Phase Properties Research Articles

Effect of dissolved KOH and NaCl on the solubility of water in hydrogen: A Monte Carlo simulation study.

Vapor-Liquid Equilibria (VLE) of hydrogen (H2) and aqueous electrolyte (KOH and NaCl) solutions are central to numerous industrial applications such as alkaline electrolysis and underground hydrogen storage. Continuous fractional component Monte Carlo simulations are performed to compute the VLE of H2 and aqueous electrolyte solutions at 298-423K, 10-400bar, 0-8 molKOH/kg water, and 0-6 molNaCl/kg water. The densities and activities of water in aqueous KOH and NaCl solutions are accurately modeled (within 2% deviation from experiments) using the non-polarizable Madrid-2019 Na+/Cl- ion force fields for NaCl and the Madrid-Transport K+ and Delft Force Field of OH- for KOH, combined with the TIP4P/2005 water force field. A free energy correction (independent of pressure, salt type, and salt molality) is applied to the computed infinite dilution excess chemical potentials of H2 and water, resulting in accurate predictions (within 5% of experiments) for the solubilities of H2 in water and the saturated vapor pressures of water for a temperature range of 298-363K. The compositions of water and H2 are computed using an iterative scheme from the liquid phase excess chemical potentials and densities, in which the gas phase fugacities are computed using the GERG-2008 equation of state. For the first time, the VLE of H2 and aqueous KOH/NaCl systems are accurately captured with respect to experiments (i.e., for both the liquid and gas phase compositions) without compromising the liquid phase properties or performing any refitting of force fields.

Photophysics in Biomembranes: Computational Insight into the Interaction between Lipid Bilayers and Chromophores.

ConspectusLight is ubiquitously available to probe the structure and dynamics of biomolecules and biological tissues. Generally, this cannot be done directly with visible light, because of the absence of absorption by those biomolecules. This problem can be overcome by incorporating organic molecules (chromophores) that show an optical response in the vicinity of those biomolecules. Since those optical properties are strongly dependent on the chromophore's environment, time-resolved spectroscopic studies can provide a wealth of information on biosystems at the molecular scale in a nondestructive way. In this work, we give an overview on the multiscale computational strategy developed by us in the last eight years and prove that theoretical studies and simulations are needed to explain, guide, and predict observations in fluorescence experiments. As we challenge the accepted views on existing probes, we discover unexplored abilities that can discriminate surrounding lipid bilayers and their temperature-dependent as well as solvent-dependent properties. We focus on three archetypal chromophores: diphenylhexatriene (DPH), Laurdan, and azobenzene. Our method shows that conformational changes should not be neglected for the prototype rod-shaped molecule DPH. They determine its position and orientation in a liquid-ordered (Lo) sphingomyelin/cholesterol (SM/Chol) bilayer and are responsible for a strong differentiation of its absorption spectra and fluorescence decay times in dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) membranes, which are at room temperature in liquid-disordered (Ld) and solid-gel (So) phases, respectively. Thanks to its pronounced first excited state dipole moment, Laurdan has long been known as a solvatochromic probe. Since this molecule has however two conformers, we prove that they exhibit different properties in different lipid membrane phases. We see that the two conformers are only blocked in one phase but not in another. Supported by fluorescence anisotropy decay simulations, Laurdan can therefore be regarded as a molecular rotor. Finally, the conformational versatility of azobenzene in saturated Ld lipid bilayers is simulated, along with its photoisomerization pathways. By means of nonadiabatic QM/MM surface hopping analyses (QM/MM-SH), a dual mechanism is found with a torsional mechanism and a slow conversion for trans-to-cis. For cis-to-trans, simulations show a much higher quantum yield and a so-called "pedal-like" mechanism. The differences are related to the different potential energy surfaces as well as the interactions with the surrounding alkyl chains. When tails of increased length are attached to this probe, cis is pushed toward the polar surface, while trans is pulled toward the center of the membrane.

