Different phases of iron oxide were obtained by hydrothermal treatment of ferric solution at 200°C with the addition of either KOH, ethylenediamine (EDA), or KOH and EDA into the reaction system. As usually observed, the α-Fe2O3 hexagonal plates and hexagonal bipyramids were obtained for reaction with KOH and EDA, respectively. When both KOH and EDA were added into the reaction system, we observed an interesting phase transformation from α-Fe2O3 to Fe3O4 at low-temperature hydrothermal conditions. The phase transformation involves the formation of α-Fe2O3 hexagonal plates, the dissolution of the α-Fe2O3 hexagonal plates, the reduction of Fe3+ to Fe2+, and the nucleation and growth of new Fe3O4 polyhedral particles.
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机译：通过在200°C的条件下对铁溶液进行水热处理，并向反应体系中添加KOH，乙二胺（EDA）或KOH和EDA，可以得到不同相的氧化铁。如通常所观察到的，获得了分别与KOH和EDA反应的α-Fe2 O 3六角形板和六角形双锥体。当将KOH和EDA都添加到反应体系中时，我们在低温水热条件下观察到了有趣的从α-Fe2O3到Fe3O4的相变。相变包括α-Fe2O3六角形板的形成，α-Fe2O3六角形板的溶解，Fe 3 + 还原为Fe 2 + 和新的Fe3O4多面体颗粒的形核和生长。
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