Iron Foams Research Articles

Development of Triply Periodic Minimal Surface (TPMS) Inspired Structured Cast Iron Foams through Casting Route

Development of Triply Periodic Minimal Surface (TPMS) Inspired Structured Cast Iron Foams through Casting Route

Activated M,S co-doping (M = Ni, Co, Mn) inverse spinel oxides with mixed mechanisms for water oxidation

Inverse spinels with characteristic structures are one of the most popular electrocatalytic materials, but typically have limited intrinsic activities for oxygen evolution reactions (OER). Here, taking the conventional inverse spinel Fe3O4 as an example, a series of M (M = Ni, Co, Mn) and S co-doped Fe3O4 OER catalysts are selected by the guidance from theoretical simulations, and then experimentally verified by hydrothermally growing M and S co-doped Fe3O4 on iron foams (M,S-Fe3O4/IF). Based on experimentally and theoretically investigating their OER performance, M,S-Fe3O4/IF are considered to follow mixed OER mechanisms including adsorbate evolution mechanism and lattice oxygen mechanism, and Ni,S-Fe3O4/IF and Co,S-Fe3O4/IF display low overpotentials of 276 and 300 mV at 100 mA cm-2, respectively. Particularly, the Co atoms into S-Fe3O4/IF serve as promoters for in-situ Fe dissolution and redeposition of electrochemical reconstruction during alkaline OER processes. This work contributes new avenues for designing spinel-type materials with mixed OER mechanisms.

Anticorrosive superhydrophobic high-entropy alloy coating on 3D iron foam for efficient oil/water separation

Oil-spill remediation requires low-cost, high-efficiency, and operationally flexible oil-water separators, particularly those with superior corrosion resistance to extend their service life. Superhydrophobic 3D metallic foams are increasingly attracting tremendous attention due to their excellent mechanical stability and promising applications for continuous in-situ separation. Hence, superhydrophobic iron foams were fabricated via cyanide-free electrodeposition of a ZnFeCoNiMn high-entropy alloy (HEA) coating followed by non‑fluorine surface modification with tetradecanoic acid. Fluffy microspheres with hierarchical micro/nanostructure on the superhydrophobic HEA coating contributed to the superhydrophobicity of 3D iron foam. These foams exhibited highly efficient separation of oil and water even under violent stirring (700 rpm). Moreover, they achieved excellent anti-corrosion performance, with a decline in corrosion rate from 14.95 to 0.27 mm·a−1 in a 3.5 wt% NaCl solution, making it perfect for the harsh sea environment.

Directional Reconstruction of Iron Oxides to Active Sites for Superior Water Oxidation

AbstractRationally constructing and manipulating the in situ formed catalytically active surface of catalysts remains a tremendous challenge for a highly efficient water electrolysis. Herein, an anion and cation co‐induced strategy is presented to modulate in situ catalyst dissolution‐redeposition and to achieve the directional reconstruction of Zn and S co‐doped Fe2O3 and Fe3O4 on iron foams (Zn,S‐Fe2O3‐Fe3O4/IF), for oxygen evolution reaction (OER). Benefiting from Zn, S co‐doping and the presence of Fe3O4, a directionally reconstructed surface is obtained. The Fe2O3 in the Zn,S‐Fe2O3‐Fe3O4/IF is directionally reconstructed into FeOOH (Zn,S‐Fe3O4‐FeOOH/IF), in which the S leaching promotes the Fe dissolution and the Zn co‐deposition regulates the activity of the obtained FeOOH. Moreover, the presence of Fe3O4 provides a stable site for FeOOH deposition, and thus causes more FeOOH active components to be formed. Directionally reconstructed Zn,S‐Fe3O4‐FeOOH/IF outperformes many state‐of‐the‐art OER catalysts and demonstrates a remarkable stability. The experimental and density functional theory (DFT) calculation results show that the introduction of Zn‐doped FeOOH with abundant oxygen vacancies through directional reconstruction has activated lattice O atoms, facilitating the OER process on the heterojunction surface following the lattice oxygen mechanism (LOM) pathway. This work makes a stride in co‐induced strategy modulating directional reconstruction.