Understanding the Unique Corrosion Phenomenon of Sanxingdui Embrittled Gold Masks Using Scanning Electrochemical Cell Microscopy (SECCM): Intergranular Corrosion of Au-Ag-Pb Ternary Alloy

The study investigated the rare corrosion of embrittled gold masks excavated from the Sanxingdui archaeological site, attributing the embrittlement to preferential corrosion of intergranular Pb-containing phases through morphological studies using metallographic microscopy and SEM-EDS. Scanning electrochemical cell microscopy (SECCM) technology was used to quantitatively analyze simulated Au-Ag-Pb alloy samples to compare the electrochemical properties of different phases at the microscopic level. The results revealed an electrochemical activity order of Au-Ag < Au2Pb < AuPb2+PbxOy, which explains the varying levels of retention for different components in gold masks and provides a reference for subsequent conservation strategy.

The effect of polylactic acid-based blend films modified with various biodegradable polymers on the preservation of strawberries

Polylactic acid (PLA) has garnered much attention in the field of fruit and vegetable packaging. Despite its poor flexibility and water resistance, PLA film faces challenges in being used for strawberry storage and freshness preservation due to its inability to maintain flavor quality. In this study, a series of PLA-based modified films was produced by melt blending and extrusion cast processing with PLA as the main component, along with flexible biodegradable polyesters or polycarbonate as the secondary component. First, five different biodegradable polymers were used to investigate the effect of the flexibility and barrier properties of different dispersed phases on the morphology, mechanical properties, and water vapor barrier of PLA-based blend films. Next, the impact on the freshness of strawberries was assessed through examination of fruit color and weight, as well as the levels of O2 and CO2 in the packaging bags. The results showed that the size of the dispersed phase and interfacial bonding with PLA were the key factors determining the mechanical and barrier properties of the blend films. The PLA-polycaprolactone (PCL) blend showed the best compatibility among them, with PCL having the smallest dispersion size (D=0.58μm), higher toughness than the other four PLA blends, and greater enhancement of PLA. Additionally, it exhibited a similar rate of quality loss in strawberry preservation compared to commercial PE. As a result, the color and luster were more completely preserved. The results of this study may help the future development of degradable plastics, to reduce environmental pollution.

The Quick Determination of a Fibrous Composite’s Axial Young’s Modulus via the FEM

Knowing the mechanical properties of fiber-reinforced composite materials, which are currently widely used in various industrial branches, represents a major objective for designers. This happens when new materials are used that are not yet in production or for which the manufacturer cannot give values. Given the practical importance of this problem, several methods of determining these properties have been proposed, but most of them are laborious and require a long calculation time. And, some of the proposed calculation methods are very approximate, providing only upper and lower limits for these values. Experimental measurements are obviously the optimal solution for solving this problem, but it must be taken into account that this type of method consumes time and material resources. This paper proposes a sufficiently accurate and fast estimation method for determining Young’s modulus for a homogenized fibrous material. Thus, the FEM is used to determine the natural frequencies of a standard bar, for which there are sufficiently precise classical methods to express the engineering constants according to the mechanical properties of the component phases of the homogenized material. In this paper, Young’s modulus is determined for such a material using the relationships that provide the eigenfrequencies for the longitudinal vibrations. With the adopted model, transverse and torsional vibrations are eliminated by blocking the nodes on the surfaces of the bars. In this way, more longitudinal eigenfrequencies can be obtained, so the precision in calculating Young’s modulus is increased.

High Magnetic Performance in MnGa Nanocomposite Magnets

In view of their potential applicability in technology fields where magnets are required to operate at higher temperatures, the class of nanocomposite magnets with little or no rare earth (RE) content has been widely researched in the last two decades. Among these nanocomposite magnets, the subclass of magnetic binary systems exhibiting the formation of L10 tetragonal phases is the most illustrious. Some of the most interesting systems are represented by the Mn-based alloys, with addition of Al, Bi, Ga, Ge. Such alloys are interesting as they are less costly than RE magnets and they show promising magnetic properties. The paper tackles the case of MnGa binary alloys with various compositions around the Mn3Ga stoichiometry. Four MnGa magnetic alloys, with Mn content ranging from 70 at% to 75 at% were produced using rapid solidification to form the melt. By combining structural information arising from X-ray diffractometry and transmission electron microscopy with magnetic properties determined by vibrating sample magnetometry, we are able to document the nature and properties of the structural phases formed in the alloys in their as-cast state and upon annealing, the evolution of the phase structure after annealing and its influence on the magnetic behavior of the MnGa alloys. After annealing at 400 °C and 500 °C, MnGa alloys are showing a multiple-phase microstructure, consisting of co-existing crystallites of L10 and D022 tetragonal phase. As a consequence of these structurally and magnetically different phases, co-existing within the microstructure, promising magnetic features are obtained, with both coercive fields and saturation magnetization exceeding values previously reported for both alloys and layers of MnGa.

