Immiscible Metals Research Articles

Formation of ordered and disordered interfacial films in immiscible metal alloys

Atomistic simulations are used to study segregation-induced intergranular film formation in CuZr and CuNb alloys. While CuZr forms structurally disordered or amorphous films, ordered films comprised of a second phase usually precipitate in CuNb, with a critical nucleation size of ~1nm below which the ordered phase cannot form. While the ordered film is retained at high temperature for a low energy Ʃ11 (113) boundary, a disordering transition is observed for a high energy Σ5 (310) boundary at low dopant concentrations. Finally, the effect of free surfaces on dopant segregation and intergranular film formation is investigated for both alloys.

Kinetic Trapping of Immiscible Metal Atoms into Bimetallic Nanoparticles through Plasmonic Visible Light-Mediated Reduction of a Bimetallic Oxide Precursor: Case Study of Ag–Pt Nanoparticle Synthesis

Alloying of two metals is commonly used to create nanomaterials with unique physical and chemical properties. The ability to synthesize well-mixed bimetallic alloy nanoparticles, however, is often limited by the intrinsic immiscibility of metals. To overcome this issue, extreme synthesis conditions, using high energy γ radiation or very high temperatures, have been employed to trap metal atoms of immiscible metals in well-mixed alloy nanostructures. Herein, we demonstrate a more benign synthesis strategy for creating well-mixed bimetallic nanoparticles of immiscible metals. We demonstrate a formation of Ag–Pt bimetallic nanoparticles through the visible-light mediated reduction of a hollow bimetallic oxide precursor containing Ag and Pt oxide. We exploit the optical properties of Ag by using visible light to excite surface plasmon resonance to drive the reduction of the Pt oxide thereby destabilizing the bimetallic precursor. Under the influence of resonant light the hollow bimetallic precursor restructur...

Coalescence of Immiscible Liquid Metal Drop on Graphene.

Molecular dynamics simulations were performed to investigate the wetting and coalescence of liquid Al and Pb drops on four carbon-based substrates. We highlight the importance of the microstructure and surface topography of substrates in the coalescence process. Our results show that the effect of substrate on coalescence is achieved by changing the wettability of the Pb metal. Additionally, we determine the critical distance between nonadjacent Al and Pb films required for coalescence. These findings improve our understanding of the coalescence of immiscible liquid metals at the atomistic level.

An early geodynamo driven by exsolution of mantle components from Earth's core.

Terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate mantle to the metallic core1–3, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth’s major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations4. Using core formation models5, we further show that a high-temperature event during Earth’s accretion (such as the Moon-forming giant impact6) can contribute significant amounts of magnesium to the early core. As it subsequently cools, the ensuing exsolution7 of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification8 — the primary driver of the Earth’s current magnetic field9–11. Since the inner core is too young12 to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation13 of an ancient field at least 3.45 Gyr old.

Influence of high-energy ball milling on electrical resistance of Cu and Cu/Cr nanocomposite materials produced by Spark Plasma Sintering

A combination of High Energy Ball Milling in the planetary mills (HEBM) with Spark Plasma Sintering (SPS) allows production of dense (>97%) nano-composites of immiscible metals, Cu and Cr, so-called pseudo-alloys. New results on electrical resistance of the pseudo-alloys have been obtained from cryogenic to elevated temperatures, in comparison with the Cu-Cr micro-composites and pure Cu. The results show that duration of HEBM influences hardness and electric resistivity of the materials in a wide temperature range, including cryogenic residual resistivity. This influence remains after SPS. Increasing of the electrical resistivity and hardness with increasing of the mechanical impact is explained by significant increase of specific surface of grain boundaries due to grains refinement. At the same time, some regimes of HEBM results in increasing of the electrical conductivity (decreasing resistance) due to mechanical boundaries purification. These findings allow optimization of the process for preparation of the alloys with desired electrical conductivity and mechanical properties, specifically for application as electrode materials.

