Metastable Interface Research Articles

Coarsening mechanism of over-aged δ-Ni2Si nanoscale precipitates in Cu-Ni-Si-Cr-Mg alloy

δ-Ni2Si precipitate is the crucial strengthening phase in Cu-Ni-Si alloy, and its coarsening behavior and mechanism impose dramatic effects on mechanical properties. In this paper, Cu-3Ni-0.7Si-0.1Cr-0.05 Mg (wt%) alloy was prepared to systematically investigate the coarsening behavior and elucidate the coarsening mechanism of δ-Ni2Si precipitate during over-aging treatment. Featured core-shell structure was observed via careful characterization during coarsening of δ-Ni2Si phase. Specifically, the core structure was stable δ-Ni2Si, while the shell structure was a metastable interface composed of Cu, Ni and Si elements. At later over-aging stage, the core-shell structure completely transformed into a stable and coarsened δ-Ni2Si phase being coherent with the Cu matrix. It is confirmed for the first time that the coarsening process of δ-Ni2Si precipitate can be interpreted by the trans-interface-diffusion-controlled (TIDC) coarsening theory. The core-shell structure was caused by the disparity between the diffusion activation energy and diffusion rate of Ni, Si, and Cu from the perspective of diffusion kinetics. Moreover, the presence of trace amounts of Cr and Mg components exhibited little effect on the coarsening process of δ-Ni2Si. During over-aging, tensile strength dramatically decreased owing to diminishing precipitation strengthening effect from coarsening of δ-Ni2Si precipitates.

Determination on the Metastable Interface Structure of Nb/MgO(100) Interface

The metastable interface structures between Nb thin films and MgO(100) substrate are investigated using first‐principles calculation. Based on the calculation results of interface separation works for 25 interface models, three metastable interfaces and one stable interface are identified. The growth orientations of Nb films in both the metastable and stable interfaces are found to be Nb[110] and Nb[100], respectively, which align with previous experimental findings. This suggests that it is feasible to predict the metastable interfaces in metal/oxide interface systems by calculating interface energy. Additionally, a comparison is conducted between the stable and metastable interfaces. The metastable interface exhibits a lower interface separation work and lower system energy compared to the stable interface. Herein, it is indicated that the interface separation work plays a key role in determining the metastable interface structure of Nb/MgO(100), rather than the total energy of the entire interface system.

Electrocatalytic CO 2 Reduction over Bimetallic Bi-Based Catalysts: A Review

Electrocatalytic CO ₂ Reduction over Bimetallic Bi-Based Catalysts: A Review

Metastable Metal–Alloy Interface in RuNi Nanoplates Boosts Highly Efficient Hydrogen Electrocatalysis

Designing a unique metastable interface provides a promising way to achieve high catalytic performance yet remains a great challenge due to the thermodynamics’ unstable nature. In this work, we constructed the stabilized metastable interface between metastable ruthenium–nickel alloy and metastable hexagonal–close-packed nickel via a one-step solvothermal method. The optimized nanocatalyst (denoted as hcp RuNi) shows bifunctional performance toward electrochemical hydrogen oxidation and evolution reactions (HOR/HER). Density functional theory calculations reveal that two different reaction sites at the unique interface contribute to the enhanced HER and HOR performances. This work highlights the important role on interface engineering of metastable materials for highly efficient catalysis.

First-principles investigation on electronic structures and energetic characteristics of γ/γ tilt grain boundaries in γ-TiAl intermetallic

The energetic and electronic characteristics of γ/γ tilt grain boundaries (GBs) in γ-TiAl intermetallic were comprehensively analyzed using first-principles methods. The interfacial bonding energy, strength, and features of GBs were quantitatively and qualitatively described by the formation energy, excess free volume (EFV), electron localization function (ELF), bonding charge density (Δρ), and density of states (DOS). The formation energies and EFV of Σ3, Σ11, and Σ5 GBs are relatively low in sequence among different GBs. The electronic structure analyses manifested that the smaller the local lattice strain, the stronger the Ti-d-Al-p bonding, the weaker Al-p-Al-p bonding nearby the GB interface, and the lower the GB formation energy. Further, the interface structure of Σ11 GBs in Widmanstätten structure and that of Σ5 GBs in feathery structure were firstly characterized by TEM. Based on the analyses, the interfacial energetic mechanism of metastable transformations, and possible alloying effects were discussed. This work provides an insight into not only the atomic and electronic basis of GBs but also the understanding of the mechanism of metastable transformations and interface engineering in γ-TiAl alloy.

