Metallic Solid Solutions Research Articles

Highly Active Cerium Oxide Supported Solution Combustion Cu/Mn Catalysts for CO-PrOx in a Hydrogen-Rich Stream

Mono- and di-substituted cerium oxide catalysts, viz. Ce0.95Cu0.05O2-δ, Ce0.90Cu0.10O2-δ, Ce0.90 Cu0.05Mn0.05O2-δ, Ce0.85Cu0.10Mn0.05O2-δ, and Ce0.80Cu0.10Mn0.10O2-δ, were synthesized via a one-step urea-assisted solution combustion method. The elemental composition and textural and structural properties of the catalysts were determined by various physical, electronic, and chemical characterization techniques. Hydrogen temperature-programmed reduction showed that co-doping of copper and manganese ions into the CeO2-δ lattice improved the reducibility of copper. Powder XRD, XPS, HR-TEM, and Raman spectroscopy showed that the catalysts were a singled-phased, solid-solution metal oxide with a cerium oxide cubic fluorite (cerianite) structure, and evidence of oxygen vacancies was observed. Catalytic results in the preferential oxidation of CO in a hydrogen-rich stream showed that complete CO conversion occurred between 150 and 180 °C. Furthermore, at 150 °C, Ce0.90Cu0.05Mn0.05O2-δ, Ce0.90 Cu0.10O2-δ, and Ce0.85Cu0.10Mn0.05O2-δ catalysts were the most active, achieving complete CO conversion and CO2 selectivity of 81, 79, and 71%, respectively. The catalysts performed moderately in the presence of CO2 and water, with the Ce0.90Cu0.05Mn0.05O2-δ catalyst giving a CO conversion of 80% in CO2, which decreased to about 60% when water was added.

Electron Concept of Hydrogen Embrittlement and Hydrogen-Increased Plasticity of Metals

Based on theoretical and experimental studies of hydrogen effect on the electron structure of iron, nickel and titanium, an electron concept is proposed for hydrogen embrittlement as well as for hydrogen-improved plasticity of engineering metallic materials. This concept implies a hydrogen-caused redistribution of valence electrons across their energy levels and an increase in the density of electron states at the Fermi level, causing a softening of the crystal lattice and, thereby, leading to a decrease in the specific energy of dislocations with consequent increase in their mobility. Innate phenomena in metallic solid solutions, namely, short-range atomic order in its two versions, short-range ordering and decomposition, are shown to be a precondition for the localization of plastic deformation. Hydrogen enhances merely this effect resulting in pseudo-brittle fracture. The role of hydrogen-induced superabundant vacancies in hydrogen-caused localization of plastic deformation and grain-boundary fracture in pure metals is discussed. Using the temperature- and strain-dependent internal friction, the enthalpies of hydrogen diffusion and hydrogen–dislocation binding are studied, and their controlling effect on the temperature- and strain-rate-dependent hydrogen embrittlement is demonstrated. Finally, a physical rationale is proposed for using hydrogen as a temporary alloying element in the technological processing of titanium alloys, and for a positive hydrogen effect on the fatigue life and plasticity of austenitic steels.

Metal-organic framework-derived carbon-supported high-entropy alloy nanoparticles applied in ammonia borane hydrolytic dehydrogenation

While high-entropy alloy nanoparticle (HEA NP) catalysts from a sacrificial high-entropy-MOF (HE-MOF) have been attractive, their conventional characterizations may be misleading. Here, we report HEA NPs on HE-MOF-derived carbon (HE-MDC) via direct pyrolysis of MnFeCoNiCu HE-MOF in Ar and H2 at different temperatures and durations with a fast-ramping rate. With the profound investigations of the metal NPs on HE-MDCs by synchrotron radiation X-ray diffraction and absorption, we revealed that the Ar-treated HE-MDCs had either Cu-dominant solid solution or phase-segregated metal NPs, whereas H2 pyrolysis yielded well-dispersed HEA NPs on HE-MDCs. For ammonia borane hydrolysis, although the metal NP size in H2-treated HE-MDC was not the smallest, it showed the fastest dehydrogenation rate (TOF=5.76 molH₂∙min−1∙molcat-1), 2 ∼ 4 times faster than the Ar-treated HE-MDCs. It emphasized the crucial role of elemental uniformity in the HEA NPs over the traditionally reported catalyst size.

