Phase Transition Characteristics Research Articles

Study on the phase transition characteristics of nano-hydrated salts based on molecular dynamics simulations

Hydrated salts possess great competitiveness in terms of enhancing utilization efficiency of heat due to large densities of heat storage and low costs. However, the existence of supercooling degree is the common phenomenon for hydrated salts, which might restrict the application prospects in partial fields. This work focuses on hydrated salts with relatively larger latent heats, namely Na2CO3·10H2O and Na2HPO4·14H2O in the absence and presence of SiO2 as well as eutectic hydrated salt prepared with 40 wt% Na2CO3·10H2O and 60 wt% Na2HPO4·12H2O. Their melting/solidification temperatures were determined and the supercooling behavior was analyzed based on molecular dynamics simulations. The simulation results of melting/solidification temperatures present small deviations of 0.17–3.24 ℃ in comparison with experimental data. Additionally, the aggregation phenomenon among salt ions and dispersion phenomena among water molecules and between water molecules and salt ions for supercooled liquid hydrated salts are revealed, which are attributed to stronger electrostatic interactions and weaker van der Waals interactions as well as lower binding energies. Moreover, SiO2 not only lowers melting temperatures due to its higher thermal conductivity than hydrated salts and the existence of micro-convection, but affects solidification behavior of hydrated salts. The different influences of SiO2 on solidification temperatures of Na2HPO4·14H2O and Na2CO3·10H2O were associated with dispersion degree between water molecules and salt ions around SiO2, which would be attributed to different strengths of interaction forces between SiO2 and salt ions. On these bases, this work provides new perspectives for clarifying phase change characteristics of nano-hydrated salts.

Characteristics of Solid Mineral Phase Transitions During Sulfuric Acid Production from Gaseous-Sulphur-Reduced Gypsum

The acid co-production of cement is a prominent research focus for the large-scale, high-value utilization of phosphogypsum in the context of dual-carbon strategies. This paper builds on extensive research conducted by its authors on the co-production of sulphoaluminate cement clinker through acid production from gaseous-sulphur-reduced phosphogypsum. The solid mineral phase transformations occurring in the kiln during this process are systematically studied, and the effects of various calcination regimes (temperature, time, and atmosphere) on the evolution of clinker mineral phases are elucidated. This paper provides basic data support for the gas-sulfur-reduced phosphogypsum-acid cogeneration of sulfoaluminate cement clinker processes, and promotes the realization of the large-scale high-value utilization of phosphogypsum resources. The generation of the clinker mineral phase anhydrous calcium sulphoaluminate (C4A3S̅) begins at 1100 °C. Increasing the calcination temperature and extending the calcination time promote C4A3S̅ formation. However, when the calcination temperature exceeds 1350 °C, C4A3S̅ decomposes, leading to the formation of low-activity C2AS. In a CO atmosphere, the main mineral phases in the clinker transform into C2AS and 12CaO·7Al2O3, owing to the decomposition of CaSO4, which inhibits C4A3S̅ formation. At calcination temperatures exceeding 1300 °C, a significant amount of C2AS appears in the calcined material, and 12CaO·7Al2O3 begins to form.

Mechanism of protofibril formation in aqueous collagen solutions

The shear viscosity of aqueous collagen solutions was experimentally investigated over the temperature range of 303–353 K and collagen concentrations of 1–7 wt. %. A structural phase transition was observed at ∼315 K, corresponding to the onset of protofibril formation. It is shown that below this temperature, protofibrils containing both ordered and disordered segments are formed, with the proportion of ordered segments increasing as the temperature decreases, reaching ∼30% at 303 K. An analysis of the temperature dependence of the order parameter for the structural transition in the water–collagen system suggests that this transition exhibits characteristics of a second-order phase transition.