Structural and Electrolyte Properties of Li18P6N16: A First-Principles Computational Study

In this work we report our First–Principles simulations results of the electrolyte properties of Li 18 P 6 N 16. The obtained simulations of the idealized electrolyte properties suggest that this material is promising solid electrolyte for usage in Li-Ion batteries having Li anode. The simulated crystal structure of this material is found to be in good agreement with experimental data. The phase transition of LiPN2 and Li7PN4 to Li 18 P 6 N 16 at high pressure has been validated through the simulations and found to be in consistent with experiment. The simulations of idealized interfaces with metallic Li anode demonstrate that studied material is likely to form a metastable interface with Li metal. The Li − ion migration analysis suggests that the Li ion migration is dominated with the vacancy migration mechanism which takes place along the c − axis only in Li 18 P 6 N 16. The calculated value of the Li − ion migration activation energy was found to be in good agreement with experiment suggesting that this material possess a promising Li ion conductivity.

High surface area MnO2 catalysts prepared by a metastable aqueous-aqueous interface method and their catalytic oxidation activity

In this work, the metastable aqueous-aqueous interfacial approach was used to prepare MnO2 with enhanced surface area, which helps to save energy, decrease cost and protect the environment. The material characteristic success was proven through using powder X-ray diffraction for the crystalline properties and N2 adsorption-desorption isotherm for high surface area. The relationship between the calcination temperature and the crystallinity as well the specific material surface area was also interested. The catalytic decomposition of hydrogen peroxide was investigated by the closed system measuring produced oxygen. After the H2O2 decomposition comparison between synthesized samples and commercial MnO2 in terms of both the efficiency and the speed, the M-200 sample was considered as a typical sample with outstanding performance to examine the reaction conditions (H2O2 solution concentration, catalyst amount and reaction temperature). The optimal reaction condition results are 0.9% H2O2 solution concentration, 0.2g/L catalyst, and room temperature. Besides, the leaching test and the catalytic regeneration were also conducted.

Metastable five-fold twinned Ru incorporated Cu nanosheets with Pt-like hydrogen evolution kinetics

Precisely tuning the geometric and phase structure of noble metal-based heterostructure nanomaterials has been an effective way to induce a metastable defect interface system for the fast hydrogen evolution reaction (HER) kinetics in alkaline media. However, the unstable defect nature of metastable materials hinders their practical applications. Herein, as demonstrated by the theoretical calculation, the optimal Gibbs free energy of adsorbed H2O (ΔGH2O) and water dissociation (ΔGB) can be created for five-fold twinned Ru on Cu NSs with metastable interfaces. Thus, we successfully design and construct an in-situ metastable interface in five-fold twinned Ru supported on vertically oriented Cu nanosheets (Cu NSs) (devoted as CuRux NSs). Among them, CuRu8 NSs display unprecedented overpotentials of 8 and 39 mV at 10 and 100 mA cm−2, respectively. Furthermore, CuRu8 NSs also demonstrate high intrinsic mass activity of 77.528 A g−1 at an overpotential of 20 mV and a large exchange current density of 5.014 mA cm−2, with outstanding stability (almost no activity degradation for 130 h). These represent one of the best alkaline HER catalysts to date for Ru-based catalysts. Importantly, CuRu8 NSs possess nearly 100% Faradaic yield, confirming the high selectivity toward hydrogen evolution reaction. Furthermore, the fine structural analysis evidences that the in-situ incorporated five-fold twinned Ru nanoparticles coupled electronically with Cu NSs not only avoid migration and aggregation of the metal particles, but also effectively promote the formation of heterostructure nanosheet arrays with abundant active sites, enhancing the alkaline hydrogen evolution kinetics.

Fabrication of Bi/Sn bimetallic electrode for high-performance electrochemical reduction of carbon dioxide to formate

CO2 electrochemical reduction (CO2ER) can convert CO2 into value-added liquid fuel, which can not only mitigate the global warming problem caused by CO2, but also can be used for energy storage in the form of intermittent renewable energy. High-performance catalysts are required in order to efficiently conduct electrochemical carbon dioxide reduction under mild conditions. In this work, the bimetallic bismuth and tin were deposited on the copper mesh via a simple and speedy electrodeposition strategy and assessed as electrocatalysts for the conversion of CO2 to formate. The Bi5Sn60 electrode (bismuth deposition time of 5 min, tin deposition time of 60 min) exhibited an excellent catalytic activity with a remarkably high Faradaic efficiency of 94.8% and partial current density of 34.0 mA cm−2 at − 1.0 V vs RHE. More intriguingly, it exhibited a remarkable formate production rate of 634.3 μmol cm−2h−1 that outperformed most of the reported electrocatalysts. The pine needle-shaped dendritic structures could provide a considerable surface area and massive active sites. The fast electron transfer was of great benefit to the formation of CO2• − intermediate. The metal oxide/metal metastable interface was conducive to stabilizing the CO2• − intermediate and inhibiting the hydrogen evolution reaction (HER) process. Moreover, the optimized electronic structure strengthened the pathway related to the OCHO• intermediate, thereby boosted the conversion of CO2 to formate. The results demonstrated that the dendrite structured Bi/Sn bimetallic catalysts would be a promising candidate for high-efficiency CO2 reduction.