Spark plasma sintering of Co-W-Ta ternary superalloys: densification mechanism, phase, microstructural and mechanical properties

Spark plasma sintering of Co-W-Ta ternary superalloys: densification mechanism, phase, microstructural and mechanical properties

Inverse design of topological photonic time crystals via deep learning

Photonic time crystals are a new kind of photonic system in modern optical physics, leading to devices with new properties in time. However, so far, it is still a challenge to design photonic time crystals with specific topological states due to the complex relations between time crystal structures and topological properties. Here, we propose a deep-learning-based approach to address this challenge. In a photonic time crystal with time inversion symmetry, each band separated by momentum gaps can have a non-zero quantized Berry phase. We show that the neural network can learn the relationship between time crystal structures and Berry phases, and then determine the crystal structures of photonic time crystals based on given Berry phase properties. Our work shows a new way of applying machine learning to the inverse design of time-varying optical systems and has potential extensions to other fields, such as time-varying phononic devices.

Topological structures and adsorption properties of the [Fe4S4] clusters

The [Fe4S4] compositions are ubiquitous in biological systems as integral parts of the complex catalytic mechanisms as in hydrogenases and nitrogenases. The current reports about [Fe4S4] species are based on the cube-like structure framework. Here, the topological structures, stability and electronic properties of gas phase [Fe4S4]+, [Fe4S4]0 and [Fe4S4]− are analyzed. It is found that ground state structures of these three clusters have similar cubic cages but different symmetries and spin multiplicities. The molecular dynamics simulations demonstrate that the cubic cage remains thermodynamically stable at 700 K. The density of states show that the charge state is the key to affect electronic behaviors of them even under the same structural framework. The molecular orbitals show that the LUMO orbitals are distributed throughout whole structures, showing great delocalized characteristics, especially for the anionic [Fe4S4]−, while the HOMO orbits are mainly localized in Fe-S bonds, which are also confirmed by the electron localization function analyses. After one CO molecule is adsorbed on these clusters, it prefers to locate at the Fe atoms. Moreover, the C–O bond length and vibration frequency of the [Fe4S4]−-CO undergone a significant red shift. Our work shows that the [Fe4S4]− may act as a potential catalyst for activating the C–O bond.

Polarized Raman, infrared and dielectric spectra of lead-free K0.5Na0.5NbO3 piezoelectric system: insights from ab-initio theoretical and experimental studies

The K0.5Na0.5NbO3 (KNN) system has emerged as one of the most promising lead-free piezoelectric over the years. In this work, we perform a comprehensive investigation of electronic structure, lattice dynamics and dielectric properties of room temperature phase of KNN by combining ab-initio DFT based theoretical analysis and experimental characterization. We assign the symmetry labels to KNN vibrational modes and obtain ab-initio polarized Raman spectra, Infrared reflectivity, Born-effective charge tensors, oscillator strengths etc. The KNN ceramic samples are prepared using conventional solid-state method and Raman and UV–Vis diffuse reflectance spectra are obtained. The computed Raman spectrum is found to agree well with the experimental spectrum. In particular, the results suggest that the mode in range ∼840–870 cm−1 reported in the experimental studies is longitudinal optical with A1 symmetry. The Raman mode intensities are calculated for different light polarization set-ups that suggests the observation of different symmetry modes in different polarization set-ups. The electronic structure of KNN is investigated and optical absorption spectrum is obtained. Further, the performances of DFT semi-local, meta-GGA and hybrid exchange-correlations functionals, in the estimation of KNN band gaps are investigated. The KNN bandgap computed using GGA-1/2 and HSE06 hybrid functional schemes are found to be in excellent agreement with the experimental value. The COHP, electron localization function and Bader charge analysis is also performed to deduce the nature of chemical bonding in the KNN. Overall, our study provides several bench-mark important results on KNN that have not been reported so far.

