Abstract
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.
Highlights
Reticulated sponges made of polyurethane (PU) have been commercially available since the1950s [1]
Fully-compact pore walls were observed in the foams produced from the Fe- and FeMn-containing slurries obtained at the lowest N2 flow (Figure 1a,b); at larger N2 flows, the pore walls exhibit a nanoporous morphology the distribution and the size of the big pores was not compromised
Porous foams with homogeneous open-cell structure have been obtained by the replication process using polyurethane templates
Summary
Reticulated sponges made of polyurethane (PU) have been commercially available since the1950s [1]. The first attempts to transfer porous templates into ceramic (i.e., oxide) foams by the powder slurry replication method date from early 1960s [2]. The method has become widely available for many applications involving porous oxide materials: electromagnetic wave absorbers, gas sensors, catalysts, oil-water separators and lithium-ion batteries [3,4,5,6,7,8]. The polymeric sponge replication process has consolidated as a promising technique to create cellular oxide structures with 3D interconnected pores, characterized by high strength and high corrosion resistance in acid and alkaline media [9,10,11]. Materials 2018, 11, 280 by this method and they found applications such as battery electrodes, catalysts or filters [12,13,14]. Over the past ten years, the replication method has been extended to manufacture porous steels [15,16,17,18]
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