Comparative Study of Porous Iron Foams for Biodegradable Implants: Structural Analysis and In Vitro Assessment.

Biodegradable metal systems are the future of modern implantology. This publication describes the preparation of porous iron-based materials using a simple, affordable replica method on a polymeric template. We obtained two iron-based materials with different pore sizes for potential application in cardiac surgery implants. The materials were compared in terms of their corrosion rate (using immersion and electrochemical methods) and their cytotoxic activity (indirect test on three cell lines: mouse L929 fibroblasts, human aortic smooth muscle cells (HAMSC), and human umbilical vein endothelial cells (HUVEC)). Our research proved that the material being too porous might have a toxic effect on cell lines due to rapid corrosion.

Sulphur-dopant induced breaking of the scaling relation on low-valence Ni sites in nickel ferrite nanocones for water oxidation with industrial-level current density

The microstructure of active centers in bimetallic/multimetallic catalysts is under a long-time debate toward oxygen evolution reaction (OER). Here, sulfur doping NiFe2O4 nanocone arrays on iron foams (S-NiFe2O4/IF) is prepared via a scalable hydrothermal method. The favorable 3D nanocone arrays can offer large electrochemical surface area and allow for effective electrolyte access and O2 escape. Physical characterizations confirm low-valence Ni atoms in tetrahedron sites are more actives sites than high-valence Fe atoms in this S-doped bimetallic catalyst. Meanwhile, DFT calculations further verify the S introduction enhances the adsorption and dissociation of water, and optimizes the adsorption of OER intermediates on Ni sites. Therefore, the optimal S-NiFe2O4/IF achieves industrial-level 500 mA cm−2 at an overpotential of only 310 mV and maintains for 100 h in an alkaline medium. In addition, integrating S-NiFe2O4/IF into an anion-exchange membrane water electrolyzer can deliver a current density of 1.0 A cm−2 at 1.79 V.

Highly porous FeNi 3D foams produced by one-step electrodeposition: Electrochemical stability and mechanical properties

Highly porous iron‑nickel foams, including the first-ever reported pure iron foam, were prepared by the dynamic hydrogen bubble template electrodeposition method and studied regarding their electrochemical stability and mechanical properties. Changes on the morphology, microstructure, and electrochemical resistance of the foams were investigated as a function of the Fe:Ni ratio by scanning electron microscopy (SEM), d.c. polarization and electrochemical impedance spectroscopy (EIS). Tensile and bending tests were carried out to evaluate the mechanical behavior of the prepared foams. Both crystalline structure and morphology are affected by the increase of Ni content, evolving from a highly porous foam with a body-centered cubic (bcc) structure to a denser material with open pores and face-centered cubic (fcc) structure. Polarization curves reveal an ennoblement of the corrosion potential as the nickel content increases. The impedance response revealed a dependence on the foam porosity. An increased number of pores was found more detrimental to the mechanical properties of the foams, as fractures seem to propagate, preferentially by cracks due to connecting pores. As result, foams with higher Ni contents displayed better mechanical performance for both tensile and bending assays. Results show that this innovative and powerfull technique enables to design iron foams with the adequate properties required for industrial applications. • Fe and FeNi nanofoams are prepared by Dynamic Hydrogen Bubble Template Electrodeposition. • Pure iron foam is obtained for the first time. • Foams morphology change for higher Ni contents. • Faradaic resistance depends on both %Fe and the pore availability. • Improved mechanical resistance is observed for the less porous foams.

Experimental study on heat transfer characteristics of metal foam/paraffin composite PCMs in large cavities: Effects of material types and heating configurations

This study explores the effects of material types and structural parameters of metal foam, and heating configurations on the evolution of melting front, heat transfer characteristics, and temperature distribution of metal foam/paraffin composite phase change materials (PCMs) in large cavities. Copper and iron foams were used as the heat transfer enhancement medium, while paraffin with a melting point of 45 °C was chosen as the PCM to store heat. This study identified the heat transfer regimes in large cavities during the melting process. The experimental results on different heating configurations indicated that different from small cavities, both conduction and convection regimes played a fundamental role in the melting process. In addition, the heating configuration controlled the evolution of the melting front of the pure PCM and composite PCM. On the basis of these results, a non-dimensional correlation validated against a large dataset of experiments was fitted to model the melting process of the composite PCMs.