Metastable interface biomimetic synthesis of a smart nanosystem for enhanced starvation/gas therapy

Glucose oxidase (GOx)-mediated starvation therapy holds great promise in cancer treatment. However, the worse hypoxia conditions result into low therapeutic efficiency, and undegradability of carriers poses potential threats to living bodies. To address this, herein a bioinspired MnO2 nanosystem with controllable surface was developed for highly efficient starvation/gas synergistic enhanced therapy. Biomimetic design and further surface modification unprecedentedly endowed the nanosystem with ultrahigh loading capacity for GOx and l-Arginine (l-Arg) and special selectivity toward cancer cells. Especially, the dissipative O2 during starvation therapy was well replenished by a positive cycle formed by the nanosystem, which continuously reproduced O2 and accelerated glucose consumption. The abundant H2O2 was further used to oxidize l-Arg into nitric oxide to realize gas therapy. In vitro and in vivo testing confirmed that this new treatment effectively blocked the nutrition and energy sources of cells to obtain excellent therapeutic effect. We reported the first experimental item of this nanosystem for inhibiting cancer cell migration. Considering the novel design concept with facile biomimetic methods, effective co-loading of endogenous substances, and good anti-tumor and anti-migration effects, this work provided new theoretical and experimental basis for starvation therapy and inspired people to design more delicate platform for cancer treatment.

Low‐Resistive LiCoO2/Li1.3Al0.3Ti2(PO4)3 Interface Formation by Low‐Temperature Annealing Using Aerosol Deposition

Interfacial resistance at electrode‐high Li+ conductive solid electrolytes must be reduced well to develop high‐power all‐solid‐state batteries using oxide‐based solid electrolytes (Ox‐SSBs). Herein, crystalline electrode films of LiCoO2 (LCO) are formed on a high Li+ conductive crystalline‐glass solid electrolyte sheet, Li1.3Al0.3Ti2(PO4)3 (LATP) (σ25 °C = 1 × 10−4 S cm−1), at room temperature by aerosol deposition (AD), and the effects of the annealing temperature on the interfacial resistivities (Rint) at the LCO/LATP are investigated. The Rint visibly increases by annealing over 500 °C with the growth of Co3O4 as a reactant. In contrast, Rint is reduced to ≈100 Ω cm2 by low‐temperature annealing at 250–350 °C due to superior contact through the structural rearrangement of an artificial metastable interface formed by the AD. These results are applied to bulk‐type Ox‐SSB, Li/Li7La3Zr2O12(LLZ)/LCO–LATP, and our best Ox‐SSB delivers a discharge capacity of 100 mA cm−2 at 100 °C.

Unique Properties of Tightly Docked Membranes Prior to their Fusion

Membrane merger through fusion is essential in myriad of processes including neurotransmission and viral infection. Although there are various classes of fusion proteins, they are believed to catalyze membrane fusion through a common pathway. Despite the importance of understanding of this process, the exact mechanisms underlying steps immediately before the first bilayer disruption remain uncharacterized. Here, we characterized mechanism leading to a change in lipid arrangement in membranes arrested in a state that precedes hemifusion. Such tightly adhering membranes with a distance of <1 nm are known from cryo-electron microscopy as fusion intermediates of trafficking organelles, mitochondria, or during cell entry by enveloped viruses. With the use of an in vitro reconstitution system consisting of lipid vesicles with SNARE proteins, we demonstrate formation of a metastable, divalent cation-independent, and protein-free membrane-membrane interface characterized by increased thickness. Furthermore, we confirm that structural rearrangements in the membranes are arising due to membrane intrinsic properties by performing all-atom molecular dynamics simulations of double-membrane systems at varying distances. In turn, we would like to propose that increase in membrane thickness arises by dehydration-driven lipid headgroup tilting leading to lateral area shrinkage that results in increased bilayer thickness visible in experiments.