Crystal Field Engineering Inducing Transformation from Narrow Band of Eu3+ to Broadband of Eu2.

The complete transformation from narrow peak emission of Eu3+ to broadband emission of Eu2+ was first realized in La1-xSr2+xAl1-xSixO5:Eu series solutions relying on crystal field engineering and adjustment of synthesis parameters. The original red phosphor La0.97Sr2AlO5:0.03Eu3+peaks at 703 nm originated from 5D0 →7F4 transition of Eu3+ under 395 nm excitation. As the x value regularly increased, Sr2SiO4-type green phosphor La0.17Sr2.8Al0.2Si0.8O5:0.03Eu2+ was synthesized at x = 0.8, which can be efficiently excited by UV/blue light chips. Moreover, when x > 0.975, Sr3SiO5:Eu2+ type broadband orange phosphor Sr2.945Al0.025Si0.975O5:0.03Eu2+ with excellent thermal stability (91.3% peak intensity at 150 °C) was obtained. Variations in the crystal structure, phase, and luminescence properties were studied in detail. We hope this work can provide a reference that solid solution between distinct but structurally related systems is a strategy to explore the possible phosphors for phosphor-converted light-emitting diodes.

Elevated temperature wear and friction performance of WC-CoCr/Mo and WC-Co/NiCr/Mo coated Ti-6Al-4V alloy

The effect of adding Mo to WC-based coatings on the microstructure and dry sliding wear performance at elevated temperatures is investigated. The WC-based coatings are deposited using a high-velocity oxy-fuel process on the titanium-31 substrate. The coating was characterized by microstructure, microhardness, porosity, surface roughness, density, and bond strength. The wear and friction behavior of coatings was evaluated using a ball-on disc tribometer at temperatures of 200, 400, 600, and 800 °C and loads of 20 and 30 N. SEM-EDS and an optical profilometer were utilized to evaluate the wear rate and mechanism. The microhardness and bond strength of WC-CoCr/10%Mo coating is more than that of WC-Co/20%NiCr/10%Mo coatings. The WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coatings exhibited decreasing wear rates up to 600 °C, transitioning to an increase at 800 °C. The oxide phases of CoWO4, WO3, MoO3, CoMoO4, and NiMoO4, formed at 600 °C, aid in reducing the rate of wear and friction coefficient. However, the wear rate slightly increased at 800 °C due to vigorous oxidation and softness of coatings. The friction coefficient of WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coating decreases with increasing temperatures due to the lubricating properties of oxide phases on the worn surface. The WC-CoCr/10%Mo coating demonstrates a lower friction and wear rate than the WC-CoCr and WC-Co/20%NiCr/10%Mo coating. At 200 °C, the predominant wear mechanisms were abrasive and fatigue wear, while at 800 °C, oxidative wear, abrasive wear, and adhesive wear were observed.

Polarized Raman, infrared and dielectric spectra of lead-free K0.5Na0.5NbO3piezoelectric system: insights from ab-initio theoretical and experimental studies.

The K0.5Na0.5NbO3(KNN) system has emerged as one of the most promising lead-free piezoelectric over the years. In this work, we perform a comprehensive investigation of electronic structure, lattice dynamics and dielectric properties of room temperature phase of KNN by combining ab-initio DFT based theoretical analysis and experimental characterization. We assign the symmetry labels to KNN vibrational modes and obtain ab-initio polarized Raman spectra, Infrared (IR) reflectivity, Born-effective charge tensors, oscillator strengths etc. The KNN ceramic samples are prepared using conventional solid-state method and Raman and UV-Vis diffuse reflectance spectra are obtained. The computed Raman spectrum is found to agree well with the experimental spectrum. In particular, the results suggest that the mode in range ~840-870 cm-1 reported in the experimental studies is longitudinal optical (LO) with A_1 symmetry. The Raman mode intensities are calculated for different light polarization set-ups that suggests the observation of different symmetry modes in different polarization set-ups. The electronic structure of KNN is investigated and optical absorption spectrum is obtained. Further, the performances of DFT semi-local, meta-GGA and hybrid exchange-correlations (XC) functionals, in the estimation of KNN band gaps are investigated. The KNN bandgap computed using GGA-1/2 and HSE06 hybrid functional schemes are found to be in excellent agreement with the experimental value. The COHP, electron localization function and Bader charge analysis is also performed to deduce the nature of chemical bonding in the KNN. Overall, our study provides several bench-mark important results on KNN that have not been reported so far.