Combined Effect of Phosphate and Polymer Coating on Cytotoxicity and Hemocompatibility of Iron Foams

Abstract The use of resorbable metallic biomaterials for temporary implants has increased dramatically in the last decade. Degradable biomaterials are desirable in some specific pediatric, orthopedic, and cardiovascular applications, in which they may overcome the disadvantages of permanent devices. The three main biodegradable metals: Mg, Fe, and Zn, are intensively studied as temporary orthopedic implant materials. Among them, iron, and iron-based alloys, have received attention as promising materials for the temporary replacement of bones, especially for applications where strong mechanical support during the bone healing process is required. The addition of a low amount of phosphorus can improve the mechanical properties of such materials without the risk of retarding the corrosion rate or affecting cell proliferation. The main goal of this work was to study the combined effect of phosphating and polymer coating of open-cell iron foams on their cytotoxicity and hemocompatibility. Obtained results indicated the positive influence of the PEG coating layer and phosphorus addition on material cytocompatibility. Moreover, the combination of these procedures led to the inhibition of hemolysis, platelet adhesion, and thrombus formation.

Modeling of Complex Gray Cast Iron Open‐Cell Foams Revealing Insights on Failure and Deformation on Different Hierarchical Length‐Scales

Open‐cell gray cast iron foams are a class of porous materials of increasing interest, with great potential to be used in energy damping applications and for sound isolation. We created finite element (FE) models from 3D reconstructed data of foams and of isolated struts imaged with resolutions spanning from 0.65 to 10.5 μm. Representative volume elements (RVE) are loaded in tension to simulate and analyze foam mechanical behavior. A ductile damage model is used for tensile testing of single struts and compression testing of foams. RVEs loaded along three axes demonstrate important effects of orientation of graphite particles in the microstructure. Only simulation results that take failure into consideration are consistent with experimental findings. Strut fracture initiation strongly depends on the cross‐sectional area and its circularity and foam simulation results are heavily influenced by damage modeling. The complexity of the open‐cell foam behavior is revealed at several hierarchical levels. Simulations in which material properties are assigned excluding damage overestimate the experimental results of the foam; conversely, a very good agreement is observed if damage is considered. The models exhibiting anisotropic mechanical properties fully reproducing large fluctuations in the mechanical properties of the struts are observed in in situ experiments.

Syntactic Iron Foams' Properties Tailored by Means of Case Hardening via Carburizing or Carbonitriding.

Metal foam inserts are known for their high potential for weight and vibration reduction in composite gear wheels. However, most metal foams do not meet the strength requirements mandatory for the transfer of sufficiently high levels of torque by the gears. Syntactic iron and steel foams offer higher strength levels than conventional two-phase metal foams, thus making them optimum candidates for such inserts. The present study investigates to what extent surface hardening treatments commonly applied to gear wheels can improve the mechanical properties of iron-based syntactic foams. Experiments performed thus focus on case hardening treatments based on carburizing and carbonitriding, with subsequent quenching and tempering to achieve surface hardening effects. Production of samples relied on the powder metallurgical metal injection molding (MIM) process. Syntactic iron foams containing 10 wt.% of S60HS hollow glass microspheres were compared to reference materials without such filler. Following heat treatments, the samples’ microstructure was evaluated metallographically; mechanical properties were determined via hardness measurements on reference samples and 4-point bending tests, on both reference and syntactic foam materials. The data obtained show that case hardening can indeed improve the mechanical performance of syntactic iron foams by inducing the formation of a hardened surface layer. Moreover, the investigation indicates that the respective thermo-chemical treatments can be applied to composite gear wheels in exactly the same way as to monolithic ones. In the surface region modified by the treatment, martensitic microstructures were observed, and as consequence, the bending limits of syntactic foam samples were increased by a factor of three.