Machine learning in additive manufacturing——NiTi alloy’s transformation behavior

The laser powder bed fused NiTi alloys (LPBF-NiTi) demonstrate shape memory functionality and superelasticity as a result of their distinctive phase transition characteristics. Nevertheless, achieving precise control and regulation of the phase transition temperature poses a challenge, influenced by factors like powder composition and process parameter. In this study, a feature screening strategy and machine learning (ML) method were employed to predict and regulate the phase transition temperature of LPBF-NiTi alloy, offering a more efficient and cost-effective alternative to traditional experimental methods of regulation and control. Specifically, accuracy analysis was performed on LPBF-NiTi phase transition datasets with varying compositions and process conditions utilizing generalized regression neural network (GRNN), and other methods. The findings indicate that the interpretable features extracted through the selection strategy outlined in this study when combined with the GRNN model, demonstrate a high level of prediction accuracy (R2 = 0.97). To investigate the accuracy of the model, this study utilized various process parameters to fabricate NiTi alloys with different compositions from Ni50.8Ti49.2 alloy powder. Using this model, the study identified a novel, larger window of optimal LPBF processing that allows for controllable complex phase transitions.

The Impact of the Final Sintering Temperature on the Microstructure and Dielectric Properties of Ba0.75Ca0.25TiO3 Perovskite Ceramics.

Ba0.75Ca0.25TiO3 ceramics were successfully synthesized by a simple solid-state reaction method. This study examined the influence of sintering temperature on the structure, microstructure, dielectric properties and electrical behavior of the material. The XRD analysis reveals that the tetragonal phase (P4mm) is dominant in all the synthesized materials, with those sintered at T = 1400 °C and T = 1450 °C being single-phase, while others exhibit a minor orthorhombic phase (Pbnm). Higher sintering temperatures promoted better grain boundary formation and larger grain sizes. The electric permittivity increased with temperature up to T = 1400 °C, followed by a sharp decline at T = 1450 °C. Additionally, the Curie temperature decreased with increasing sintering temperature, indicating changes in phase transition characteristics. Thermal analysis showed that higher sintering temperatures led to sharper heat capacity peaks, while pyroelectric and thermally stimulated depolarization currents were maximized at T = 1400 °C due to oxygen vacancies. These findings highlight the significant impact of sintering temperature on the material's structural and functional properties.

Tailoring the microstructure, phase transition characteristics and one-way shape memory effect of Ni-Mn-Ga alloys by dual treatment of annealing and directional solidification

Improving both shape memory effect (SME) and mechanical properties is a major challenge of Ni-Mn-Ga high temperature shape memory alloy. In this work, the Ni57Mn25Ga18 alloy system with the coexistence of martensite phase and γ phase at room temperature is selected. A regulation strategy involving annealing and directional solidification (DS) is adopted to control the phase transition characteristics and crystallographic texture of the alloy. Annealing treatment can reduce the elastic strain energy in the alloy and reduce the macroscopic energy barrier between the martensite phase and the austenite phase. As a result, the martensitic phase transition temperatures of the alloy shift towards the high-temperature zone, and the transition width decreases. DS can eliminate transverse grain boundaries and reduce orientation difference. By this composite method, the one-way shape memory effect (OWSME) and mechanical properties are improved, the strain generated by OWSME and the fracture stress of the annealed DS alloy reaches 4.62 % and 1922 MPa, respectively. In annealed DS samples, stacking faults are accumulated in martensite phases and the atomic arrangement of the γ phases becomes ordered, which can provide many slip systems, they are account for the enhanced mechanical properties. The columnar grains obtained by DS have the consistent deformation direction same and small internal stress, thus their deformation is easy to recover. The martensitic texture, particularly with the (001)NM orientation, is parallel to the DS direction and conducive to the OWSME.

Experimental study on the quasi-static tensile mechanical response of PTFE from 77 K to 293 K

PTFE’s exceptional low-temperature resistance makes it an ideal material for cryogenic aerospace fuel seals. However, the current understanding of its mechanical behaviors at low temperatures remains limited, posing potential design vulnerabilities. This study investigates the quasi-static mechanical properties of PTFE over a temperature range from 77 K to room temperature, with a particular focus on the effects of temperature and strain rate, which are key variables in sealing applications. The experimental conditions are categorized into ambient temperature (293 K), conventional low temperatures (233 K–293 K), and cryogenic temperatures (77 K–223 K). Testing was conducted at crosshead speeds of 1, 10, and 100 mm/min to evaluate their influence. The results reveal significant phase transition characteristics in PTFE’s low-temperature mechanical properties, with the effects of phase transitions far outweighing those of strain rate, leading to dramatic changes in the stress response, from elasticity through plasticity to fracture. Further analysis indicates that these effects are concentrated around the transition state temperature zone, with slower changes observed at other temperatures. This study highlights the critical importance of considering phase transitions in the low-temperature design of PTFE structures.

