Synthesis of <I>α</I>-Fe<SUB>2</SUB>O<SUB>3</SUB> Templates via Hydrothermal Route and Fe<SUB>3</SUB>O<SUB>4</SUB> Particles Through Subsequent Chemical Reduction

FeCl3–NH4H2PO4 system was employed to fabricate -Fe2O3 nanoparticles by a hydrothermal method. The results showed that the most important factors affecting the size and morphology of as-prepared -Fe2O3 particles were the reactant concentration and the molar ratio of iron precursor to additives, i.e., [Fe]/[H2PO4 ]. Besides -Fe2O3 rings and tubes, single-crystalline -Fe2O3 rods with controllable size were successfully fabricated by adjusting the [Fe]/[H2PO4 ] ratio. The formation mechanism for -Fe2O3 nanocrystals with different shapes was studied. In order to produce Fe3O4 particles (in ring, tube or rod shapes), the as-prepared -Fe2O3 particles were employed as templates. Phase conversion from hematite to magnetite was achieved via a chemical reduction method. In this reduction process, both surfactants (oleic acid) and protective gas (5% H2/95% Ar gas mixture) were used as reduction agents. The effect of oleic acid and H2 gas on the reduction process of -Fe2O3 particles was studied through a series of experiments. The results indicated that the chemical reduction method was convenient and feasible to reduce various hematite templates to corresponding magnetite nanostructures.