Experimental simulation of fragmentation and stratification of core debris on the core catcher of a fast breeder reactor

The complex and coupled phenomena of two simultaneous molten metal jets fragmenting inside a quiescent liquid pool and settling on a collector plate are experimentally analysed in the context of safety analysis of a fast breeder reactor (FBR) in the post accident heat removal phase. Following a hypothetical core melt down accident in a FBR, a major portion of molten nuclear fuel and clad/structural material which are collectively termed as ‘corium’ undergoes fragmentation in the bulk coolant sodium in the lower plenum of the reactor main vessel and settles on the core catcher plate. The coolability of this decay heat generating debris bed is dependent on the particle size distribution and its layering i.e., stratification.Experiments have been conducted with two immiscible molten metals of different densities poured inside a coolant medium to understand their fragmentation behaviour and to assess the possibility of formation of a stratified debris bed. Molten aluminium and lead have been used as simulants in place of molten stainless steel and nuclear fuel to facilitate easy handling. This paper summarizes the major findings from these experiments. The fragmentation of the two molten metals are explained in the light of relevant dimensionless numbers such as Reynolds number and Weber Number. The mass median diameter of the fragmented debris is predicted from nonlinear stability analysis of slender jets for lead jet and using Rayleigh's classical theory of jet breakup for aluminium jet. The agreement of the predicted values with the experimental results is good. These experiments indicate that complete segregation of the lighter component above the denser component does not happen. However, there is segregation observed in the radial direction to a certain extent in the case of rib-partitioned collector plate pointing to the significance of the geometry of the collector plate in settling and segregation aspects. It is observed that fragmentation phenomenon with its interplaying governing forces, interferes with the settling aspects and seems to suppress stratification that arises due to density differences between the molten melts. Moreover, the thermophysical properties of the metals play a crucial role in the fragmentation and settling behaviour as exemplified by the relevant dimensionless numbers.

ChemInform Abstract: Solid‐Solution Alloying of Immiscible Metals at the Nanoscale: Ir and Au.

AbstractNanoscale solid solutions of Ir and Au over a wide compositional range and a layer thickness of 80 nm are obtained by electrochemical deposition using a 90 nm sputtered Au film on a Si wafer substrate as working electrode in an aqueous electrolyte containing IrCl3 (25 μM) and HAuCl4 (12.5 μM) at 323 K.

Coalescence behavior of liquid immiscible metal drops in two-wall confinement.

Molecular dynamics (MD) simulations are performed to investigate the coalescence of the liquid Al and Pb drops in the graphene (G) walls and pillared-graphene (PG) walls. The confining walls can affect the coalescence dynamics of two adjacent films by restricting the movement of one of the metal drops; however, the coalescence behavior is different in the G-walls and the PG-walls. Two un-contacted films can still merge into one bigger drop because of the restricting effect of the walls, in which the movement of the Pb drop plays a predominant role. The coalescence time decreases with the decrease of the confining space. Our findings demonstrate that the coalescence dynamics can be controlled by tuning the confining space or wall surface.

Solid-solution alloying of immiscible metals at the nanoscale: Ir and Au

A solid solution alloy of Ir–Au, theoretically predicted to be an excellent catalyst, equivalent to Pt, has been experimentally synthesized.

Synthesis of new metastable nanoalloys of immiscible metals with a pulse laser technique

The generation of nanoalloys of immiscible metals is still a challenge using conventional methods. However, because these materials are currently attracting much attention, alternative methods are needed. In this article, we demonstrate a simple but powerful strategy for the generation of a new metastable alloy of immiscible metals. Au1−xNix 3D structures with 56 at% of nickel in gold were successfully manufactured by the pulsed laser irradiation of colloidal nanoparticles. This technology can be used for preparing different metastable alloys of immiscible metals. We hypothesise that this technique leads to the formation of alloy particles through the agglomerations of nanoparticles, very fast heating, and fast cooling/solidification. Thus, we expect that our approach will be applicable to a wide range of inorganic solids, yielding even new metastable solids that fail to be stable in the bulk systems, and therefore do not exist in Nature.

