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Open-cell macroporous Fe, Cr and their alloys were prepared by dealloying with a metallic melt. By immersing (Fe, Cr)30Ni70 precursors in a Mg melt, Ni selectively dissolved into the Mg and the remaining components formed a bicontinuous structure. Analyses of the thermal coarsening in the melt reveal that evolution of the porous structure is controlled by interfacial diffusion between the melt and precursor solid. The underlying mechanism for the nanoporous structure formation is therefore the same as that in aqueous solution. [Copyright &y& Elsevier]

High-entropy nanomaterials possessing high accessible surface areas have demonstrated outstanding catalytic performance, beating that found for noble metals. In this communication, we report about the synthesis of a new, nanoporous, high-entropy alloy (HEA) possessing open porosity. The nanoporous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%) was fabricated from a precursor (TaMoNbV)25Ni75 alloy (at%) by liquid metal dealloying using liquid magnesium (Mg). Directly after dealloying, the bicontinuous nanocomposite consisting of a Mg-rich phase and a phase with a bulk-centered cubic (bcc) structure was formed. The Mg-rich phase was removed with a 3M aqueous solution of nitric acid to obtain the open, porous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%). The ligament size of this nanoporous HEA is about 69 ± 9 nm, indicating the high surface area in this material. [ABSTRACT FROM AUTHOR]

Surface functionalization is an effective approach to change the surface properties of a material to achieve a specific goal such as improving the biocompatibility of the material. Here, the surface of the commercial biomedical Ti-6Al-7Nb alloy was functionalized through synthesizing of a porous surface layer by liquid metal dealloying (LMD). During LMD, the Ti-6Al-7Nb alloy is immersed in liquid magnesium (Mg) and both materials react with each other. Particularly, aluminum (Al) is selectively dissolved from the Ti-6Al-7Nb alloy into liquid Mg while titanium (Ti) and niobium (Nb) diffuse along the metal/liquid interface to form a porous structure. We demonstrate that the porous surface layer in the Ti-6Al-7Nb alloy can be successfully tailored by LMD. Furthermore, the concentration of harmful Al in this porous layer is reduced by about 48% (from 5.62 ± 0.11 wt.% to 2.95 ± 0.05 wt.%) after 30 min of dealloying at 1150 K. The properties of the porous layer (e.g., layer thickness) can be tuned by varying the dealloying conditions. In-vitro tests suggest improved bone formation on the functionalized porous surface of the Ti-6Al-7Nb alloy. [ABSTRACT FROM AUTHOR]

A hierarchical porous metal has been prepared by two-step liquid metal dealloying using an alloy precursor containing two soluble components and two metal baths. After the first dealloying step, one of the soluble components is dissolved and a coarse porous structure is formed. After a shorter dealloying step in another melt, the other soluble component is dissolved and a fine porous structure is formed within the previously formed coarse ligaments. The resultant porous metal presents a hierarchical morphology with a bimodal pore distribution, resulting in a higher porosity and surface-area-to-volume ratio than what can be formed by one-step dealloying methods. [ABSTRACT FROM AUTHOR]

The solid dealloying reaction was investigated using (Fe,Cr)-Ni and Mg diffusion couples. Ni selectively reacted with Mg and the remaining Fe and Cr formed various topologies. An etching treatment provided interconnected Fe–Cr alloy with a ligament width below 200 nm, which is about one order of magnitude finer than that obtained for dealloying with Mg melt. The formation of ordered single-crystal nanofilaments at the dealloying front suggests that the topology evolved via the recently proposed interfacial spinodal decomposition and diffusion-coupled growth mechanism. [ABSTRACT FROM AUTHOR]

