The formation of barium hexaferrites using coprecipitation methods

The mechanism of the barium-hexaferrite formation using coprecipitation is investigated. Also, the influence of various parameters on its formation and correlated them with the reaction kinetics is studied. Solutions of stoichiometric amount of Ba (II), Fe (III) and Co (II) salts in water, ethanol or isopropanol are coprecipitated with NaOH at pH 13, normally in air or under constant flow of Ar. The precursors are calcined at 300-800°C for 10 h and the resulting powders are sintered at 1200°C. The synthesis is monitored with thermogravimetric and differential thermal analyses, X-ray powder diffraction and electron microscopy. The formation of Ba₂Co₂Fe₁₂O₂₂ is lower by several hundreds of °C when coprecipitation is accomplished with ethanol under the Ar flow. Ceramics with a minimum of 90% relative density are obtained at 1200°C without any sintering aids. A homogenous microstructure and exaggerated grain growth, typical for hexaferrites, is sufficiently suppressed. Also, the ceramics exhibit a natural ferromagnetic resonance at 4-6 GHz.