Fe Foam Research Articles

Substrate-induced hydrothermal synthesis of hematite superstructures and their Fischer–Tropsch synthesis performance

Fe foam substrates with different pore densities are used to fabricate versatile α-Fe2O3 nanostructures with different Fischer–Tropsch synthesis performance.

Acoustic emission analysis of the compressive deformation of iron foams and their biocompatibility study

We synthesized Fe foams using water suspensions of micrometric Fe2O3 powder by reducing and sintering the sublimated Fe oxide green body to Fe under 5% H2/Ar gas. The resultant Fe foam showed aligned lamellar macropores replicating the ice dendrites. The compressive behavior and deformation mechanism of the synthesized Fe foam were studied using an acoustic emission (AE) method, with which we detected sudden localized structural changes in the Fe foam material. The evolution of the deformation mechanism was elucidated using the adaptive sequential k-means (ASK) algorithm; specifically, the plastic deformation of the cell struts was followed by localized cell collapse, which eventually led to fracturing of the cell walls. For potential biomedical applications, the corrosion and biocompatibility characteristics of the two synthesized Fe foams with different porosities (50% vs. 44%) were examined and compared. Despite its larger porosity, the superior corrosion behavior of the Fe foam with 50% porosity can be attributed to its larger pore size and smaller microscopic surface area. Based on the cytotoxicity tests for the extracts of the foams, the Fe foam with 44% porosity showed better cytocompatibility than that with 50% porosity.

Fabrication of Fe / Al2O3 composite foam by sintering techniques

Composite foams of iron and aluminium oxide were prepared by sintering techniques. Al2O3 microsphere powders added during Fe foam formation were used as starting materials. Samples containing various compositions were prepared (Al2O3 microspheres bonding in Fe foam). The metallic porous structure was obtained by sintering on the basis of iron-based powder mixtures with the addition of a copper catalyst and Fe (III) oxide as a space carrier. Sintering was carried out at 1130°C and 50 minutes long, in a dissociated protective gas with ammonia. Observation of the microstructure and phase identification of the synthesized samples was carried out using optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The porosity of the Fe / Al2O3 composite products for the three different compositions was measured by means of the Cavalleri principle on transverse samples prepared from sintered materials.

Effects of Powder Carrier on the Morphology and Compressive Strength of Iron Foams: Water vs Camphene

With its well-known popularity in structural applications, considerable attention has recently been paid to iron (Fe) and its oxides for its promising functional applications such as biodegradable implants, water-splitting electrodes, and the anode of lithium-ion batteries. For these applications, iron and its oxides can be even further utilized in the form of porous structures. In order to control the pore size, shape, and amount, we synthesized Fe foams using suspensions of micrometric Fe2O3 powder reduced to Fe via freeze casting in water or liquid camphene as a solvent through sublimation of either ice or camphene under 5 pct H2/Ar gas and sintering. We then compared them and found that the resulting Fe foam using water as a solvent (p = 71.7 pct) showed aligned lamellar macropores replicating ice dendrite colonies, while Fe foam using camphene as a solvent (p = 68.0 pct) exhibited interconnected equiaxed macropores replicating camphene dendrites. For all directions with respect to the loading axis, the compressive behavior of the water-based Fe foam with a directional elongated wall pore structure was anisotropic (11.6 ± 0.9 MPa vs 7.8 ± 0.8 MPa), whereas that of the camphene-based Fe foam with a random round pore structure was nearly isotropic (12.0 ± 1.1 MPa vs 11.6 ± 0.4 MPa).

The In Situ Synthesis of Fe(OH)3 Film on Fe Foam as Efficient Anode of Alkaline Supercapacitor Based on a Promising Fe3+/Fe0 Energy Storage Mechanism

AbstractHerein, a simple in situ charge/discharge activation strategy is proposed to synthesize Fe(OH)3 film on Fe foam as an efficient anode of supercapacitors. The physical characteristics of electrodes are characterized and the electrochemical energy storage performances are investigated. Importantly, it is demonstrated the as‐synthesized Fe(OH)3@Fe foam electrode adopted a novel Fe3+/Fe0 redox reaction mechanism for energy storage in alkaline electrolytes. Compared with previously reported Fe3+/Fe2+ mechanisms, the Fe3+/Fe0 redox couple shows a more promising application value (e.g., higher theoretical‐specific capacitance, excellent conductivity of its reduction state). As for supercapacitor anodes, the electrode achieves high areal capacitance of 5.55–3.94 F cm−2 at a current range of 20–200 mA cm−2 and shows good stability for high‐rate and long‐term cycling. The assembled single supercapacitor device gives a high energy density of 11.64–7.43 Wh m−2 at a power density of 157–1461 W m−2. More importantly, the as‐adopted in situ activation strategy may also have potential value for synthesizing other transition metal oxide‐based products.

