Phase Structure Research Articles

A machine learning assisted preliminary design methodology for bolted composite joints in large structures

Abstract Damage initiation hotspots around features, such as bolts and ply drops, must be investigated during the preliminary design phase of large composite structures, such as composite airframes. A global-local modelling approach is commonly employed to perform this investigation, whereby a global low-fidelity model is used to drive high-fidelity local models around the features of interest. However, this methodology is slow, repetitive and expert-dependent. In this investigation, we address these issues by applying machine learning techniques to this global-local modelling framework and demonstrate the time-saving benefit when predicting damage initiation of bolted composite joints. Feature engineering of model inputs and outputs, and appropriate customisation of machine learning methods enables damage initiation prediction. Special consideration is given to the boundary conditions that must be varied to simulate the response of the bolted composite joints. Results show over three orders of magnitude time-saving benefit and satisfactory accuracy of the proposed methodology. This indicates its potential to be developed further into a rapid design and optimisation tool.

Ru-Incorporation-Induced Phase Transition in Co Nanoparticles for Low-Concentration Nitric Oxide Electroreduction to Ammonia at Low Potential.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3) represents a potential solution for improving the disrupted nitrogen cycle balance. Unfortunately, designing efficient electrocatalysts for NO reduction reaction (NORR) remains a notable challenge, especially at low concentrations. Herein, a displacement-alloying strategy is reported to successfully induce the phase transition of Co nanoparticles supported on carbon nanosheets from face-centered cubic (fcc) to hexagonal close-packed (hcp) structure through Ru incorporation. The obtained RuCo alloy with hcp phase structure (hcp-RuCo) exhibits apparent NORR activity with a record-high Faraday efficiency of 99.2% and an NH3 yield of 77.76µg h-1 mgcat -1 at -0.1V versus reversible hydrogen electrode at a NO concentration of 1vol %, surpassing Co nanoparticles with fcc phase structure and most reported catalysts. Density functional theory calculations reveal that the excellent NORR activity of hcp-RuCo can be attributed to the optimized electronic structure of Co site and lowered energy barrier of the potential rate-determining step through phase transition. Furthermore, the assembled Zn-NO battery using hcp-RuCo as the cathode achieves a power density of 2.33mW cm-2 and an NH3 yield of 45.94µg h-1 mgcat -1. This work provides a promising research perspective for low-concentration NO conversion.

Graphitic carbon nitride-modified cerium ferrite: an efficient photocatalyst for the degradation of ciprofloxacin, ampicillin, and erythromycin in aqueous solution

AbstractIncomplete removal of antibiotics by most known wastewater treatment plants is a global challenge. Therefore, graphitic carbon nitride-modified cerium ferrite (CeFe2O4@g-C3N4) was synthesized to remove antibiotics (ampicillin, ciprofloxacin and erythromycin) from water. CeFe2O4@g-C3N4 showed activity in the visible light with a Tauc plot revealing the bandgap energy (2.46 eV). The scanning electron micrograph (SEM) result revealed the surface of CeFe2O4@g-C3N4 to be heterogeneous, while the transmission electron micrograph (TEM) image confirmed a flaky with rod and oval shaped surface (average particle size of 42.22 nm). CeFe2O4@g-C3N4 exhibited a 100% removal of all the studied antibiotics from aqueous solution in a photocatalytic degradation that is described by pseudo-1st-order kinetics. CeFe2O4@g-C3N4 demonstrated a high regeneration capacity, which is above 90% at the 12th cycle of treatment without any observable changes in its phase structure which suggests a promising chemical stability and reusability. CeFe2O4@g-C3N4 compared favourably with some selected antibiotic degradable photocatalysts suggesting the economic viable of CeFe2O4@g-C3N4 as photocatalyst for the purification of antibiotics-contaminated water. Graphical Abstract

Strain Programming of Oxygen Octahedral Symmetry in Perovskite Oxide Thin Films

AbstractThe collective rotations of oxygen octahedra play an important role in determining the physical properties of functional perovskite oxides. The epitaxial strain can serve as an effective means to modify the oxygen octahedral symmetry (OOS), i.e., oxygen octahedral rotation or tilt (OOR/OOT). However, the strain‐OOS coupling that may alter the details of the OOS, thereby the physical properties, has not been fully understood. In this work, it is demonstrated that epitaxial strain can not only induce a structural phase transition but also precisely tune the degree of OOR. The correlated metal CaNbO3, which is orthorhombic, is studied by growing as epitaxial thin films. By imposing epitaxial strain, it is found that the film undergoes a structural phase transition from orthorhombic to tetragonal upon fully straining (i.e., from a+b−b− to a0a0c−). In unstrained films, the octahedral rotation along the c‐axis is as large as 15.7° that can be tuned to 6.6° by strain. This finding offers a general approach to manipulating OOR/OOT via strain engineering in complex oxide heterostructures.