Phase-Transition-Promoted Interfacial Anchoring of Sulfide Solid Electrolyte Membranes for High-Performance All-Solid-State Lithium Battery.

Solvent-free manufacturing is crucial for fabricating high-performance sulfide-electrolyte-based all-solid-state lithium batteries (ASSLBs), with advantages including side reaction inhibition, less contamination, and practical scalability. However, the fabricated sulfide electrolytes commonly suffer from brittleness, limited ion transport, and unsatisfactory interfacial stability due to the uncontrolled dispersion of the sulfide particles within the polymer binder matrix. Herein, a "solid-to-liquid" phase transition strategy is reported to fabricate flexible Li6PS5Cl (LPSCl) electrolytes. The polycaprolactone (PCL)-based binder (PLI) with phase-transition characteristics fills the gap of LPSCl particles and tightly grafts on the particle surface via ion-dipole interaction, bringing a thin and compact electrolyte membrane (80µm). The simultaneously high Li-ion conducting and electron insulating nature of PLI binder facilitates Li-ion transport and ensures good interfacial stability between electrolyte and anode. Consequently, the sulfide electrolyte membrane exhibits high ionic conductivity (8.5×10-4 S cm-1), enabling symmetric and full cells with 10 and 2.5 times longer cycling life compared with that of the cells with pristine LPSCl electrolyte, respectively. The demonstrated strategy is versatile and can be extended to ethylene vinyl acetate copolymer (EVA) that also brings enhanced electrochemical performance. The thin sulfide electrolyte with high interfacial stability potentially facilitates dendrite-free ASSLBs with high energy density.

A Tunable Transparent Graphene Absorber with Multifrequency Resonance

AbstractThe demand for multinarrowband absorber has attracted increasing interest among researchers in recent years. However, integrating multifrequency absorption, tunability, and high optical transparency into an absorber remains a crucial challenge. In this study, a multiband, tunable, and transparent microwave meta‐absorber is theoretically proposed and experimentally demonstrated. This meta‐absorber is composed of resonant patterns made from graphene and indium tin oxide (ITO), placed on a substrate of lithium niobate (LN). By introducing P‐type doping to reduce the resistance of monolayer graphene to around 300 Ω, the impedance matching of the absorber is promoted, consequently manifesting ten absorption points within 40 GHz. The electric field distribution analysis and an equivalent circuit model are employed to elucidate the physical mechanisms of the multiband absorber. Additionally, the lithium niobate dielectric layer possesses a substantial dielectric constant and exhibits phase transition characteristics with temperature changes. When the temperature increases to 250 °C, a comprehensive tuning range of more than 5.49 GHz within 40 GHz range is realized. The maximum tuning range for a single frequency point is 1.33 GHz. With the broadening of the band, the meta‐absorber can provide multiple tunable ranges, making it more favorable for practical applications in optical modulator and sensor.

Study on water hammer phase transition characteristics of dense/liquid phase CO2 pipeline

Under water hammer conditions, dense/liquid phase CO2 pipelines are prone to enter the phase equilibrium zone due to significant pressure fluctuations, further disrupting flow stability. At present, the research on the sudden changes in physical properties and pressure wave transmission characteristics caused by CO2 phase transition during water hammer transient process is not clear. This article uses experiments to screen the state equation suitable for CO2 phase characteristic calculation. Based on this, the characteristic line method is used to solve the one-dimensional pipeline water hammer flow process. When the water hammer pressure is lower than the saturation pressure, the corresponding gas phase fraction is solved using the isentropic principle. The results indicate that a phase transition occurs under water hammer conditions when the operating temperature is 280–300 K and the operating pressure is 0.59 %–4.55 % higher than the saturation pressure. When a phase transition occurs, for the valve front, 1.33 % gas generation will increase the pressure wave velocity by 1.67 %, and for the valve rear, 0.86 % gas generation will increase the pressure wave velocity by 0.61 %. This study provides a basis for the safe and stable operation of CO2 pipelines.