Post-corrosion mechanical properties of absorbable open cell iron foams with hollow struts

In-depth analyses of post-corrosion mechanical properties and architecture of open cell iron foams with hollow struts as absorbable bone scaffolds were carried out. Variations in the architectural features of the foams after 14 days of immersion in a Hanks’ solution were investigated using micro-computed tomography and scanning electron microscope images. Finite element Kelvin foam model was developed, and the numerical modeling and experimental results were compared against each other. It was observed that the iron foam samples were mostly corroded in the periphery regions. Except for quasi-elastic gradient, other mechanical properties (i.e. compressive strength, yield strength and energy absorbability) decreased monotonically with immersion time. Presence of adherent corrosion products enhanced the load-bearing capacity of the open cell iron foams at small strains. The finite element prediction for the quasi-elastic response of the 14-day corroded foam was in an agreement with the experimental results. This study highlights the importance of considering corrosion mechanism when designing absorbable scaffolds; this is indispensable to offer desirable mechanical properties in porous materials during degradation in a biological environment.

Introduction - Porous Metals: From Nano to Macro - CORRIGENDUM

The volume/issue for reference 25 of this article1 was published incorrectly; the citation should appear as follows: 25. P. Lloreda-Jurado, S. Wilke, K. Scotti, A. Paul-Escolano, D. Dunand and R. Sepulveda: Structure–processing relationships of freeze-cast iron foams fabricated with various solidification rates and post-casting heat treatment J. Mater. Res., 35(19), 2587–2596 (2020).

Biodegradable Iron-Based Foams for Potential Bone Replacement Material

Iron and iron-phosphorus open-cell foams were tested for their potential use as synthetic bone graft substitutes. The samples were manufactured using a replica method based on a powder metallurgical approach. Iron foams alloyed with 0.5 wt. % of phosphorus were prepared with the aim of enhancing the mechanical properties and manipulating the corrosion rate. The manufactured foams were tested for their microstructure, porosity, corrosion behaviour and mechanical properties. SEM analyses of the foams’ microstructures confirmed the presence of an open, three-dimensional interconnected macroporous network similar to that of the human bone. The corrosion behaviour was studied by a static immersion test and potentiodynamic polarisation in Hank’s solution. The results showed that the presence of phosphorus slightly decreased the corrosion rate as compared to pure iron foams. The mechanical properties studied by a compression test confirmed a positive effect of phosphorus on the mechanical properties of the manufactured foams.

Structure–processing relationships of freeze-cast iron foams fabricated with various solidification rates and post-casting heat treatment

Abstract

Effects of pore morphology on the cyclical oxidation/reduction of iron foams created via camphene-based freeze casting

Solid-oxide iron-air batteries have potential for applications in large-scale energy storage systems, but their storage materials, iron and iron oxides, have limited cycle life due to powder sintering and choking of gas flow. To address this issue, Fe foams are synthesized with either equiaxed or directional dendritic pore structures by camphene-based freeze casting of Fe2O3 powders, followed by H2 reduction to Fe and sintering. For each pore architecture, Fe foams are created with three different initial porosities, ranging from 47 to 63 vol %, and are then cycled at 800 °C under alternating oxidation (via H2O) and reduction (via H2) conditions. The redox-cycled foams are examined by optical microscopy, scanning electron microscopy, and synchrotron X-ray tomography to assess the evolution of their porosity driven by the redox volume changes, sintering, and micropore formation via the Kirkendall effect. After 5 redox cycles, the Fe foams have lost the majority (39 ± 2 vol %) of their initial porosity.

In Vitro Corrosion Behavior of Biodegradable Iron Foams with Polymeric Coating.