Mechanical property and frost resistance of phase–change/NanoSiO2 concrete in a low–temperature environment

To study the effect of phase–change materials and nanomaterials as new composite materials on the mechanical properties and frost resistance of concrete, it is beneficial for low–carbon and environmentally friendly buildings to be achieved. The effects of freeze–thaw cycles and different preloading strains were considered. ICT scanning was performed, and the compression performance of composite–modified concrete (CMC) were tested. The internal pore structure and strength indicators of the CMC were analyzed during uniaxial compression. Meanwhile, by conducting uniaxial compression tests on CMC at different temperatures, changes in the mechanical properties during real–time freezing and thawing processes were obtained. The results demonstrated that the fractal dimension grows and the compressive performance of the CMC declines as the number of freeze–thaw cycles and preloading strain increases. The proportion of spheroids in the internal pore shape gradually decreases, whereas the proportions of rods, discs, and blades increases. CMC effectively delays the rise or fall of internal temperature during the freeze–thaw process and reduces its internal structural deterioration. Compared with the freeze–thaw effect, an increase in the preloading strain has a more notable impact on the compressive performance of CMC. A stress–strain constitutive model is proposed for a 10 % microencapsulated phase–change materials and a 1.5 % nanoSiO2 composite–modified concrete (10 mPCMs/1.5 NS CMC), influenced by temperature, through regression analysis. Meanwhile, under low temperatures, the degradation of mechanical properties of 10 mPCMs/1.5 NS CMC and the influence of different preloading strains are considered, leading to the development of stress–strain constitutive models for freeze–thaw cycles and different preloading conditions.

Effect of Copper Chloride on Phase Structure and Properties of Synthesized Materials from Flue Gas Desulfurization Gypsum

This research investigates the influence of crystal modifying agent, copper chloride (CuCl2) (0.3, 0.45, and 0.6 g), on the phase structure and characteristics of materials derived from flue gas desulfurization (FGD) gypsum. The raw material underwent hydrothermal transformation with 0.01 M H2SO4 at 90°C for 1 hour. XRD analysis revealed a notable shift in phase structure from hexagonal calcium sulfate dihydrate (DH) in FGD gypsum to monoclinic calcium sulfate hemihydrate (alpha-HH) up to 91%in the synthesized products, with an increasing CuCl2 content. SEM analysis revealed the elongated whisker-shaped particles (110.70 µm to 207.90 µm) of alpha-HH with higher CuCl2 concentrations. Specifically, when incorporating 0.6 g of CuCl2 in 0.01 M H2SO4 at 90°C, the longest alpha-HH crystals resulted in the cast plaster with the highest flexural strength of approximately 4.92 MPa, demonstrating suitability for applications requiring sufficient mechanical strength. Thermal analysis confirmed the complete conversion of the solid phase to alpha-HH at 1200°C. Additionally, the study revealed that higher CuCl2 content led to shorter setting time. These results suggest potential applications of the present synthesized materials from FGD gypsum in industries such as ceramics casting and dental materials, where precise control over material properties is critical.

Second phase and matrix texture evolution influence mechanical properties of Al-Mg-Al composite plate by HPR with annealing temperature