A nanoglass alloying immiscible Fe and Cu at the nanoscale.

Synthesized from ultrafine particles with a bottom-up approach, nanoglasses are of particular importance in pursuing unique properties. Here, we design a metallic nanoglass alloy from two components of ∼Cu64Sc36 and ∼Fe90Sc10 nanoglasses. With nanoalloying mutually immiscible Fe and Cu, the properties of the nanoglass alloys can be tuned by varying the proportions of the ∼Fe90Sc10 component. This offers opportunity to create novel metallic glass nanocomposites and sheds light on building a structure-property correlation for the nanoglass alloys.

Nano-Crystal Formation and Growth from High-Fluence Ion Implantation of Au, Ag or Cu in Silica

The linear and non-linear optical properties of silica may be tailored by the introduction of a random distribution of nanocrystallites of an immiscible metal within a near-surface region. The size, size distribution, and spatial distribution of these crystallites must be controllable in order to optimize the functional properties for device applications. In this paper, we present a novel fabrication technique that offers such control. Energetic metal ions are implanted in silica at room temperature. Subsequent heat treatment leads to diffusion of the implanted atoms, nucleation and growth of metal crystallites, and Ostwald ripening of the resulting clusters. We have observed the kinetics and effective activation energies describing the multiple processes involved, for the cases of Au, Ag or Cu implanted at MeV energies, at various fluences, and then annealed at fixed temperatures in the range 500°C-1000°C. Effective activation energies found for nanocrystal nucleation and growth at temperatures below 800°C (e.g. 64 meV for Ag) are replaced above this temperature range by much higher activation energies (e.g. 400 meV for Ag). We may attribute this to the depletion of un-attached mobile metal atoms (so that ripening of clusters will be limited by energy barriers for escape of such mobile atoms from small crystallites), and/or the annealing of implant-caused stress in the silica structure at high temperatures, that creates new channels for thermal diffusion of metal atoms within the silica host.

Microwave synthesis of classically immiscible rhodium-silver and rhodium-gold alloy nanoparticles: highly active hydrogenation catalysts.

Noble metal alloys are important in large-scale catalytic processes. Alloying facilitates fine-tuning of catalytic properties via synergistic interactions between metals. It also allows for dilution of scarce and expensive metals using comparatively earth-abundant metals. RhAg and RhAu are classically considered to be immiscible metals. We show here that stable RhM (M = Ag, Au) nanoparticles with randomly alloyed structures and broadly tunable Rh:M ratios can be prepared using a microwave-assisted method. The alloyed nanostructures with optimized Rh:M compositions are significantly more active as hydrogenation catalysts than Rh itself: Rh is more dilute and more reactive when alloyed with Ag or Au, even though the latter are both catalytically inactive for hydrogenation. Theoretical modeling predicts that the observed catalytic enhancement is due to few-atom surface ensemble effects in which the overall reaction energy profile for alkene hydrogenation is optimized due to Rh-M d-band intermixing.

Bulk Cu–Cr nanocomposites by high-energy ball milling and spark plasma sintering

A set of nanocomposite Cu–Cr powders with the grain size of these immiscible metals below 5nm were prepared by high-energy ball milling. The powders were then consolidated by short-term (5min) spark plasma sintering at 700–900°C under pressure (50MPa) to obtain essentially pore-free pseudo-alloys. The grain sizes in the produced bulk materials remained within the ranges 5–60nm for Cr-based phase and 200–300nm for Cu-based matrix. These nanocomposites have a Vickers microhardness up to 3.9GPa and a specific electrical resistivity in the range 6–9.6μΩcm, which make them promising candidates for the application in high-voltage circuit breakers.