Synthesis of Ti1‐xWx Solid Solution MAX Phases and Derived MXenes for Sodium‐Ion Battery Anodes

AbstractA distinguishing feature of MAX phases and their MXene derivatives is their remarkable chemical diversity. This diversity, coupled with the 2D nature of MXenes, positions them as outstanding candidates for a wide range of electrochemical applications. Chemical disorder introduced by a solid solution can improve electrochemical behavior. Up to now, adding considerable amount of tungsten (W) in MAX phase and MXenes solid solutions, which can enhance electrochemical performance, proved challenging. In this study, the synthesis of M site Ti1‐xWx solid solution MAX phases are reported. The 211‐type (Ti1‐xWx)2AlC exhibits a disordered solid solution, whereas the 312‐type (Ti1‐xWx)3AlC2 displays a near‐ordered structure, resembling o‐MAX, with W atoms preferentially occupying the outer planes. Solid‐solution MXenes, Ti2.4W0.6C2Tz, and Ti1.6W0.4CTz, are synthesized via selective etching of high‐purity MAX powder precursors containing 20% W. These MXenes are evaluated as sodium‐ion battery anodes, with Ti1.6W0.4CTz showing exceptional capacity, outperforming existing multilayer MXene chemistries. This work not only demonstrates the successful integration of W in meaningful quantities into a double transition metal solid solution MAX phase, but also paves the way for the development of cost‐effective MXenes containing W. Such advancements significantly widen their application spectrum by fine‐tuning their physical, electronic, mechanical, electrochemical, and catalytic properties.

Exploring microstructures of metal-doped oxides via simulated Raman spectrum

Solid solution of metal-doped oxide has been widely used in material industry and catalysis process. Its performance is highly correlated with the distribution of doped ions. Due to the complex distribution of doped ions in solid solution and its variation with temperatures, to obtain the microstructures of metal-doped ions in solid solution remains a substantial challenge. Taken Ce1-xZrxO2 as a model, the global structure searching, structures proportion with temperature determined by Boltzmann distribution, and the weighted simulation Raman spectra were integrated to explore the microstructures of metal-doped solid solution oxides. It was further verified by application into rutile and anatase TiO2 mixture, indicating that the present method is feasible to deduce the microstructure of metal composite oxides. We anticipate that it provides a powerful solution to explore microstructures of solid solution and complex metal oxides.

Concentration effects in multicomponent metallic solid solutions

In the equiatomic approximation, the dependence of the lattice FCC parameter and the Debye temperature from the atomic fate x of the doping element, which is alternately represented by all elements of a multicomponent solid solution, including high-entropy alloys were obtained. The calculations were carried out on the example of a five-component (based on Cu, Ni, Co, Fe, and Al) or six-component (based on Cu, Ni, Co, Fe, and Cr, Ti) metal systems. It was found that by varying x within x = (0 - 0.3), it is possible to obtain a change in the lattice FCC parameter from 0 to 0.03 nm and the Debye temperatures from 0 to 80 K. The proposed new characteristics are integral and differential concentration coefficients, the magnitude and sign of which can predict concentration dependences for the lattice parameter and the Debye temperature.

Hydrogen in metallic alloys ─ embrittlement and enhanced plasticity: a review

Abstract The evolution of ideas concerning the nature of hydrogen embrittlement of engineering metallic materials is described based on a number of the proposed hypotheses and corresponding experiments. The main attention is paid to two of them, namely hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Recent attempts to interconnect the both models as HELP + HEDE and HELP-mediated HEDE ones are also estimated. A conclusion is made that HELP model is preferential for understanding the entire array of experimental data with a caveat that it is necessary to consider the chemical nature of hydrogen atoms and view them not only as point defects. Based on the studies of hydrogen effect on the atomic interactions in iron, nickel, titanium, and its alloys, it is shown that the electron approach to HELP phenomenon adequately describes two competitive features of hydrogen behavior in metals: increased brittleness and enhanced plasticity. Due to the increase in the concentration of free electrons, hydrogen decreases the elasticity moduli, which causes the crystal lattice to soften. For this reason, the formation of hydrogen atmospheres around the dislocations decreases the start stress of dislocation sources, as well as line tension of emitted dislocations, enhancing thereby their mobility, and weakens repulsion between dislocations in their pile-ups. The range of temperatures and strain rates in which hydrogen embrittlement occurs is controlled by the enthalpies of hydrogen atoms’ diffusion and their binding to dislocations. The resulting consequences for mechanical properties depend on the short-range atomic order, SRO, which inherently occurs in the metallic solid solutions and localizes plastic deformation both in the cases of short-range atomic ordering and of short-range atomic decomposition. Hydrogen enhances slip localization because of its different solubility in the submicrovolumes of short-range decomposed solid solutions. If SRO is absent or not remarkably formed, the hydrogen-increased concentration of free electrons results in enhanced plasticity. Available positive hydrogen effects on the plasticity of titanium β-alloys and austenitic steels are presented and interpreted.