Annealing treatment can determine the quality of heterogeneous composite plate by regulating the matrix and interface structures and interlayer bonding ability. Al-Mg-Al composite plate was used as an example. Al-Mg-Al composite plate was rolled with 50 % reduction by hard plate rolling. After that, it was annealed at 250 ℃, 300 ℃, 350 ℃ and 400 ℃ for one hour respectively. Through microstructure observation and performance test, the results show that the reaction phases of Al3Mg2 and Al12Mg17 were formed at the interface during annealing treatment. As the temperature continued to climb, yield strength and elongation after fracture of Al-Mg-Al composite plate showed a trend of increasing first and then decreasing, in addition, the tensile strength gradually decreased. As temperature reached 300 °C, its performance reached the best, the tear strength increased to 0.367 KN, and yield strength and elongation reached 172 MPa and 14.5 %, respectively. The study showed that although annealing temperature didn't change types of texture configuration of magnesium alloy, it affected the grain growth, resulting in the change of base surface texture and the overall performance of heterogeneous composite plate. This research provides a theoretical basis for precise regulation of microstructure and comprehensive performance of heterogeneous composite plate by annealing treatment.

Effect of Copper Chloride on Phase Structure and Properties of Synthesized Materials from Flue Gas Desulfurization Gypsum

Effect of Copper Chloride on Phase Structure and Properties of Synthesized Materials from Flue Gas Desulfurization Gypsum

Dielectric anisotropy in self-assembling MXene-based lyotropic nematic compounds

The formation of a lyotropic liquid crystal phase at the level of MXene-based aqueous dispersions due to the self-assembling capacity of these two-dimensional (2D) materials has been previously successfully reported. However, the influence of electrical external factors has been less studied in spite of the fact that understanding the electrical behaviour of 2D-based liquid crystal compounds is vital for fostering the development of new innovative applications. Consequently, within this paper, we report an in-depth evaluation of the dielectric properties of liquid crystalline phases in Ti3C2 MXene aqueous dispersions. The dependence on the low voltage of planar ε⊥′ to homeotropic ε∥′ orientational transition is emphasized and discussed, while the influence of the electric field frequency at the level of dielectric anisotropy is assessed in respect to various concentrations of MXene flakes within the same 2D-based compounds. Nonetheless, dielectric spectroscopy highlights the biphasic nature (containing both nematic and isotropic phases) of the studied aqueous Ti3C2 MXene inks visible up to 20% MXene. Above this concentration, the existence of a pure nematic phase in the dispersion of highMXene concentration (>20 wt%) was detected based on the evaluation of dielectric permittivity against various voltage values.

Dataset for quantum-mechanical exploration of conformers and solvent effects in large drug-like molecules

We here introduce the Aquamarine (AQM) dataset, an extensive quantum-mechanical (QM) dataset that contains the structural and electronic information of 59,783 low-and high-energy conformers of 1,653 molecules with a total number of atoms ranging from 2 to 92 (mean: 50.9), and containing up to 54 (mean: 28.2) non-hydrogen atoms. To gain insights into the solvent effects as well as collective dispersion interactions for drug-like molecules, we have performed QM calculations supplemented with a treatment of many-body dispersion (MBD) interactions of structures and properties in the gas phase and implicit water. Thus, AQM contains over 40 global and local physicochemical properties (including ground-state and response properties) per conformer computed at the tightly converged PBE0+MBD level of theory for gas-phase molecules, whereas PBE0+MBD with the modified Poisson-Boltzmann (MPB) model of water was used for solvated molecules. By addressing both molecule-solvent and dispersion interactions, AQM dataset can serve as a challenging benchmark for state-of-the-art machine learning methods for property modeling and de novo generation of large (solvated) molecules with pharmaceutical and biological relevance.

Structural, optical, and gas sensing characteristics of synthesized environmentally friendly ZnO-ZnAl2O4 nanocomposites

In this study, we synthesized ZnO-ZnAl2O4 composites from orange peel extract by using an environmentally friendly approach. ZnO-ZnAl2O4 composites with different Al content, namely 30, 40, 50, 60, and 70 at%, were successfully synthesized, and they were characterized in detail using advanced techniques to study their structures, phases, morphologies, and electrical and optical properties. Gas sensing measurements for H2S gas showed that the sensor with 70 at% Al had the best response at 350 °C along with long-term stability. We attribute this high response to the high specific surface area (48.8 m2·g−1), the formation of ZnO-ZnO homojunctions and ZnO-ZnAl2O4 heterojunctions, and the high intrinsic sensing properties of the ZnO phase. This study is expected to contribute to the development of green approaches for the synthesis of environmentally friendly gas sensing materials.