| Summary: | 碩士 === 淡江大學 === 化學工程學系 === 88 === A citric acid precursor method was used to prepare MnFe2O4 and (Mn,Zn)Fe2O4 particles. Citric acid was added into an aqueous solution, containing nitrates of iron, manganese, or zinc in stoichiometric ratios to form the required ferrites, to chelate the metallic ions. The pH values of starting aqueous solutions were adjusted using NH4OH. After adding glycol into the solution and raising the solution temperature to 353 K, esterification caused the formation of the required solid precursors. The dried solid precursors so obtained were then pyrolyzed to form the corresponding oxides. The characteristics of the obtained solid powders were studied using XRD, TEM, and SEM. Crystalline submicron MnFe2O4 powders were obtained at 623 K for all pH values of the starting solutions used. In air, Mn2+ in MnFe2O4 powder was oxidized to form Mn3+ at temperatures about 873 K, resulting in phase segregation. The addition of Zn2+ or Mg2+ in the starting solution effectively, in some extent, prevented the oxidation of Mn2+. The addition of Zn2+ and Mg2+ may create and increase point defects in the ferrite structure, by forming the Mn2+-Zn2+-oxide and Mn2+-Mg2+-oxide solid solution, and slow down the oxidation process of Mn2+ in air. The best composition in preparing MnFe2O4 with good soft magnetic properties is the one with 5% Mg2+ additions. Particles obtained by citric acid precursor method have high sinterbility and MnFe2O4 powder can be sintered at 1273 K in vacuum.
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