Decoration of cyanamide groups to tune the surface electronic structures of semiconductor photocatalysts for efficient solar driven CO2 reduction

The using of reductive cocatalysts to dictate the transfer path of electrons towards targeting products is indispensable for photocatalytic CO2 reduction reaction (CRR). However, the development of low-cost and highly selective cocatalysts for photocatalytic CRR remains a daunting challenge. Herein, a functional molecule decoration strategy is proposed to tune the surface electronic structures of semiconductor photocatalysts, in order to promote their photocatalytic performance in CRR. We employ cyanamide groups as the chemical modifiers to regulate the CRR performance of solid solution metal sulphide photocatalysts. The synthesized photocatalysts exhibit excellent photocatalytic performance in CRR, and the highest CO evolution rate exceeds 1400 μmol g−1h−1, being among the best results reported to date. Multiple characterizations in combination with theoretical simulations further demonstrate that the decorated cyanamides do not act as active sites, but changes the electronic structures of the neighboring surface lattice metal atoms and decreases the kinetic barrier of the rate determining *CO2→*COOH step, thereby making the surface much more active for photocatalytic CRR. These findings explicitly verify the effectiveness of the functional molecule decoration strategy in promoting the CRR performance of photocatalysts, and also open up a new pathway for the development of highly efficient and selective catalysts for specific catalytic reactions.

Synthesis of non-noble metal solid solution (Cd0.76Co0.17Mo0.07S) via MOF precursors for enhanced hydrogen production

Ethy-CCMS with excellent photocatalytic hydrogen production performance was prepared using MOFs as precursors.

Photo-Activated Growth and Metastable Phase Transition in Metallic Solid Solutions.

Laser processing in metals is versatile yet limited by its reliance on phase transformation through heating rather than electronic excitation due to their low absorptivity, attributing from highly ordered structures. Metastable states (i.e., surfaces, glasses, undercooled liquids), however, present a unique platform, both energetically and structurally to enable energy landscape tuning through selective stimuli. Herein, this ansatz is demonstrated by exploiting thin passivating oxides to stabilize an undercooled state, followed by photo-perturbation of the near surface order to induce convective Marangoni flows, edge-coalescence and phase transition into a larger metastable solid bearing asymmetric composition between the near surface and core of the formed structure. The self-terminating nature of the process creates a perfectly contained system which can maintain a high relaxation energy barrier hence deep metastable states for extended periods of time.

Hydrogen adsorption by a porous bimetallic solid solution carbide MAX phases synthesized in an open atmosphere

Multilayer and porosity are significant traits for energy storage materials, especially for hydrogen storage and utilization. However, the material must first undergo subsequent sequential investigation for accurate quantification to be a candidate for hydrogen storage. The mixed metallic MAX phase and their derivatives MXene have the potential to be used for hydrogen storage. In this paper, we describe the formation of low temperature (1100 °C), porous, and high purity (84.92 %) bimetallic solid solution Titanium Vanadium Aluminum Carbide (TiVAlxC) MAX phases in an open atmosphere, where the variation of x, e.g., Al mole content, is critical for obtaining high purity metallic solid solution MAX phases. The BET comparative analysis shows the textural features of the TiVAlxC with change in Al and end phases, i.e., Ti2AlC (Titanium Aluminum Carbide) and (Vanadium Aluminum Carbide) V2AlC. The outcomes are evident that impurity, crystallinity, and crystallite size impact the textural properties of the synthesized MAX phases. Corelative findings on accurate quantification of hydrogen uptake based upon textural properties. The gravimetric hydrogen storage capacity of Ti2AlC, TiVAl1.3C, and V2AlC phases are 0.33, 0.62, and 1.29%wt, respectively. The gravimetric analysis provided valuable insights into the isothermal hydrogen adsorption of TiVAlxC and its end phases, demonstrating these materials' ability to be used for future hydrogen storage.

Investigation into the coking-related key reaction steps in dry reforming of methane over NiMgOx catalyst

With pre-reduced NiMgOx catalyst, the structure evolution, catalytic performance, surface species and coking-related reaction steps are investigated in methane dry reforming (DRM) at selected temperatures. Satisfactory conversion of CH4 and CO2, H2/CO ratio, and anti-coke stability are achieved in long-term (78 h) reaction at 650 °C as a proper temperature. The characterizations evidence co-existence of metallic Ni0 and solid solution phases in the working catalysts. Combined catalytic evaluation and coke analysis reveal that, at 650 °C, endothermic CO2-free CH4 decomposition shows a high initial rate for H2 production but severe coke deposition for rapid deactivation, serving as the primary coking process. In contrast, exothermic CO disproportionation exhibits a lower reaction rate and a higher coke graphitization degree. The in-situ DRIFT spectra demonstrate that carbonates and bicarbonates serve as the primary adsorbates during CO2 dissociation process, whereas formate intermediates dominate in DRM reactions. Such evolution of the surface species verifies facile dissociation of both CH4 and CO2 in well-matched rates, promoting coke-resistance DRM reaction over NiMgOx catalyst.