Designing a high-reflectivity normal-incidence Ge/Si multilayer X-ray mirror for the 44–50 nm wavelength range

For many years, the Mo/Si multilayer mirror has been the standard choice for normal incidence optics in the EUV/X-ray range below 20 nm. As one goes to longer wavelengths, such as the 46.9 nm Ne-like Ar X-ray laser, the absorption in Mo increases substantially, which is why the Sc/Si mirror was developed to operate in this region. To solve the problem of the metastable interface of Sc/Si mirrors due to diffusion between the two materials, this paper looks at an alternative Ge/Si multilayer mirror that replaces Sc with Ge, which offers potential advantages for fabricating a multilayer structure without the additional diffusion barriers needed with Sc. Ge can also be used to produce a narrow band filter in this wavelength regime.

Deep insights into the solution and interface behaviors in heavy rare earth extraction: A molecular dynamics study

Heavy rare earth extraction (HRE) is a complex process involving extractant partition, complexation at metastable oil-water interface and cation separation from aqueous phase to organic phase. Beyond the coordination chemistry of the HRE extracted complex, the solution and interfacial behaviors can be crucial to extractant distribution, orientation and reactivity of ionic species for understanding and further improving the extraction performance. We report a molecular dynamics investigation on dilute and concentrated solutions of four acidic organophosphoric extractants (P507, P204, P227 and Cyanex272) in pure oil phase and oil-water biphasic systems for purpose of depicting solution and interface behaviors, which has been a cornerstone of chemistry in solvent extraction and separation. We can intuitively find that the single extractant promotes the interface movement. When the extractants get concentrated in organic phase, they diffuse and aggregate to dimers and trimers. In oil-water biphasic system, most of the extractants tend to migrate to the interface and remain an excess adsorption phenomenon, where –OH groups point towards water and are ready to capture an approaching HRE cation. Some important findings of different extractants are determined by theoretical simulation, such as interfacial activity, residual water number in equilibrated organic phase and capture time of HRE cation. These simulated quantitative features are in good agreement with the experiments of interfacial tension, phase separation and kinetic extraction. The results indicate the key role of the amphiphilic moiety, the oxygen atoms of P–O ester linkages and the hydrophobicity of P–C ester linkages of extractants in the HRE extraction process. This MD study could provide a straightforward approach to comprehensively evaluate and design the extractants for liquid-liquid solvent extraction in future.

On the use of metastable interface equilibrium assumptions on prediction of solidification micro-segregation in laser powder bed fusion

ABSTRACTMany models have been developed to explore solidification segregation and dendrite structure in additively manufactured parts. However, these models tend to be computationally expensive and consider only a limited number of alloying elements, compromising their practical application. In this work, a methodology to extend the Scheil model, based on interface metastable equilibrium assumptions, is established to predict the spatial compositional maps due to micro-segregation for a laser-powder bed fusion (L-PBF) build of alloy 718. The compositional maps are contrasted against experimental data measured in a unit dendrite cell by transmission electron microcopy. The validity of Scheil's implicit assumptions under the rapid solidification conditions in L-PBF is further discussed. The extended Scheil model is shown to be computationally efficient and readily applicable to multi-component systems.

Preparation, properties and modification mechanism of polyurethane modified emulsified asphalt

To prepare new polyurethane (PU) modified emulsified asphalt (EA), and further understand modification mechanism of PU to EA, effects of PU on basic engineering performances, chemical composition compatibility, morphology and element compositions, thermal properties, phase microstructures of EA were discussed. The results indicate that basic properties of PU modified EA firstly meet relevant requirements of technical specifications. Improvement effects of PU with a suitable content on penetration and ductility is better than that of styrene butadiene styrene (SBS), but their softening points are similar. Secondly, PU modified EA process includes physical and chemical modifications. PU is dispersed uniformly in evaporation residues of EA when PU content is less than 6%, and meta-stable two-phase interface transition layers are formed between PU and asphalt binder, forming a uniform dispersion system and interpenetrating network structures in modified EA. The compatibility between PU and EA is satisfactory, forming a stable multiphase structure in modified EA. This is conductive to improve high-temperature stability and low-temperature ductility of modified EA. Thirdly, the contents of such main chemical elements as carbon (C), oxygen (O) and sulfur (S) in evaporation residues of EA show no obvious changes before and after modified by PU, indicating that physical modification is main method during the preparation of PU modified EA. Fourthly, PU is difficult to form a continuous crystalline phase in EA. However, the molecular chain spacing and microcrystalline size of PU modified EA are decreased at a suitable PU content, generating more compact interpenetrating network of molecular chains. Motions of asphalt molecules are limited, improving thermal stability and mechanical properties of EA. Finally, a suitable PU content of 6% is proposed to prepare modified EA.