Three‐Dimensional Imaging of the Structural Phase Transition in a Single Vanadium Dioxide Nanocrystal

Vanadium dioxide (VO2) is a strongly correlated material that exhibits a number of structural phase transitions (SPT) near to room temperature of considerable utility for various technological applications. When reduced to the nanoscale, a foreknowledge of surface and interface properties of VO2 during the SPT can facilitate the development of devices based on VO2. Herein, it is shown that Bragg coherent X‐ray diffractive imaging (BCDI) combined with machine learning is an effective means to recover three‐dimensional images of a single VO2 nanocrystal during a temperature‐induced SPT from a room‐temperature monoclinic phase to a high‐temperature rutile phase. The findings reveal the coexistence of multiple phases within the nanocrystal throughout the transition, along with missing density which indicates the presence of a newly formed rutile phase.

Fabrication and Characterization of Micro-Arc Oxidation Films on β-Titanium Alloy in Silicate and Silicate/Glycerin Electrolyte

Micro-arc oxidation (MAO) films were fabricated on the Ti-39Nb-6Zr alloy at different voltages in the silicate and silicate/glycerin electrolyte. Their morphology, phase structure and composition were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the glycerin additive in the silicate electrolyte improved the compactness of the MAO film. The corrosion resistance was evaluated, and the influence of glycerin additive in electrolyte on the growth of micro-arc oxidized film was revealed by optical emission spectra.

Early Stages of High‐Temperature Oxidation Behavior and Its Phase Evolution of 9% Ni Steel

Herein, the effects of oxygen partial pressure (5–20%) and oxidation time (0.5–6 h) on the growth behavior and phase structure of 9% Ni steel oxide layer are studied by means of high‐temperature oxidation experiment, scanning electron microscopy, and X‐ray diffraction. The results show that the inner and outer oxide layers of 9% Ni steel grow opposite to each other along the initial surface direction of the vertical matrix during the high‐temperature oxidation process. From the perspective of the phase, the phase transition of Fe2O3→Fe3O4→FeO mainly undergoes from the outside and the inside, the results of thermodynamic calculations show that <<<0, and the main factor affecting the phase transition is the diffusion concentration of free O and Fe atoms. During the high‐temperature oxidation process of 9% Ni steel, the diffusion of O and Fe atoms along grain boundaries promotes preferential oxidation at these boundaries. The columnar structure formed in the outer oxide layer of 9% Ni steel may be related to the uneven diffusion rate of Fe atoms at different positions at the interface between the inner and outer oxide layers.

Identifying and controlling the order parameter for ultrafast photoinduced phase transitions in thermosalient materials

The drastic shape deformation that accompanies the structural phase transition in thermosalient materials offers great potential for their applications as actuators and sensors. The microscopic origin of this fascinating effect has so far remained obscure, while for technological applications, it is important to learn how to drive transitions from one phase to another. Here, we present a combined computational and experimental study, in which we have successfully identified the order parameter for the thermosalient phase transition in the molecular crystal 2,7-di([1,1'-biphenyl]-4-yl)-fluorenone. Molecular dynamics simulations reveal that the transition barrier vanishes at the transition temperature. The simulations further show that two low-frequency vibrational-librational modes are directly related to the order parameter that describes this phase transition, which is supported by experimental Raman spectroscopy studies. By applying a computational THz pulse with the proper frequency and amplitude we predict that we can photoinduce this phase transition on a picosecond timescale.

Kinetics Enhancement of High‐Voltage LCO via In‐Situ Formed Cyanide‐Rich Polymer Interfaces

AbstractLithium cobalt oxide (LiCoO2) is widely used as cathode material for lithium‐ion batteries due to its high operation voltage and high specific capacity. However, conventional LiCoO2 (LCO) undergoes severe structural phase transitions and compositional changes at high voltage (>4.4 V) leading to failure. Herein, a multifunctional crosslinked polymer interface is insitu formed on LCO particles, which can build a nanoscale conformal coating layer on the interface of LCO, preventing the side reaction with the electrolyte. Moreover, thanks to its high‐voltage talerances and high Li+ conductivity, the in‐situ polymerized interface has excellent high‐voltage stability and Li+ transport kinetics, which significantly improves the electrochemical performances of LCO at 4.55 or 4.6 V. This study confirms the feasibility of in situ polymer modification of LCO, providing new ideas and methods for the structural stabilization and performance enhancement of high‐voltage lithium cobalt oxides.

