| Summary: | 碩士 === 國立成功大學 === 資源工程研究所 === 89 === This study discussed the effect of mixing homogeneity during the formation of Li-Ferrite powders by a metal-organo method. The well mixing operation may result in the reduction of formation temperature of products. The Li-Fe coprecipitated gels were obtained via tartaric acid techniques. The resulting solution was pH-adjusted by the addition of NH4OH solution. The samples were obtained by removing the organic volatile portions and heating treatment. Thermal behavior examination of gels and calcination powders were conducted by DTA/TG measurements and crystalline phases were identified by XRD. The mixing homogeneity were evaluated if synthesizing mono-phase Li-Ferrite at low temperature or notα-Fe2O3 will present during heat treatment if the starting materials were not well-mixed. Li-Ferrite. It can be eliminated by controlling the mixing condition of starting materials.
It was found that the Li-Fe coprecipitated gels obtained by pH-adjusted were a mixture of complex metal-organo compound and the mixing homogeneity was improved. By the rising of pH value, FeOOH becomes the main phase instead of Fe tartrates in the system. Simultaneously, the amount of NH4C4H4O6H was raised with the pH value. The organic volatile portions were decomposed completely at higher temperature.
In this study, α-Fe2O3 presented in three conditions : (1) FeOOH dehydrated at the temperature range 200 ~ 300℃. (2) Residualγ-Fe2O3 which react without Li+ ions transformed to α-Fe2O3 at 450℃. (3) Li-containing γ-Fe2O3 decomposed into Li-Ferrite and α-Fe2O3 at 600℃. (1) occurred at pH = 7 and 8. α-Fe2O3 can reacted with Li+ ions to form Li-Ferrite. (2) and (3) occurred at pH = 3, 5, and non-pH-adjusted. Thus, Li-Ferrite was synthesized by conventional solid-state reaction method at high temperature and resulted in coarsed-size powders. Additionally, removing the organic volatile of samples by prethermal treated at 200℃ for 2 hours so as to eliminated the formation of α-Fe2O3.
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