Synthesis of α-Fe2O3 and Fe-Mn Oxide Foams with Highly Tunable Magnetic Properties by the Replication Method from Polyurethane Templates

Open cell foams consisting of Fe and Fe-Mn oxides are prepared from metallic Fe and Mn powder precursors by the replication method using porous polyurethane (PU) templates. First, reticulated PU templates are coated by slurry impregnation. The templates are then thermally removed at 260 °C and the debinded powders are sintered at 1000 °C under N₂ atmosphere. The morphology, structure, and magnetic properties are studied by scanning electron microscopy, X-ray diffraction and vibrating sample magnetometry, respectively. The obtained Fe and Fe-Mn oxide foams possess both high surface area and homogeneous open-cell structure. Hematite (α-Fe₂O₃) foams are obtained from the metallic iron slurry independently of the N₂ flow. In contrast, the microstructure of the FeMn-based oxide foams can be tailored by adjusting the N₂ flow. While the main phases for a N₂ flow rate of 180 L/h are α-Fe₂O₃ and FeMnO₃, the predominant phase for high N₂ flow rates (e.g., 650 L/h) is Fe₂MnO₄. Accordingly, a linear magnetization versus field behavior is observed for the hematite foams, while clear hysteresis loops are obtained for the Fe₂MnO₄ foams. Actually, the saturation magnetization of the foams containing Mn increases from 5 emu/g to 52 emu/g when the N₂ flow rate (i.e., the amount of Fe₂MnO₄) is increased. The obtained foams are appealing for a wide range of applications, such as electromagnetic absorbers, catalysts supports, thermal and acoustic insulation systems or wirelessly magnetically-guided porous objects in fluids.