title: Hydrothermal phase transformation of hematite to magnetite.
abstract: 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 Fe(3+) to Fe(2+), and the nucleation and growth of new Fe3O4 polyhedral particles.
authors.affiliation: Department of Material Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan.
authors.forename: Jie-Feng
authors.initials: JF
authors.lastname: Lu
authors.affiliation: Department of Material Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan.
authors.forename: Cho-Jen
authors.initials: CJ
authors.lastname: Tsai
keywords: Hydrothermal; Iron oxides; Phase transformation