Silicon is a promising material for negative electrode in Li-ion batteries because of high gravimetric capacity. A Si nanomaterial that can accommodate volume expansion accompanied by lithiation is needed for practical application in Li-ion batteries. We prepare three-dimensional nanoporous interconnected silicon material with controlled pore and ligament sizes by dealloying using an Mg–Si precursor and Bi melt. The Mg atoms in the precursor selectively dissolve into Bi, and the remaining Si atoms self-organize into a nanoporous structure with characteristic length ranging from several ten to hundred nanometer. The Li-ion battery electrodes made from nanoporous silicon exhibit higher capacities, increased cycle lives, and improved rate performances compared with those made from commercial Si nanoparticles. Measurements on the electrical resistivity and electrode thickness change by lithiation/delithiation suggest that the superior performance of nanoporous Si electrode originates from the following: (1) The nanoporous Si has much lower electrical resistivity compared with that of the nanoparticle Si owing to the n-type dopant incorporated during dealloying. (2) The nanoporous Si-based electrode has higher porosity owing to the presence of intra-particle pores, which can accommodate Si expansion up to higher levels of lithiation. [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a promising technique to elaborate porous metallic materials with potential applications for catalysis and energy storage. It consists in the selective dissolution of an element out of a precursor alloy by immersing it in a liquid bath. To model this process, we introduce a one-dimensional diffusion model that relies on the thermodynamic properties of the ternary system, and on a maximum velocity criterion of the reaction front. The model is compared to experimental measurements conducted on NiCu samples dealloyed in liquid Ag. Regarding the kinetics, the model enables to reach experimental time-scales, replicate experimental trends, and reveal the influence of the ligament structure on the dealloying rate. Also, by assuming thermodynamic equilibria between solid and liquid phases in the dealloyed region, the microstructure gradient obtained numerically is in satisfactory agreement with experimental measurements. These numerical results are obtained without adjustable parameters, which opens the possibility to predict dealloyed microstructures as function of the process parameters (precursor and bath composition, dealloying time and temperature, etc.). [Display omitted] [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a promising technique for synthesizing non-noble porous materials by preventing oxidation in a metallic melt. This method considers the heats of mixing between precursor elements and a melt element to design miscible and immiscible elements for a precursor. In this study, Ni and Co were selected as the miscible elements in an Mg melt as constituents of (FeCo) 100− x Ni x precursor alloys to understand the complex mechanisms of their dissolution behavior. Dissolution of the second miscible element, Co, was governed by the composition of the Mg melt, because the characteristics of the melt changed in the presence of a high amount of dissolved Ni and its convection. The synthesized FeCo ligaments showed morphology variations depending on the dealloying temperature: the ligaments become more elongated along the dealloying direction at higher temperatures. A double-gyroid-like porous structure with a narrow liquid channel, produced from the (FeCo) 70 Ni 30 precursor, exhibited the highest specific surface area at all processing temperatures from 600 °C to 800 °C. This structure differed completely from that of the typical porous Fe 80 Cr 20 alloy produced under the same liquid metal dealloying conditions. Elongation resulted from time-dependent directional coarsening behavior that was affected by the composition of the Mg melt. Unlabelled Image • First demonstration of 3D interconnected porous FeCo materials produced by liquid metal dealloying • Ligament morphology depends on ordering and coarsening mechanisms at different temperatures. • Strong interaction between FeCo ligaments and the Mg melt affected coarsening behavior. • Double-gyroid-like structure showed the highest specific surface area. • Prerequisite conditions for dissolution of the second miscible element are identified. [ABSTRACT FROM AUTHOR]

Abstract Liquids metal dealloying is a new technology to create porous materials. In this study, a commercial Incoloy 825 nickel superalloy is dealloyed for 1 h at 3 different temperatures to elaborate a fully porous FeCr-based metal with 3 different porous microstructures. The resulting porous metals showed unimodal pore distribution, hierarchical structure or, contain large ligaments inclusions. The passivation ability of the porous material was conformed irrespective of the microstructure. This letter proves the possibility of fabricating low cost high specific surface materials for electrochemical applications. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Liquid metal dealloying is a promising technique to get nanoporous materials which are attractive for their excellent functional properties. From a (FeCr) x -Ni 1−x precursor, it is possible to get porous FeCr with this technique. While immersing precursors in a molten Mg bath, Ni atoms selectively migrate into the Mg bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of FeCr and Mg (with Ni in solid solution). A final etching step removes the Mg solid-state solution phase. Precursors with different compositions were dealloyed and imaged in 3D. From X-ray tomography images, porous FeCr characteristics as solid fraction, phase size, specific surface were extracted. EBSD maps were acquired on samples before and after dealloying. We will show that precursor composition is a key parameter to control pores and grains size while dealloying parameters (time and temperature) are key parameters to control ligaments size and in fine specific surface. By controlling precursor composition and dealloying parameters it is now possible to get dealloyed nanoporous metals with desired grain and porous microstructure by liquid metal dealloying. Highlights • FeCr-Ni precursors were dealloyed in a Mg bath to give FeCr-Mg bicontinuous structure. • FeCr-Mg bicontinuous structure was immersed in HNO 3 solution to get porous FeCr. • (FeCr) x -Ni 1−x precursors are fully FCC phase while porous FeCr are fully BCC phase. • Composition & dealloying parameters are key parameters for controlling microstructure [ABSTRACT FROM AUTHOR]

To obtain anisotropic nanoporous NiCr , some NiCr-Ag composites were prepared using a liquid metal dealloying method and were cold rolled before etching. While immersing (Ni 90 Cr 10 ) 60 Cu 40 precursors in a molten Ag bath, Cu atoms selectively migrate into the Ag bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of NiCr and A g (with Cu in solid solution). These ingots are strong enough to be cold rolled in one or two (perpendicular) directions with a thickness reduction of 70%. A final etching step removes the A g solid-state solution phase. The influence of cold rolling on the microstructure was investigated using X-ray tomography and on the mechanical properties using nanoindentation. We will show how introducing anisotropy into the microstructure and in the mechanical properties was successful while being able to preserve the porous state. [ABSTRACT FROM AUTHOR]

