| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 104 === Phase transform of α-Fe2O3 to Fe3O4 were observed by hydrothermal treatment of ferric solution at 160-220 oC with the addition of both KOH and EDA into the reaction system. The reactions began with the formation of α-Fe2O3 hexagonal plates followed by the phase transformation involving dissolution of the α-Fe2O3 hexagonal platelets, the reduction of Fe3+ to Fe2+, and the nucleation and growth of new Fe3O4 polyhedral particles. The activation energies for the phase transformation of α-Fe2O3 to Fe3O4 in hydrothermal condition are estimated to be 96.411, 113.15, and 118.311 kJ/mol for the case of addition of 0.5, 1 and 1.5 ml of EDA, respectively, which are about the same for typical phase transformation of α-Fe2O3 to Fe3O4 in hydrogen ambient. Hematite (α-Fe2O3) nanoparticles with irregular polyhedron, hexagonal bipyramid, elongated bipyramid, and rhombohedron shapes were prepared by hydrothermal treatment of ferric solution at 180 oC with the addition of different amount of water to EDA ratio in the reaction systems. The electrochemical measurements of these different particle shapes as materials for lithium ion battery showed that the best performance both in specific capacity and rate capacity were observed to be the shape of hexagonal bipyramid. The results show that, beside the size of the particles, the shape of the particles which is confined with specific surfaces is another important factor that dictates the electrochemical performance of α-Fe2O3.
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