Phase Transformation on Two-Dimensional MoTe2 Films for Surface-Enhanced Raman Spectroscopy

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy (SERS) owing to their atomically flat surfaces and adjustable electronic properties. Herein, large-scale 2D 1T′- and 2H-MoTe2 films were prepared using a chemical vapor deposition method. We found that phase structure plays an important role in the enhancement of the SERS performances of MoTe2 films. 1T′-MoTe2 films showed a strong SERS effect with a detection limit of 1 × 10−9 M for the R6G molecule, which is one order of magnitude lower than that of 2H-MoTe2 films. We demonstrated that the SERS sensitivity of MoTe2 films is derived from the efficient photoinduced charge transfer process between MoTe2 and adsorbed molecules. Moreover, a prohibited fish drug could be detected by using 1T′-MoTe2 films as SERS substrates. Our study paves the way to the development and application of high-performance SERS substrates based on TMD phase engineering.

Composite underwater optical wireless channel modeling based on the electric field Monte Carlo method

In this study, we propose a simulation method to investigate the scattering characteristics of beams with specific phase structures in waters containing micrometer-scale particles and bubbles. This method is based on the electric field Monte Carlo (EMC) algorithm and utilizes the Mie theory and ray tracing method. We simulate the propagation of orbital angular momentum (OAM) beams in a composite underwater channel using the proposed method and analyze the impact of bubble density on the spiral phase distribution of the OAM beams. We also design an underwater experiment in a water tank to simulate the propagation of OAM beams in the composite channel. The results reveal that the power of the desired mode of the OAM beam decreases as the bubble density increases, which is consistent with the simulation results. This method facilitates a realistic simulation of structured light beam propagation in waters containing particles and bubbles and can provide reference data for studying the scattering characteristics of structured beams in composite underwater channels.

Synthesis of Side-Chain Liquid Crystalline Polyacrylates with Bridged Stilbene Mesogens

In recent years, π-conjugated liquid crystalline molecules with optoelectronic functionalities have garnered considerable attention, and integrating these molecules into side-chain liquid crystalline polymers (SCLCPs) holds potential for developing devices that are operational near room temperature. However, it is difficult to design SCLCPs with excellent processability because liquid crystalline mesogens are rigid rods, have low solubility in organic solvents, and have a high isotropization temperature. Recently, we developed near-room-temperature π-conjugated nematic liquid crystals based on “bridged stilbene”. In this work, we synthesized a polyacrylate SCLCP incorporating a bridged stilbene that exhibited a nematic phase near room temperature and could maintain liquid crystallinity for more than three months. We conducted a thorough phase structure analysis and evaluated the optical properties. The birefringence values of the resulting polymers were higher than those of the corresponding monomers because of the enhanced order parameters due to the polymer effect. In addition, the synthesized polymers inherited mesogen-derived AIE properties, with high quantum yields (Φfl = 0.14–0.35) in the solid state. It is noteworthy that the maximum fluorescence wavelength exhibited a redshift of greater than 27 nm as a consequence of film formation. Thus, several unique characteristics of the SCLCPs are unattainable with small molecular systems.

Riemann surfaces and winding numbers of Rényi phase structure of charged-flat black holes

It’s widely recognized that the free energy landscape captures the essentials of thermodynamic phase transitions. In this work, we extend the findings of [1] by incorporating the nonextensive nature of black hole entropy. Specifically, the connection between black hole phase transitions and the winding number of Riemann surfaces derived through complex analysis is extended to the Rényi entropy framework. This new geometrical and nonextensive formalism is employed to predict the phase portraits of charged-flat black holes within both the canonical and grand canonical ensembles. Furthermore, we elucidate novel relations between the number of sheets comprising the Riemann surface of the Hawking–Page and Van der Waals transitions and the dimensionality of black hole spacetimes. Notably, these new numbers are consistent with those found for charged-AdS black holes in Gibbs–Boltzmann statistics, providing another significant example of the potential connection between the cosmological constant and the nonextensive Rényi parameter.