Ti-Mo-O Nanotube Arrays Grown by Anodization of Magnetron Sputtered Films

In this study, we introduced the method for the growth of titanium molybdenum oxide (TMO) nanotubes directly from metallic precursor solid state solution and provided their structural and chemical characterization. Precursor films with content of molybdenum from 32 to 82 at% were prepared using co-deposition magnetron sputtering. The optimization of deposition parameters allowed for the growth of a continuous nanotube array with a length up to 700 nm ± 10% by anodic oxidation. Scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) revealed nanotube formation with Ti1−xMoxO2 composition, where x can reach the value of 0.5. Scanning transmission electron microscopy combined with EDS (STEM-EDS) confirmed the incorporation of Mo into the TiO2 lattice and uniform elemental distribution across the nanotube at the submicron level. The nanobeam electron diffraction (NBD) and X-ray diffraction analyses (XRD) did not show any notable crystal phase formation for the titanium molybdenum oxide phase.

The Characteristics of Soil Dissolved Organic Carbon and Their Influences on Metal Solid-Solution Partitioning in Subtropics Agricultural Soils

The Characteristics of Soil Dissolved Organic Carbon and Their Influences on Metal Solid-Solution Partitioning in Subtropics Agricultural Soils

Dynamic tracking of exsolved PdPt alloy/perovskite catalyst for efficient lean methane oxidation

Supported Pd based catalysts are considered as the efficient candidates for low-carbon alkane oxidation for their outstanding capability to break C-H bond. Whereas, the irreversible deactivation of Pd based catalysts was still frequently observed. Herein, we reinforced the extruded Pd nanoparticles with quantitive Pt to assemble the evenly distributed PdPt nanoalloy onto ferrite perovskite (PdPt-LCF) matrix with strengthened robustness of metal/oxide support interface. We further co-achieved the enhanced performance, anti-overoxidation as well as resistance of vapor-poisoning in durability measurement. The operando X-ray photoelectron spectroscopy (O-XPS) combined with various morphology characterizations confirms that the accumulation of surface deep-oxidation species of Pd4+ is the culprit for fast activity loss in exsolved Pd system, especially at high temperature of 400 °C. Conversely, it could be completely suppressed by in-situ alloying Pd with equal amount of Pt, which helps maintain the metastable Pd2+/Pd shell and metallic solid-solution core structure. The density function theory (DFT) calculations further buttress that the dissociation of CH was facilitated on alloy/perovskite interface which is, on the contrary, resistant toward O–H bond cleavage, as compared to Pd/perovskite. Our work suggests that the modification of exsolved metal/oxide catalytic interface could further enrich the toolkit of heterogeneous catalyst design.

Metastable Solid Solutions Formed by Metal Nanoparticles

Metastable solid solutions of metals have been obtained using nano- and subnanoparticles. This study shows the effect of the size of atoms of a second element on the multiple increase in solubility and limiting concentration in the solvent, independently of the type of crystal lattice. As an example, the limiting solubility of lead (rPb = 0.935 nm) in niobium (rNb = 0.625 nm) is 23.0 at % and that of cadmium (rCd = 0.1727 nm)in niobium is 64.0 at %. Further, amorphization of the matrix metal occurs. Compared to metastable solid solutions with the equilibrium systems for which the Hume–Rothery rules work, alloys are formed from metals with different types of crystal lattices. In many cases, a 15% limit of the difference of the sizes of metal atoms is observed. There is a strong discrepancy in the valences of atoms and, in rare cases, in electronegativity. Using analysis of the attributes of the alloys prepared by sputtering of ultradisperse particles, the possibility of expanding the boundaries of the Hume–Rothery criteria should be noted for metastable alloys, in comparison to their equilibrium analogs, which indicates the possibility of deviation from the traditional forecasting the routine of preparation of the material.