Research in the field of biodegradable metallic scaffolds has advanced during the last decades. Resorbable implants based on iron have become an attractive alternative to the temporary devices made of inert metals. Overcoming an insufficient corrosion rate of pure iron, though, still remains a problem. In our work, we have prepared iron foams and coated them with three different concentrations of polyethyleneimine (PEI) to increase their corrosion rates. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used for characterization of the polymer coating. The corrosion behavior of the powder-metallurgically prepared samples was evaluated electrochemically using an anodic polarization method. A 12 weeks long in vitro degradation study in Hanks’ solution at 37 °C was also performed. Surface morphology, corrosion behavior, and degradation rates of the open-cell foams were studied and discussed. The use of PEI coating led to an increase in the corrosion rates of the cellular material. The sample with the highest concentration of PEI film showed the most rapid corrosion in the environment of simulated body fluids.

Thermal properties improvement of lauric acid/iron foam composites with graphene nanoplates as thermal energy storage materials

Abstract Lauric acid (LA)/iron foam composites with graphene nanoplates (GNP) as composite phase change materials (CPCM) were fabricated by melting infiltration. LA was used as a phase change material and iron foams with different pore density (40, 70 and 90 PPI) were used as skeletons. GNP was used as additives to improve thermal conductivity of the CPCM. Fourier transform infrared spectroscopy and X-ray diffraction were used to verify that LA was physically absorbed into iron foam. Scanning electron microscopy was employed to demonstrate that the LA and GNP were well immersed into the iron foam. The thermal properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermal conductivity meter. Impregnating LA with GNP into the metal foam is a novel way to enhance thermal properties of the CPCM. CPCM1 reached a latent heat of 177.82 kJ/kg in the solidifying process. The results of TGA and differential thermogravimetric analysis confirmed that the CPCM maintains good stability. The thermal conductivity of the CPCM has an obvious enhancement. The bigger pore density leads to higher thermal conductivity. The GNP can improve thermal conductivity effectively. Thermal conductivity of CPCM6 reaches 1.227 W/(m K), which is increased by 10.67 times compared to that of lauric acid.

In operando tomography reveals degradation mechanisms in lamellar iron foams during redox cycling at 800 °C

The lifetime of iron-based active materials in high-temperature redox applications (e.g., solid-oxide iron-air batteries, chemical looping) is limited by sintering, accelerated by oxidation/reduction volume changes. Here, in operando X-ray microtomography is used to reveal the evolution of structure, porosity, and extent of reaction in freeze-cast, lamellar iron foams during five redox cycles between Fe and FeO/Fe3O4 (via H2 and H2O) at 800 °C. Foam porosity decreases during oxidations but only partially recovers during reductions, with a net decrease from 77 to 52%. A gas-blocking surface layer, or shell, forms around the foam exterior. By correlating SEM microanalysis with in operando data, the Kirkendall effect is identified as the primary mechanism underlying these degradations. These insights suggest that material lifetime can be improved by measures that prevent the Kirkendall effect, such as combining iron with elements (in solid solution or as a second, redox-inactive phase) that lessen the imbalance of diffusional fluxes.

Evaluation of mechanical properties and hemocompatibility of open cell iron foams with polyethylene glycol coating

The increasing demand for improved implant biomaterials encourages their design and development. Degradable biomaterials have gained considerable attention especially in the past few decades. Metallic biomaterials are commonly applied in current medical practice to replace or repair diseased tissue. Structural materials with appropriate mechanical properties are required for load-bearing orthopedic applications. Moreover, biomaterials must fulfil the safety requirements and exhibit reasonable degradation rates to support the failing tissue and allow a gradual load transfer to the healing bone. Metal foams with open cell structure allow the transport of body fluids, growth of new tissues, improvement of degradation rate and reduction of the stress shielding phenomenon. In this work, iron open cell foams were fabricated by means of powder metallurgy processes. The hemocompatibility and mechanical properties of the porous iron materials without and with polyethylene glycol (PEG) coating were evaluated depending on the time of immersion in a simulated body fluid. It has been discovered, that PEG layer has increased the density and strength of iron foams. A mechanism of corrosion of iron foams with PEG coating layer was proposed. The suppression of hemolysis extension, platelet adhesion, and thrombus formation due to the polymer layer was observed as a result.