Temperature-Governed Microstructure of Poly(vinyl alcohol) Hydrogels Prepared through Mixed-Solvent-Induced Phase Separation.

The formation of phase-separated structures in hydrogels plays a crucial role in determining their optical and mechanical properties. Traditionally, phase-separated hydrogels are prepared through a two-step process involving initial hydrogel synthesis followed by post-treatment. In this study, we present an approach for temperature-governed phase separation microstructure modulation in hydrogels, harnessing the cononsolvency effect. This method allows the phase-separated structure to develop during hydrogel synthesis, significantly simplifying the preparation process. Importantly, we found that the preparation temperature has a substantial effect on the internal structure of the phase-separated hydrogel. We systematically investigated how the temperature influences the phase structure, optical properties, and mechanical performance of these hydrogels. The resulting hydrogels demonstrate excellent moisturizing and antifreezing capabilities. Additionally, the incorporation of sodium chloride imparts remarkable electrical conductivity to the hydrogels, making them suitable for strain sensing applications across a wide temperature range.

Liquid Crystal Promoted Self-Assembly of Statistical Copolymers into Diverse Nanostructures with Precise Dimensions.

In both natural and synthetic systems, the segregation of multicomponent entities is vital for regulating functions and the ultimate usage of materials. To accomplish the desired properties via nanosegregation or microphase separation, great effort is usually demanded in the synthesis. For example, microphase-separated block copolymers rely on the delicate controlled/living polymerization of different monomers in sequence. Here, we demonstrate that a facile one-pot copolymerization can generate statistical side-chain copolymers exhibiting well-defined and diverse nanostructures. Two hemiphasmidic (or wedge-shaped) cyclooctene monomers were designed, differing in the peripheral tails of the wedges (dodecyl vs. tetraethylene glycol), with lengths of ca. 1 nm. When combining the two monomers together, the statistical copolymers can show columnar liquid crystal (LC) phase and microphase-separated structures of the two monomers, including sphere, cylinder, double gyroid, and lamella. To the best of our knowledge, this is the first time the gyroid phase has been achieved in statistical copolymers. We further demonstrate that changing the side chains to calamitic (or rod-like) mesogens or the backbone to less flexible polynorbornene, the statistical copolymers can also undergo microphase separation of the side chains. The intrinsic self-assembly scheme of statistical copolymers with mesogenic side chains, which are chemically accurate, affords the resultant nanostructures with precise periodicities at the 10- or sub-10-nm scale. Given the small chemical difference between the side-chain tails, microphase separation is promoted by the anisotropic packing of mesogens. It is validated that the statistical side-chain LC copolymers can be a versatile platform for creating nanostructured materials with tailored functionalities.

Study on Microstructure and Properties of AlCoCrFeNi High-Entropy Alloys by Extreme High-Speed Laser Cladding

AlCoCrFeNi HEA powders were cladded onto AISI 1045 steel using EHLA and CLA, respectively. The phase composition, microstructure, micro/nanohardness, and corrosion resistance of the two coatings were compared and analyzed. The results show that the phase structure of AlCoCrFeNi HEA coatings prepared by EHLA and CLA was that of a BCC/B2 phase solid solution. From the bottom to the top, the EHLA-derived AlCoCrFeNi HEA coating experienced evolution in the microstructure of plane crystal, dendrite, and equiaxed crystal. The micro/nanohardness of EHLA-derived coating (~507 HV0.2, 6.716 GPa) is higher than that of CLA-derived coating (~429 HV0.2, 5.778 GPa). The electrochemical test results show that the Ecorr of CLA is −0.527 V and the Icorr of CLA is 1.272 × 10−7 A/cm2, while the Ecorr of EHLA is −0.454 V and the Icorr of EHLA is 1.588 × 10−8 A/cm2, which means that the corrosion resistance of EHLA is better.

A novel red-emitting InScW3O12:Eu3+ phosphor with anti-thermal-quenching performance for high-power WLED applications