Graph neural networks predict energetic and mechanical properties for models of solid solution metal alloy phases

We developed a PyTorch-based architecture called HydraGNN that implements graph convolutional neural networks (GCNNs) to predict the formation energy and the bulk modulus for models of solid solution alloys for various atomic crystal structures and relaxed volumes. We trained the GCNN surrogate model on a dataset for nickel–niobium (NiNb) generated by the embedded atom model (EAM) empirical interatomic potential for demonstration purposes. The dataset was generated by calculating the formation energy and the bulk modulus as a prototypical elastic property for optimized geometries starting from initial body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal compact packed (HCP) crystal structures, with configurations spanning the possible compositional range for each of the three types of initial crystal structures. Numerical results show that the GCNN model effectively predicts both the formation energy and the bulk modulus as function of the optimized crystal structure, relaxed volume, and configurational entropy of the model structures for solid solution alloys.

Enhanced membraneless fuel cells by electrooxidation of ethylene glycol with a nanostructured cobalt metal catalyst

The advancement of effective and long-lasting electrocatalysts for energy storage devices is crucial to reduce the impact of the energy crisis. In this study, a two-stage reduction process was used to synthesize carbon-supported cobalt alloy nanocatalysts with varying atomic ratios of cobalt, nickel and iron. The formed alloy nanocatalysts were investigated using energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy to determine their physicochemical characterization. According to XRD results, Cobalt-based alloy nanocatalysts form a face-centered cubic solid solution pattern, illustrating thoroughly mixed ternary metal solid solutions. Transmission electron micrographs also demonstrated that samples of carbon-based cobalt alloys displayed homogeneous dispersion at particle sizes ranging from 18 to 37 nm. Measurements of cyclic voltammetry, linear sweep voltammetry, and chronoamperometry revealed that iron alloy samples exhibited much greater electrochemical activity than non-iron alloy samples. The alloy nanocatalysts were evaluated as anodes for the electrooxidation of ethylene glycol in a single membraneless fuel cell to assess their robustness and efficiency at ambient temperature. Remarkably, in line with the results of cyclic voltammetry and chronoamperometry, the single-cell test showed that the ternary anode works better than its counterparts. The significantly higher electrochemical activity was observed for alloy nanocatalysts containing iron than for non-iron alloy catalysts. Iron stimulates nickel sites to oxidize cobalt to cobalt oxyhydroxides at lower over-potentials, which contributes to the improved performance of ternary alloy catalysts containing iron.

Modifying Copper with Alumina during a Mechanically Stimulated Reaction

IR spectroscopy, electron microscopy, and X-ray diffraction analysis, including the application of synchrotron radiation, have been used to study the mechanochemical reduction of copper oxide with alumi-num at the stoichiometric ratio of the components and in the presence of an excess of oxide-forming metal and aluminum solid solution in copper as well. The possibility is shown of the mechanochemical reduction of copper oxide with aluminum and aluminum solid solution in copper, which is accompanied by the forma-tion of the Сu/Al2O3 composite structure. To modify copper with alumina, using an aluminum solid solution in copper is preferable.

On the exploration of the melting behavior of metallic compounds and solid solutions via multiple classical molecular dynamics approaches: application to Al-based systems.

Classical molecular dynamics simulations of metallic systems have been extensively applied in recent years for the exploration of the energetic behavior of mesoscale structures and for the generation of thermodynamic and physical properties. The evaluation of the conditions leading to the melting of pure metals and alloys is particularly challenging as it involves at one point the simultaneous presence of both a solid and a liquid phase. Defects such as vacancies, dislocation, grain boundaries and pores typically promote the melting of a solid by locally increasing its free energy which favors the destruction of long-range ordering at the origin of this phase transition. In real materials, many of these defects are microscopic and cannot yet be modelled via conventional atomistic simulations. Still, molecular dynamics-based methodologies are commonly used to estimate the melting temperature of solids. These methods involve the use of mesoscale supercells with various nanoscale defects. Moreover, the deterministic nature of classical MD simulations requires the adequate selection of the initial configuration to be melted. In this context, the main objective of this paper is to quantify the precision of the existing classical molecular dynamics computational methods used to evaluate the melting point of pure compounds as well as the solidus/liquidus lines of Al-based binary metallic systems. We also aim to improve the methodology of different approaches such as the void method, the interface method as well as the grain method to obtain a precise evaluation of the melting behavior of pure metals and alloys. We carefully analyzed the importance of the local chemical ordering on the melting behavior. The ins and outs of different numerical methods in predicting the melting temperature via MD are discussed through several examples related to pure metallic elements, congruently and non-congruently melting compounds as well as binary solid solutions. It is shown that the defect distribution of the initial supercell configuration plays an important role upon the description of the melting mechanism of solids leading to a poor predictive capability of melting temperature if not properly controlled. A new methodology based on defect distribution within the initial configuration is proposed to overcome these limitations.