Preparation and comparative evolution of mechanical behavior of Fe and Fe2O3 foams and their polymer composites

The open cell foams with reticulated structure are cellular materials which is gaining interest in the recent past not only because of scientific interest but also because of their technological importance. By the virtue of their inherent properties derived out of their unique structure, made them promising and rather indispensable materials for wide range of applications. Some of the examples are structural parts, aerospace components, filters, energy absorbing, insulation, catalysis, heat exchangers and energy absorption. In the present investigation, highly porous reticulated open cell iron oxide (Fe2O3) and iron (Fe) foams are successfully fabricated by polymeric sponge replication process. In order to explore the possibility to enhance the energy absorption capability of this cellular materials, Fe2O3 and Fe foams prepared in this study are encapsulated and infiltrated with epoxy polymers which have exhibited an enhancement of weight by 1.45–1.90 times as compare to bare foams. These composite specimens are being metallic/ceramic skeletons with second phase as epoxy polymer on encapsulation/infiltration are expected to fail under stresses with unique mechanisms. This substantially enhances the energy absorption though extend of weight increase is not significant. The bare and composite foam samples were evaluated for quasistatic compression and dynamic impact behavior under identical conditions. On compression, a significant enhancement in energy absorption of 42 and 90 times for Fe2O3 and a less prominent enhancement of 1.3 and 1.95 times in case Fe foams are observed on encapsulation and infiltration respectively. Under dynamic impact an enhancement in energy absorption of 4 and 11 times in case of Fe2O3 and for Fe foam 6.3 and 20.6 times are observed on encapsulation and infiltration respectively. It is evident that energy absorption property is a strong function of material of fabrication, epoxy phase and stress type and conditions. The current study demonstrates an effective way to enhance the mechanical properties of ceramic (Fe2O3) and metallic (Fe) cellular foams through epoxy polymer encapsulation/infiltration process though infiltration have exhibited significant increase in both cases.

Iron-foam as a heterogeneous catalyst in the presence of tripolyphosphate electrolyte for improving electro-Fenton oxidation capability

Fe-Foam (Fe-F) was used as a catalyst in the presence of tripolyphosphate (TPP) electrolyte for electro-Fenton (EF) at circum-neutral pH. Characteristics of Fe-F catalyst were studied by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) and x-ray photoelectron spectroscopy (XPS). Operational conditions (pH and current) influencing H2O2 electrogeneration in TPP electrolyte at a three-dimensional printed gas diffusion electrode (GDE) were systematically investigated. Moreover, linear sweep voltammetry was used to evaluate the system. Results showed that Fe-F, a three-dimensional porous structure catalyst, was covered with Fe2+, Fe3+ and Fe0. The Fe-F/TPP/EF process allowed an 8.55-fold increase in the rate of phenol degradation (used as a model pollutant), higher pseudo-first-order rate constants (6.22 × 10−2 min−1 against 7.30 × 10−3 min−1), a significantly higher mineralization yield (88.69%% against 30% after 8 h electrolysis) and lower energy consumption (0.10 kWhg−1 against 0.98 kWhg−1), as compared to conventional EF process. The high efficiency in Fe-F/TPP/EF was attributed to the following benefits: i) Fe-F was capable of providing Fe2+ ions by chemical corrosion to form Fe2+-TPP complex, which induced the one-electron transfer activation of O2 leading to formation of OH, ii) chemical Fe2+ regeneration combined with Fe0 corrosion provided an additional source of Fe2+ and compensated the low capacity of Fe3+ reduction at GDE, and iii) both surface-mediated and homogeneous reactions contributed to pollutant degradation. The new proposed Fe-F/TPP/EF process displayed promising properties for wastewater treatment applications.

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.

Self-Assembly of Ni–Fe Layered Double Hydroxide on Fe Foam as 3D Integrated Electrocatalysts for Oxygen Evolution: Dependence of the Catalytic Performance on Anions under in Situ Condition

Herein, we demonstrate a very facile self-assembly method to fabricate a Ni–Fe layered double hydroxide (LDH) 3D integrated film at ambient temperature without energy input as a highly efficient electrocatalyst for oxygen evolution reaction (OER). By this method, we can readily regulate the Ni–Fe proportion and change the embedded guest anions into the LDH under our in situ synthetic condition by just using different nickel salts to prepare Ni–Fe LDH. It is found that the Ni–Fe ratio and the embedded guest anions can dramatically influence the corresponding OER catalytic performance. An excellent OER activity that delivering overpotentials of about 210 and 240 mV to reach 10 and 100 mA cm–2 current densities in 1.0 M KOH was achieved.