A series of red-emitting InScW3O12:Eu3+ (ISWO:Eu3+) phosphors with anti-thermal-quenching performance were successfully synthesized by conventional solid-state reaction. The phase structure and luminescent properties of ISWO:Eu3+ were systematically studied. The photoluminescence excitation (PLE) spectrum showed that ISWO:Eu3+ phosphor can be effectively matched with commercial ultraviolet (UV), violet and blue light chips. The main emission peak of the phosphor was located at 613 nm, which was attributed to the electric dipole transition 5D0 → 7F2. Under the optimal excitation, the prepared ISWO:0.08Eu3+ phosphor showed excellent anti-thermal-quenching performance, its photoluminescence (PL) intensity at 180 °C reached 157.4 % of initial intensity at room temperature. At 465 nm excitation, it also exhibited the anti-thermal-quenching property and the PL intensity remained 115.1 % at 150 °C of that at room temperature. In situ XRD analysis revealed that the lattice contraction resulting in an increase in structural rigidity as the temperature rising, which caused the change of Eu3+ local environment and improved the PL intensity. Finally, a series of warm white LED devices under varying power density conditions with stable output were prepared using the red ISWO:0.08Eu3+ phosphor, indicating that the ISWO:Eu3+ phosphor with excellent anti-thermal-quenching performance has potential application prospects in high-power white light-emitting diodes (WLEDs).

Investigating the thermal-chemical-mechanical coupling effects on the cracking behavior of machine gun barrel: Microstructural insights

The presence of severe cracks at the inner bore of the gun barrel accelerates the erosion failure, whereas the evolution and failure mechanism of crack tips under the thermal-chemical-mechanical coupling effects needs further investigation. Herein, the elemental distribution, phase structure, and strain surrounding the perpendicular and circumferential cracks in a failed gun barrel were investigated in detail by utilizing scanning electron microscopy (SEM), transmission Kikuchi diffraction (TKD), and transmission electron microscopy (TEM). Results indicated that the perpendicular crack was covered by double continuous layers composed of inner FeO oxides and outer Fe0.96S sulfides. Notably, a high-density precipitation of FeO oxides together with severe lattice distortion and localized amorphization was observed at the crack tip, accelerating the growth of the cracks. For the circumferential crack, the presence of fine recrystallized grains alongside coarsened M23C6 carbides was observed at the crack tip. There was a high level of strain concentration along high-angle grain boundaries at the forefront of the circumferential crack tip, resulting in the cracking along grain boundaries. Furthermore, the models for propagation of perpendicular and circumferential cracks under the thermal-chemical-mechanical coupling effects were proposed respectively.

Efficient carburization of high-entropy alloys from polyethylene microplastics using a green mechanochemical process to obtain excellent wave absorbing performance

Polyethylene as a major white pollutant has a significant negative impact on the environment and the human health. Beneficial recycling of polyethylene through mechanochemical processes not only can eliminate environmental hazards, but also enable some beneficial industrial applications. In this work, polyethylene was used as the raw materials of carburization of FeCoNiMn high-entropy alloys (HEAs) by a green mechanochemical method. The phase structure, magnetic properties, high-temperature oxidation resistance, corrosion resistance and electromagnetic-wave absorbing performance of the obtained carburized HEAs were investigated in detail. The carburized-FeCoNiMn HEAs exhibited excellent corrosion resistance, suggesting great application potential for use in harsh environments. Besides, the impedance matching was optimized and the electromagnetic-wave absorption bandwidth was expanded by this carburization process. Specifically, the reflection loss of C10 (FeCoNiMnC0.1) at 8.88 GHz reached −65.07 dB at a thickness of 2.79 mm, and both the C50 (FeCoNiMnC0.5) and C90 (FeCoNiMnC0.9) exhibited a maximum absorption bandwidth of 5.45 GHz. This work provides a new concept of utilizing common microplastic pollutants to achieve efficient carburization of HEAs by a green mechanochemical process.

Correlation Between the Crystal Structure and Magnetic Properties of Bi1−yCayFe1−xMnxO3 Multiferroics near the Polar-Anti(non)polar Phase Boundary

This paper reports the results of a systematic investigation into the magnetic properties of Bi1−yCayFe1−xMnxO3 (0.1 ≤ y ≤ 0.175, 0.35 ≤ x ≤ 0.45) solid solutions. The substitution of Bi3+ with Ca2+ and the concurrent introduction of Mn3+/Mn4+ ions result in the stabilization of various structural phases, with each exhibiting distinct magnetic characteristics. The investigation indicates that the samples containing the polar rhombohedral phase display metamagnetic transitions at low temperatures, characterized by pronounced jumps in magnetization. Single-phase samples with a nonpolar orthorhombic structure exhibit weak ferromagnetic behavior without metamagnetic features. The observed metamagnetic behavior, accompanied by anomalies in temperature-dependent magnetization and significant remnant magnetization at low temperatures, particularly in samples near the polar-anti(non)polar phase boundary, highlighted the presence of both antiferromagnetic and glassy magnetic components.