An ordered nanomaterial from bulk processing

<xhtml:span xmlns:xhtml="http://www.w3.org/1999/xhtml" xml:lang="en">When two immiscible metal sheets are squeezed, cut, and stacked together repeatedly, a remarkably ordered nanoscale structure can emerge at the interfaces between them.</xhtml:span>

Exotic Alloys Obtained by Condensation of Metallic Vapors

New methods of producing small quantities of exotic alloys from immiscible metals (and elements in general) are described with two examples: An alloy of aluminium with silver and one of aluminium with tungsten. There is no limit to the number of components that can form special alloys by this method and their applications can be foreseen to be quite useful in the future.

Surface morphology and interface chemistry under ion irradiation – Simultaneous atomistic simulation of collisional and thermal kinetics

A novel program package has been developed which allows for the simultaneous treatment of atomistic kinetics in collision cascades caused by energetic ion impacts and thermally activated relaxation and diffusion. In this 3D program named TRIDER (TRansport of Ions in matter with DEfect Relaxation) the collision cascades treated in the framework of the Binary Collision Approximation has been combined with kinetic lattice Monte-Carlo simulations of the atomistic relaxation and diffusion. TRIDER simulations allow a more realistic description of ion-induced surface patterning because subsurface defect kinetics can be included in the simulations, which is demonstrated for low-energy Ar+ ion irradiation of silicon. A deeper understanding of ion beam mixing of bimetal interfaces can also be achieved: it is shown that the conventional Gaussian mixing profile is changed substantially for immiscible metals due to precipitation and for chemically active metals due to formation of intermetallics of different stoichiometry.

A chemical approach toward low temperature alloying of immiscible iron and molybdenum metals

The present research is based on a low temperature operated feasible method for the synthesis of immiscible iron and molybdenum metals’ nanoalloy for technological applications. The nanoalloy has been synthesized by pyrolysis of homogeneous powder precipitated, from a common solvent, of the two complexes, trisbipyridineiron(II)chloride, [Fe(bipy)3]Cl2, and bipyridinemolybedenum(IV) chloride, [Mo(bipy)Cl4], followed by heating at 500°C in an inert atmosphere of flowing argon gas. The resulting nanoalloy has been characterized by using EDXRF, AFM, XRD, magnetometery, 57Fe Mössbauer and impedance spectroscopies. These results showed that under provided experimental conditions iron and molybdenum metals, with known miscibility barrier, alloy together to give (1:1) single phase material having particle size in the range of 48–66nm. The magnetism of iron is considerably reduced after alloy formation and shows its trend toward superparamagnetism. The designed chemical synthetic procedure is equally feasible for the fabrication of other immiscible metals.

Development of arrayed nanoporous Ag/W films by alternate deposition

Metals with well ordered porous networks exhibit interesting electronics, photonics and antimicrobial properties, but fabrication of ordered porous metal by sputtering deposition is difficult. A new method to develop arrayed nanoporous multilayered films in the Ag/W system has been reported in this work. The results show that the structure of the multilayers is dependent on the periodicity. Multilayers with periodicity not larger than 30 nm have an arrayed porous structure. The formation of the porous structure can be ascribed to the initial Volmer–Weber growth due to the large positive enthalpy of mixing Ag and W and the following shadowing effect during alternate sputtering deposition. This method gives a controllable way to fabricate nanoporous binary immiscible metal films.

Structural and magnetic investigations on metastable Ag–Fe nanophase alloy

Nanocrystalline Ag–Fe alloy samples of various compositions were synthesized by chemical reduction method using sodium borohydride as the reducing agent. The structure analysis of the as prepared and the annealed samples were carried out. The fcc structure of the as prepared samples was stable up to 400°C. As bulk Ag and Fe are immiscible metals, nanophase alloy formation of these two metals was studied from the broad exothermic peak observed and the enthalpy changes were calculated from the differential scanning calorimetric analysis. The presence of Ag and Fe in their metallic form was verified by performing X-ray photoelectron microscopy studies. The microstructure of these samples reveals that the particles are nanosized. The results of the magnetic characterization of the as synthesized and annealed Ag50Fe50 sample and the conclusions drawn there from are in correlation with the metastable nature of the samples up to 400°C and the phase changes in the sample annealed at 500°C.