Fluctuation-driven morphological patterning: An unconventional approach to morphogenesis

Recent experimental investigations into regeneration revealed a remarkable phenomenon: the morphological transformation of a tissue fragment from the incipient spherical configuration to a tubelike structure—the hallmark of a mature —has the dynamical characteristics of a first-order phase transition, with calcium field fluctuations within the tissue playing an essential role. This morphological transition was shown to be generated by activation over a barrier within an effective morphological potential that underlies morphogenesis. Inspired by this intriguing insight, we propose an unconventional mechanism where stochastic fluctuations drive the emergence of morphological patterns. Thus, the inherent fluctuations determine the nature of the dynamics and are not incidental noise in the background of the otherwise deterministic dynamics. Instead, they play an important role as a driving force that defines the attributes of the pattern formation dynamics and the nature of the transition itself. Here, we present a simple model that captures the essence of this mechanism for morphological pattern formation. Specifically, we consider a one-dimensional tissue arranged as a closed contour embedded in a two-dimensional space, where the local curvature of the contour is coupled to a non-negative scalar field. An effective temperature parameter regulates the strength of the fluctuations in the system. The tissue exhibits fluctuations near a circular shape at sufficiently low coupling strengths, but as the coupling strength exceeds some critical value, the circular state becomes unstable. The nature of the transition to the new state, namely whether it is a first-order-like or second-order-like transition, depends on the effective temperature and the effective cutoff on the wavelength of the spatial variations in the system. The former sets the level of noise, while the latter determines the height of the potential barrier between the initial circular state and the final deformed state of the tissue. It is also found that entropic barriers separate various metastable states of the system. Published by the American Physical Society 2024

A novel measurement method of thermal performances for an improved thermal storage concrete with microencapsulated phase change materials

Integrating micro-encapsulated phase change materials into concrete member is among the effective strategies to optimize its thermal properties. However, the addition of microencapsulated phase change materials changes the meso-structure and heat storage of concrete, which gives rise to the difference in measurement method of thermal properties between common concrete and concrete with micro-encapsulated phase change materials. The primary aim of this paper is to develop an experimental model that takes into consideration both the structure and phase-transition characteristics of concrete with micro-encapsulated phase change material. The developed experimental model consists of three Modules that form different thermal boundary conditions to test specific heat capacity, latent heat, thermal conductivity, and heat attenuation. To investigate the effect of environment temperature on the thermal properties, three groups of concrete slabs with different micro-encapsulated phase change material dosage were fabricated and tested. Results shown that the environment temperature has little effect on both specific heat capacity and thermal conductivity of concrete without micro-encapsulated phase change material, while significantly affects that of concrete containing micro-encapsulated phase change material. The specific heat capacity of concrete with 5.0 % micro-encapsulated phase change material was 1.273 J/g °C at around 28 °C, yet 0.958 J/g °C at around 18 °C.The thermal conductivity of concrete with micro-encapsulated phase change material was affected by both paraffin state and dosage. The thermal conductivity of the concrete with 5.0 % micro-encapsulated phase change material reduced by 8.44 % when the state of paraffin changed from solid to liquid. The latent heat of concrete with micro-encapsulated phase change material were enhanced. Additionally, the heat attenuation ascends by 32.34 % when the MPCM dosage increase from 0.0 % to 5.0 %.

Mechanically adaptive and deployable intracortical probes enable long-term neural electrophysiological recordings

Flexible intracortical probes offer important opportunities for stable neural interfaces by reducing chronic immune responses, but their advances usually come with challenges of difficult implantation and limited recording span. Here, we reported a mechanically adaptive and deployable intracortical probe, which features a foldable fishbone-like structural design with branching electrodes on a temperature-responsive shape memory polymer (SMP) substrate. Leveraging the temperature-triggered soft-rigid phase transition and shape memory characteristic of SMP, this probe design enables direct insertion into brain tissue with minimal footprint in a folded configuration while automatically softening to reduce mechanical mismatches with brain tissue and deploying electrodes to a broader recording span under physiological conditions. Experimental and numerical studies on the material softening and structural folding-deploying behaviors provide insights into the design, fabrication, and operation of the intracortical probes. The chronically implanted neural probe in the rat cortex demonstrates that the proposed neural probe can reliably detect and track individual units for months with stable impedance and signal amplitude during long-term implantation. The work provides a tool for stable neural activity recording and creates engineering opportunities in basic neuroscience and clinical applications.