On-demand oil/water separation of 3D Fe foam by controllable wettability

Oily pollution has become a worldwide problem due to the increasing of oil spill accidents as well as the discharge of oily wastewater. Material with superhydrophobic or underwater superoleophobic characteristic to deal with oily pollution have been reported frequently, but material with controllable wettability transition properties were still few been reported. Herein, we presented a facile, efficient, economical method to prepare a superwetting Fe foam that could achieve controllable wettability transition by modification and annealing alternately. The modified foam showed superhydrophobic and superoleophilic properties (oil-removing mode), which can be used for the filtration of heavy oil in the oil/water mixtures. With the annealing treatment, the as-prepared sample exhibited superhydrophilic/underwater superoleophobic characters (water-removing mode), which allowed water to pass through but blocked light oil. Besides, the as-prepared foam could separate various oil/water mixtures and show high separation efficiency. We are hoping that the controllable wettability filtration sample could realize on-demand oil/water separation and provide a new idea to solve the oil pollution problem.

Electrochemically-induced Reduction of Nitrate in Aqueous Solution

In this study, we evaluated the removal of nitrate from synthetic groundwater by a cathode followed by an anode electrode sequence in the electrochemical flow-through reactor. We also tested the feasibility of the used electrode sequence to minimize the production of ammonia during the nitrate reduction. The performance of monometallic Fe, Cu, Ni and carbon foam cathodes was tested under different current intensities, flow rates/regimes and the presence of Pd and Ag catalyst coating. With the use of monometallic Fe and an increase in current intensity from 60 mA to 120 mA, the nitrate removal rate increased from 7.6% to 25.0%, but values above 120 mA caused a decrease in removal due to excessive gas formation at the electrodes. Among tested materials, monometallic Fe foam cathode showed the highest nitrates removal rate and increased significantly in the presence of Pd catalyst: from 25.0% to 39.8%. Further, the circulation under 3 mL min-1 elevated the nitrate removal by 33% and the final nitrate concentration fell below the maximum contaminant level of 10 mg L-1 nitrate-nitrogen (NO3-N). During the treatment, the yield of ammonia production after the cathode was 92±4% while after the anode (Ti/IrO2/Ta2O5), the amount of ammonia significantly declined to 50%. The results proved that flow-through, undivided electrochemical systems can be used to remove nitrate from groundwater with the possibility of simultaneously controlling the generation of ammonia.

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting.

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm-2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm-2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting

AbstractNanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro‐architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze‐casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm−2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm−2 and an accordingly high incident photon‐to‐current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.

Bimodal NdNiAl and NdFeB hybrid catalytic and magnetic nanoparticles laminated on Fe foam: catalytic conversion of CO + 3H2 to CH4

For the production of CH4 from CO hydrogenation, a hybrid foam with high catalytic activity and strong magnetic bonding ability was fabricated by electrospraying and co-sintering NdNiAl and NdFeB nanoparticles over a Fe foam.

The Effect of Mixing Ratios on Pore Properties of Fe Foam Fabricated Using Slurry Coating Process

Metal foams have a cellular structure consisting of a solid metal containing a large volume fraction of pores. In particular, open, penetrable pores are necessary for industrial applications such as in high temperature filters and as support for catalysts. In this study, Fe foam with greater than 90% porosity, 2-mm pore size was successfully fabricated using a slurry coating process and the pore properties were characterized. The Fe and Fe2O3 powder mixing ratios were controlled to produce Fe foam samples with different pore sizes and porosity. First, the slurry was prepared through the uniform mixing of powders, distilled water, and polyvinyl alcohol (PVA). The amount of slurry coated on the PU foam increased with theFe2O3 mixing powder ratio, but the shrinkage and porosity of the Fe foams decreased, respectively, with increasing Fe2O3 mixing powder ratio.

Processing, Microstructure, and Oxidation Behavior of Iron Foams

With its historically long popularity in major structural applications, the use of iron (Fe) has also recently begun to be explored as an advanced functional material. For this purpose, it is more advantageous to use Fe as a porous structure, simply because it can provide a greater surface area and a higher reaction rate. This study uses a freeze-casting method, which consists of simple and low-cost processing steps, to produce Fe foam with a mean pore size of 10 μm. We examine the influences of various parameters (i.e., mold bottom temperature, powder content, and sintering time) on the processing of Fe foam, along with its oxidation kinetics at 823 K (550 °C) with various heat-treatment times. We confirm that Fe2O3 and Fe3O4 oxide layers are successfully formed on the surface of Fe foam. With the Fe oxide layers as an active anode material, the Fe foam can potentially be used as a three-dimensional anode current collector for an advanced lithium-ion battery.

