O3 (in the form of 0.5, 1, or 3 wt % of Bi(NO3)(3)) was used, no changes in the phase composition occurred, while addition of B2O3 (in the form of 0.5, 1, or 3 wt % of H3BO3) resulted in a partial transformation of the hexaferrite to hematite alpha-Fe2O3. The average grain size of BaFe12O19 increased in response to increasing Bi2O3 or B2O3 concentration, but did not exceed the critical single-domain size. This provided for the high Hc values (370-420 kA/m) of the sintered samples, making them superior to most well-known brands of unsubstituted hexaferrites.