To increase the surface area while decreasing the ligament size of an Nb anode pellet for use as a capacitor, we added Ce to an Mg melt; the dealloying reaction occurred at temperatures lower than 1023 K, the previously lowest recorded temperature for such a reaction. By analyzing the dealloying kinetics, we found the optimum dealloying conditions to produce a minimum ligament size of 100 nm in the Mg 95.7 Ce 4.3 melt: 923 K for 420 s. Using these conditions, we increased the specific surface area of the Nb anode pellet to 4.3 m 2 /g, which increased its mass-specific capacitance to 875,000 μFV/g. [ABSTRACT FROM AUTHOR]

The transition behavior from a Nb–Ni precursor to porous Nb and the coarsening of ligaments by a dealloying reaction in a Mg melt are investigated. Based on these results, the kinetics of the reaction are discussed. When a Nb 25 Ni 75 (at.%) disk was immersed in a Mg melt, the Ni content decreased the most at the surface of the disk and less so towards the interior of the disk. In this disk, it was found that transition layers of body-centered cubic-Nb and Ni 6 Nb 7 formed. These transition layers grew, following a parabolic law, and the activation energy of such growth was close to values reported for the diffusion of solute atoms in liquids, suggesting that diffusion of Ni in the Mg melt was the rate-controlling process of the dealloying reaction. The ligament size depended on time and temperature, following a power law with an exponent of 4, suggesting that surface diffusion was a key part of coarsening. These results agree well with those reported for conventional dealloying in an aqueous solution. Based on the kinetics analyses, the dealloying conditions were optimized to maximize the specific surface area, allowing a Nb electrolytic capacitor to be produced with a maximum mass-specific capacitance of 650,000 μFV g −1 , about three times larger than the highest value previously reported. [ABSTRACT FROM AUTHOR]

Abstract: Porous Nb was prepared by dealloying in a metallic melt. A Ni–Nb precursor was immersed in a Mg melt, and Ni was selectively dissolved into the melt. The remaining Nb self-organized into a bicontinuous structure. Removing the Mg solvent in aqueous HNO3 yielded open-cell sub-μm porous Nb, which was applied in solid electrolytic capacitors after anodization. Ligament size decreased with decreasing immersion time. This increased the mass-specific capacitance to 500,000μFV/g, by increasing the specific surface area to 3.92m2/g. [Copyright &y& Elsevier]

Abstract: A Mg3Cu3Gd bulk metallic glass matrix composite with porous α-Ti dispersoids was prepared by dealloying in a metallic melt. The in situ formed α-Ti dispersoids had a pore-size of ∼500nm, which was imparted from the Ti2Cu precipitate in the prealloy. Pore size was therefore controllable through the cooling rate of the prealloy preparation. Plasticity was not improved apparently, however the maximum fracture stress under four point bending mode increased from 217MPa for the monolithic counterpart to 387MPa. This was due to the optimal relationship where dispersoid size (L)≈dispersoid interval distance (S)≈process zone size (R p ). This was achieved locally within and around the porous Ti dispersoids, and helped improve the toughness and ductility. [Copyright &y& Elsevier]

Dealloying in metallic melts has been used to prepare pure base metals with an open-cell porous structure, an example of which is Ti. In this study, previously suggested strategies have been extended to prepare a porous multicomponent Ti alloy of non-equilibrium body-centered cubic phase at room temperature. Dealloying in metallic melts is a promising method for preparing functional nano- to submicro-porous alloys which cannot be prepared by conventional methods. [ABSTRACT FROM AUTHOR]

Low modulus biomaterials are in focus as potential candidates for biomedical implants ensuring a fast healing of hard tissues. The close match between elastic properties of an implant material and bone are critical to eliminate stress-shielding effect. In this study, we synthesized a low modulus interpenetrating-phase composite of Ti and Mg by liquid metal dealloying. Its Young's modulus value is in the range of that found for human bone which allows for biomedical applications of this material. Unexpectedly, the Young's modulus value of the composite (17.6 GPa) is several times lower than that of each individual constituent phases, namely, Mg (45 GPa) and Ti (110 GPa). Using micromechanical modelling, it is demonstrated that the origin of the anomalously low modulus can be related to a weakened interface between the constituents. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Microporous ferritic stainless steel was produced from Incoloy 800 via LMD. • LMD can be used industrially to produce inexpensive porous materials. • Minor elements in commercial alloys tend to slow down coarsening kinetics. • Nitric acid that serves for Mg dissolution also induces a passivation treatment. • The pore size (0.5–1.5 μm) has no significant effect on pitting sensitivity. • The pore size plays a role on diffusion processes through the porous structure. Liquid metal dealloying is a newly available technology used to create bulk porous materials. In this study, a commercial nickel-based superalloy, Incoloy 800, was dealloyed to elaborate a fully porous ferritic stainless steel. The Mg selective dissolution in nitric acid solution acts as a passivation treatment that enhances the passive film resistance. Corrosion tests confirm the beneficial effect of the nitric acid treatment on the Cr enrichment of the passive film thus improved the material resistance. The electrochemical characterizations show a higher effect of the size porosities on the diffusion kinetics of the electrolyte rather than on the pitting sensitivity. [ABSTRACT FROM AUTHOR]