Phase-Engineered MoSe2/CeO2 Composites for Room-Temperature Gas Sensing with a Drastic Discrimination of NH3 and TEA Gases.

Detecting and distinguishing between hazardous gases with similar odors by using conventional sensor technology for safeguarding human health and ensuring food safety are significant challenges. Bulky, costly, and power-hungry devices, such as that used for gas chromatography-mass spectrometry (GC-MS), are widely employed for gas sensing. Using a single chemiresistive semiconductor or electric nose (e-nose) gas sensor to achieve this objective is difficult, mainly because of its selectivity issue. Thus, there is a need to develop new materials with tunable and versatile sensing characteristics. Phase engineering of two-dimensional materials to better utilize their physiochemical properties has attracted considerable attention. Here, we show that MoSe2 phase-transition/CeO2 composites can be effectively used to distinguish ammonia (NH3) and triethylamine (TEA) at room temperature. The phase transition of nanocomposite samples from semimetallic (1T) to semiconducting (2H) prepared at different synthesis temperatures is confirmed via X-ray photoelectron spectroscopy (XPS). A composite sensor in which the 2H phase of MoSe2 is predominant lacks discrimination capability and is less responsive to NH3 and TEA. An MoSe2/CeO2 composite sensor with a higher 1T phase content exhibits high selectivity for NH3, whereas one with a higher 2H phase content (2H > 1T) shows more selective behavior toward TEA. For example, for 50% relative humidity, the MoSe2/CeO2 sensor's signal changes from the baseline by 45% and 58% for 1 ppm of NH3 and TEA, respectively, indicating a low limit of detection (LOD) of 70 and 160 ppb, respectively. The composites' superior sensing characteristics are mainly attributed to their large specific surface area, their numerous active sites, presence of defects, and the n-n type heterojunction between MoSe2 and CeO2. The sensing mechanism is elucidated using Raman spectroscopy, XPS, and GC-MS results. Their phase-transition characteristics render MoSe2/CeO2 sensors promising for use in distributed, low-cost, and room-temperature sensor networks, and they offer new opportunities for the development of integrated advanced smart sensing technologies for environmental and healthcare.

Fluctuation effects in superconducting nanowires under electric field

This study applies the time-dependent Ginzburg–Landau (TDGL) theory with thermal noise to analyze the thermoelectric and transport properties of superconducting Sn nanowires, focusing on the thermopower (αxx) and the phase transition characteristics in the S-shaped J-E curves. We observe significant contributions from superconducting Cooper pairs, which remain nonzero above the critical temperature (Tc), indicating residual superconductivity due to strong thermal fluctuations. The S-like shape in the J-E curves is attributed to a dynamical instability transition temperature (T∗) at approximately 2.9 K, where thermal fluctuations dominate. Furthermore, we compare the resistance in the linear response to experimental data for Sn nanowires both below and above Tc. Below Tc, the resistance sharply decreases, reflecting the robust superconducting state, while above Tc, it increases, aligning with normal state behavior. In nonlinear response case, our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations and the electrical conductivity in superconducting nanowires. The findings provide critical insights into the thermoelectric behavior and phase transitions in Sn nanowires, highlighting the importance of Cooper pair dynamics in shaping the transport properties of one-dimensional superconductors. This understanding is essential for the development of advanced nanoelectronic devices leveraging these unique superconducting properties.

Real-Space Imaging of Intrinsic Symmetry-Breaking Spin Textures in a Kagome Lattice.

The electronic orders in kagome materials have emerged as a fertile platform for studying exotic quantum states, and their intertwining with the unique kagome lattice geometry remains elusive. While various unconventional charge orders with broken symmetry is observed, the influence of kagome symmetry on magnetic order has so far not been directly observed. Here, using a high-resolution magnetic force microscopy, it is, for the first time, observed a new lattice form of noncollinear spin textures in the kagome ferromagnet in zero magnetic field. Under the influence of the sixfold rotational symmetry of the kagome lattice, the spin textures are hexagonal in shape and can further form a honeycomb lattice structure. Subsequent thermal cycling measurements reveal that these spin textures transform into a non-uniform in-plane ferromagnetic ground state at low temperatures and can fully rebuild at elevated temperatures, showing a strong second-order phase transition feature. Moreover, some out-of-plane magnetic moments persist at low temperatures, supporting the Kane-Mele scenario in explaining the emergence of the Dirac gap. The observations establish that the electronic properties, including both charge and spin orders, are strongly coupled with the kagome lattices.