Electrochemical Stability of Closo-Carborane Anions and Their Impact on Cathode Interfacial Properties

Electrochemically stable, charge delocalized anions are essential electrolyte constituents for rechargeable, high voltage magnesium batteries. Within this class of anions, magnesium closo-carborane salts were demonstrated to support reversible magnesium electrodeposition/dissolution in tetraethylene glycol dimethyl ether (tetraglyme, G4) highlighting their cathodic stability.1,2 The corresponding anodic stability of these anions remains undetermined due to the lower anodic stability of the glyme solvents preferred for increased salt solubility, ionic conductivity, and stability against magnesium metal. In this paper, we explore the anodic stability of the carba-closo-dodecaborate anion (CB11H12 -) and select functionalized derivatives thereof relative to the more typical battery electrolyte anions bis(trifluoromethylsulfonyl)imide (TFSI) and tetrafluoroborate (BF4). In solvents of higher anodic stability than the glymes, including 3-methylsulfolane and 1,1,3,3-hexafluoroisopropanol, we demonstrate an oxidation potential of 4.5 V vs. Mg/Mg(II) for the base CB11H12 - anion, which is surprisingly lower than that measured for TFSI or BF4. Computational screening of the adiabatic ionization potential and electron affinity of RCB11H11 - (where R is a functional group that replaces the H-C proton) indicates that substitution of the proton at the carbon vertex with an electron withdrawing group can yield a several hundred millivolt increase in oxidative stability without decreasing the cathodic stability. Synthesis and electrochemical evaluation of the fluoro-carba-closo-dodecaborate validates this prediction and offers a rational design strategy for improved electrolyte stability. Oxidation of either the parent or substituted carba-closo-dodecaborate anion is irreversible, resulting in a neutral radical that incorporates within a surface film. The surface film formed inhibits further electron transfer leading to a varying degree of passivation toward further electrolyte decomposition depending on the solvent employed. The composition and structure of this metastable interface and its Mg cation transport properties will be discussed. O. Tutusaus, R. Mohtadi, T.S. Arthur, F. Mizuno, E.G. Nelson, Y.V. Sevryugina, “An Efficient Halogen-Free Electrolyte for Use in Rechargeable Magnesium Batteries,” Angew. Chem. Int. Ed. 2015, 54, 7900.S.G. McArthur, R. Jay, L. Geng, J. Guo, V. Lavallo, “Below the 12-vertex: 10-vertex carborane anions as non-corrosive, halide free, electrolytes for rechargeable Mg batteries,” Chem. Comm. 2017, 53, 4453.

Identifying metastable interface potency limits during steel alloy transformations

In ferrous systems the transformation from ferrite to austenite involves solid-phase nucleation of the stable phase along a pre-existing metastable grain boundaries. Analysis of the thermodynamics controlling phase selection are re-evaluated based on newly published results of atomistic simulations that quantify grain tilt-boundary surface energy. Nucleation does not occur until some critical misorientation develops through dislocation association such that the grain boundary becomes a potent nucleation site.

Initial Collision Process of Two Miscible Droplets.

Dynamic properties of the metastable interface between two miscible solutions are investigated by the collision of two droplets. A clear interface is observed between the two colliding droplets. The interface moves in the colliding droplet toward the side where the original droplet has a lower surface tension. The interface is set to the middle of the colliding droplet by controlling the surface tension of the droplets to observe the chemical reactions at the droplet interface by cavity-enhanced Raman spectroscopy. This study provides a foundation for further research on the initial process of the chemical reactions of two miscible solutions.

Synthesis of high surface area mesoporous MnO2 via a “metastable” aqueous interfacial reaction

In this work, a metastable aqueous interface was fabricated for synthesizing mesoporous and high surface area MnO2. When urea was used as the additive, hierarchical spheres self-organized from ultrathin nano-sheets were obtained. Its porous structure could be controlled through adjusting the urea concentration, and a maximum surface area of 407m2 g−1 was achieved by this method, which is larger than the reported values. Due to the porous structure and high surface area, as-prepared MnO2 exhibited a specific capacitance of 775.4 F g−1 at a current density of 0.1 A g−1, and exhibited a 63.5% capacitance retention when the current density was increased from 0.1 A g−1 to 5A g−1. Durability studies showed a 63.7% capacitance retention after 2500 cycles. The metastable interfacial reaction approach could also be extended to other alloys with large surface area and porous structure, such as CoB alloy. This method provides a simple and low-cost method to synthesize high surface area and mesoporous materials.