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

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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.
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