Magnetic properties and large low-field magnetocaloric effect of RFe2Si2 (R = Ho, Tm) compounds

Nowadays, magnetic refrigerant technology has drawn much attention for its environmental friendliness. Those magnetic materials possessing giant low-field magnetocaloric effect (MCE) performance are of great importance for practical applications, especially at low temperatures. Herein, we present a detailed study on polycrystalline magnetocaloric compounds HoFe2Si2 and TmFe2Si2. HoFe2Si2 exhibits a transition from antiferromagnetic to paramagnetic phase at 2.2 K, while no long-range magnetic ordering is observed in TmFe2Si2 even temperature down to 2 K. For both compounds, they showed large low-field magnetic entropy change (−ΔSM) with the peak values of 10.6 and 7.9 J kg−1 K−1 under field change of 0–2 T for HoFe2Si2 and TmFe2Si2, respectively, which is comparable or even larger than some low-temperature magnetocaloric materials. In addition, the characteristic of second-order magnetic transitions of both compounds were confirmed on basis of Arrott plots and mean-field theory criterion. The low magnetic ordering temperatures, large low-field MCE performance along with the feature of second order phase transition for HoFe2Si2 and TmFe2Si2 indicate that both compounds are promising candidate for magnetic refrigerant materials at liquid helium temperature.

Solid–fluid phase transition characteristics of loess and its drag reduction mechanism

Solid–fluid phase transition characteristics of loess and its drag reduction mechanism

Cascaded Heteroporous Nanocomposites for Thermo-Adaptive Passive Radiation Cooling.

Passive radiative cooling is a promising technology for heat dissipation that does not consume energy. However, current radiative cooling materials can only exhibit subambient cooling under atmospheric conditions and struggle to process specific heat accumulation. Thus, a passive thermal regulation mechanism adapted to wide-temperature-range applications is required to match device heating systems. Herein, a heteroporous nanocomposite film (HENF) with thermo-adaptive radiation cooling performance is reported. Compared to conventional porous cooling films with limited scattering efficiencies, the HENFs with multistage scattering have a strong emissivity of 96.5% (8-13µm) and a high reflectivity of 97.3% (0.3-2.5µm), resulting in an ultrahigh cooling power of 114Wm-2. In such HENFs, theoretical analyses have confirmed the spectrum management superiority of the heteroporous unit in terms of the scattering efficiency strength, with their cascading effect enhancing the overall film-cooling efficiency. The high mechanical performance, phase-transition features, and environmental adaptive properties of HENFs are also exhibited. Importantly, HENFs synergistically couple thermal dissipation and absorption to effectively process heat accumulation and counteract thermal shock in heating devices. It is anticipated that thermo-adaptive HENFs will act as a promising platform for device surface thermal regulation over a wide temperature range.

Revealing failure law of single-track traffic-loaded concrete airport pavement from a thermodynamic perspective

ABSTRACT With the growth of global air traffic and the popularity of large aircraft, the design and life prediction of airport pavements have received increasing attention from scholars. However, concrete airport pavement evaluations based on cracking patterns are often uncertain. A thermodynamic-based failure analysis of the FAA Phase 4 Construction Cycle 8 (CC8) strength and fatigue traffic test is conducted in this work to investigate the failure laws of airport concrete pavements. First, this work equates concrete pavement failure to a phase transition. It converts strain data from full-scale traffic tests into state variables. Based on the Wilson theory definition of phase transition, network-free renormalisation is applied to reveal the concrete slab stressing state evolution and phase transition features. The clustering algorithm that utilises the attractor effect of phase transition points determines characteristic points. In summary, this work applies network-free renormalisation and clustering algorithms to reveal robust concrete pavement failure points, which can provide a reference for airport pavement design, assessment, and failure warning. Furthermore, this work further validates the stressing state theory and network-free renormalisation under high-speed time-varying conditions.