The influence of cathode material on electrochemical degradation of trichloroethylene in aqueous solution

In this study, different cathode materials were evaluated for electrochemical degradation of aqueous phase trichloroethylene (TCE). A cathode followed by an anode electrode sequence was used to support reduction of TCE at the cathode via hydrodechlorination (HDC). The performance of iron (Fe), copper (Cu), nickel (Ni), aluminum (Al) and carbon (C) foam cathodes was evaluated. We tested commercially available foam materials, which provide large electrode surface area and important properties for field application of the technology. Ni foam cathode produced the highest TCE removal (68.4%) due to its high electrocatalytic activity for hydrogen generation and promotion of HDC. Different performances of the cathode materials originate from differences in the bond strength between atomic hydrogen and the material. With a higher electrocatalytic activity than Ni, Pd catalyst (used as cathode coating) increased TCE removal from 43.5% to 99.8% for Fe, from 56.2% to 79.6% for Cu, from 68.4% to 78.4% for Ni, from 42.0% to 63.6% for Al and from 64.9% to 86.2% for C cathode. The performance of the palladized Fe foam cathode was tested for degradation of TCE in the presence of nitrates, as another commonly found groundwater species. TCE removal decreased from 99% to 41.2% in presence of 100 mg L−1 of nitrates due to the competition with TCE for HDC at the cathode.The results indicate that the cathode material affects TCE removal rate while the Pd catalyst significantly enhances cathode activity to degrade TCE via HDC.

Fe and Fe-P Foam for Biodegradable Bone Replacement Material: Morphology, Corrosion Behaviour, and Mechanical Properties

Iron and iron-phosphorus open-cell foams were manufactured by a replica method based on a powder metallurgical approach to serve as a temporary biodegradable bone replacement material. Iron foams alloyed with phosphorus were prepared with the aim of enhancing the mechanical properties and manipulating the corrosion rate. Two different types of Fe-P foams containing 0.5 wt.% of P were prepared: Fe-P(I) foams from a phosphated carbonyl iron powder and Fe-P(II) foams from a mixture of carbonyl iron and commercial Fe3P. The microstructure of foams was analyzed using scanning electron microscopy. The mechanical properties and the corrosion behaviour were studied by compression tests and potentiodynamic polarization in Hank’s solution and a physiological saline solution. The results showed that the manufactured foams exhibited an open, interconnected, microstructure similar to that of a cancellous bone. The presence of phosphorus improved the mechanical properties of the foams and decreased the corrosion rate as compared to pure iron foams.

A Study on the Effect of Binder Content for Pore Property of Fe Foam Using Slurry Coating Method

Fe foam with above 90% porosity and 2 millimeter pore size was successfully fabricated by a slurry coating process. In this study, the binder contents were controlled to produce the Fe foam with different pore size, strut thickness and porosity. Firstly, the slurry was prepared by uniform mixing with Fe powders, distilled water and polyvinyl alcohol (PVA) as initial materials. After slurry coating on the polyurethane (PU) foam the sample was dried at 80°C. The PVA and PU foams were then removed by heating at 700°C for 3 hours. The debinded samples were subsequently sintered at 1250°C with holding time of 3 hours under hydrogen atmosphere. The three dimensional geometries of the obtained Fe foams with open cell structure were investigated using X-ray micro CT(computed tomography) as well as the pore morphology, size and phase.

Characterisation and electrochemical behaviour of electrodeposited Cu–Fe foams applied as pseudocapacitor electrodes

Copper–iron (Cu–Fe) 3D porous foams for supercapacitor electrodes were electrodeposited in the cathodic regime, on stainless steel current collectors, using hydrogen bubbling dynamic template. The foams were prepared at different current densities and deposition times. The foams were submitted to thermal conditioning at temperatures of 150 and 250°C. The morphology, composition and structure of the formed films were studied by SEM, EDS and XRD, respectively. The electrochemical behaviour was studied by cyclic voltammetry, electrochemical impedance spectroscopy and chronopotentiometry.The morphology of the 3D Cu–Fe foams is sensitive to the electrodeposition current and time. The increase of the current density produces a denser, larger and more ramified dendritic structure. Thermal conditioning at high temperature induces a coarser grain structure and the formation of copper oxides, which affect the electrochemical behaviour.The electrochemical response reveals the presence of various redox peaks assigned to the oxidation and reduction of Cu and Fe oxides and hydroxides in the foams. The specific capacitance of the 3D Cu–Fe foams was significantly enhanced by thermal conditioning at 150°C. The highest specific capacitance values attained 297Fg−1 which are much above the ones typically observed for single Cu or Fe oxides and hydroxides. These values highlight a synergistic behaviour resulting from the combination of Cu and Fe in the form of nanostructured metallic foams. Moreover, the capacitance retention observed in an 8000 charge/discharge cycling test was above 66%, stating the good performance of these materials and its enhanced electrochemical response as supercapacitor negative electrodes.