| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 88 === Observations of the mechanisms and possibility of synthesizing ultra-fine Li-Ferrite (LiF) powders via the tartaric acid technique are the major objective of this study. Especially the possibility of Topotatic Reaction (TTR) at low temperature owing to the similar structure between γ-Fe2O3 and LiF.
Synthesis of LiF via tartaric acid technique can have two TTR steps : lithium ions into (1) γ-Fe2O3 around 450℃ and (2) into lithium containing γ-Fe2O3 around 600℃. A suitable pretreatment before 450 and 600℃can result in the completion of TTR, avoiding the occurrence of γ→α-Fe2O3 transformation. Also a pretreatment around 200℃ can simplify the synthesizing mechanism through TTR, because of the more complete decomposition of Li-Fe-tartrates.
As a result, the adequate ways to produce LiF by TTR and avoid γ→α-Fe2O3 transformation can be undertaken by : (1) held at 200℃, which provides sufficient times for tartrates decomposition and favor for the following completion of TTR; (2) held at 300℃, by which a complete formation of LiF from γ-Fe2O3 and lithium ions via TTR can be achieved. This will reduce the amount of γ→α-Fe2O3 transformation; and (3) held at 550℃, by which the formation of LiF from lithium containing γ-Fe2O3 via TTR can be achieved. This will eliminate the occurrence of α-Fe2O3 from lithium containing γ-Fe2O3. Finally heat treatment at 700℃, which makes the residual fine α-Fe2O3 react with lithium ions to produce LiF by conventional solid state reaction. In above-mentioned ways, (1) and (3) can efficiently solve the problems of the occurrences of second phase,α-Fe2O3. The mean grain size of XRD and BET of final production powders are all in the range of nanometers.
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