Relationship between Crystal Structure of Inclusions and Formation of Acicular Ferrites

The formation mechanism of intragranular ferrites with acicular morphology was discussed. The ferrites were characterized by scanning electron microscopy. The results showed that the ferrites had an acicular structure with radial, symmetrical, and acicular laths, and that the inclusions were the nucleation sites of the intragranular acicular ferrites. Transmission electron microscopy (TEM) was used to characterize the inclusions. The results of TEM with energy dispersive spectroscopy and TEM-selected area electron diffraction indicated that the complex inclusions consisted of Ti-Al complex oxides and MnS. The jagged edges of the complex inclusions can be ascribed to the effects of the crystal structure. The stabilization energy U of the coordination polyhedron growth units varies with the type of connection according to the calculation results. A larger U corresponds to more stable growth units, which induces the preferentially oriented growth of inclusions, at which point acicular ferrites are formed.