Transmission electron microscopy study of barium hexaferrite formation from barium carbonate and hematite

The formation of barium hexaferrite from stoichiometric mixtures of BaCO3 a nd Fe2O3 has been investigated by means of differential thermal analysis an d thermogravimetry, x-ray diffraction, and transmission electron microscopy -energy dispersive spectrometry. The first step, which implies decarbonatat ion and monoferrite formation, includes the formation of various intermedia te compounds, which are formed at contact points between BaCO3 and Fe2O3 gr ains, and implies diffusion of both species. In the second step, barium hex aferrite is formed at interfaces between monoferrite and iron oxide mainly by diffusion of barium through the BF6 lattice into the hematite lattice. T his exothermic reaction process leads to nonagglomerated pseudohexagonal pl atelets with an average particle size very close to the one of the starting powder mixture (similar to 1 mu m).