Low-Temperature Synthesis of MFe₂O₄ (M: Co, Ni, Zn) by Capsule HIP Using Hydroxides as Starting Materials

抄録

The synthesis of MFe₂O₄ (M: Co, Ni and Zn) spinel ferrites was studied by the use of hydroxides as starting materials, applying isostatic pressure of HIP process. Single phases of ZnFe₂O₄ and CoFe₂O₄ were obtained at 300°C. Single phase of NiFe₂O₄ was not obtained at 400°C from the mixture of NiO and FeOOH. However, the mixture of Ni(OH)₂ and FeOOH with 20 mass% of water formed the single phase of NiFe₂O₄ at 400°C. These ferrites revealed high crystallinity and fine particle size of 50–400 nm. No reaction occurred in the mixtures of oxides, such as ZnO and Fe₂O₃. Although the addition of small amount of water to the oxide mixture promoted the reaction, single phase was not obtained at 400°C. In the conventional process, these ferrites were generally prepared at higher temperature of 800–1200°C. Water produced from the hydroxides played important role to form these ferrites at low temperature.