Solid Phase Transition Research Articles

Temperature-sensitive intelligent gel to prevent coal spontaneous combustion: Large-scale simulation fire extinguishing experimental study

Coal spontaneous combustion seriously endangers mine safety production. In this study, a temperature-sensitive intelligent gel was synthesised from methylcellulose (MC), polyethene glycol (PEG) and sodium chloride (NaCl). The flow characteristics of temperature-sensitive intelligent gel (abbreviated as TSIG) under different conditions were analyzed by viscosity test. An infrared spectrometer also analyzed the microscopic flame retardant mechanism of temperature-sensitive intelligent gel. A large-scale simulation fire extinguishing test bench was designed at the coal mine site to analyze the flame retardant effect of the temperature-sensitive intelligent gel on coal oxidation reaction at different injection temperatures. The results show that the temperature-sensitive intelligent gel undergoes a liquid–solid phase transition at a temperature higher than 60 °C. When MC: PEG: NaCl = 1: 6: 5, the temperature-sensitive intelligent gel showed the best flow characteristics. The large-scale simulation fire extinguishing experiments show that the CO concentration is significantly reduced after the temperature-sensitive intelligent gel is injected at the coal temperature of 300–900 ℃, and both show excellent fire extinguishing effects. The addition of temperature-sensitive intelligent gel can inhibit the number of free radicals in the process of coal oxidation, block the chain reaction of coal spontaneous combustion, and comprehensively inhibit the process of coal spontaneous combustion. The research results provided theoretical support for the application of temperature-sensitive intelligent gel in coal spontaneous combustion areas. Additionally, they guided the design of temperature-sensitive intelligent gel to prevent coal spontaneous combustion technology.

Modeling spider silk supercontraction as a hydration-driven solid-solid phase transition

Spider silks have attracted significant interest due to their exceptional mechanical properties, which include a unique combination of high strength, ultimate strain, and toughness. A notable characteristic of spider silk, still debated from both mechanical and functional viewpoints, is supercontraction–a pronounced contraction of up to half its original length when an unconstrained silk thread is exposed to a wet environment. We propose a predictive model for the hygro-thermo-mechanical behavior of spider silks, conceptualizing this phenomenon as a solid–solid phase transition, similar to the glass transition in rubber, but driven by humidity. As wetting increases, the system undergoes a transition, at the network scale, from a hard, highly crystalline, dry state–where the material behavior is governed by stiff chains elongated along the fiber axis–to a soft, amorphous, wet state, regulated by a rubber-like response. We model these states using a two-well free energy function dependent on molecular stretch, with transition energy modulated by humidity. Based on the methods of Statistical Mechanics, we deduce that supercontraction can be interpreted as a solid–solid phase transition. We elucidate the important role of thermal fluctuations. In particular, the decrease of the critical humidity needed for supercontraction as temperature grows results as an effect of entropic stabilization of the softer rubbery phase. Our model quantitatively predicts the observed experimental behavior, capturing the temperature dependence of humidity-induced supercontraction effects and related cooperative properties.

Computational integration and experimental validation of a two-length scale model for accurate prediction of steels’ plastic behavior during phase transformation

Transformation plasticity, essential during solid–solid phase transitions, significantly impacts industrial processes like welding and quenching. Accurately simulating these procedures necessitates understanding thermal, metallurgical, and mechanical effects. Leblond et al.’s model offers a foundation, but refinement for mixed isotropic/kinematic hardening is crucial. We enhance this model by introducing characteristic length scales through nonlocal variables, illuminating plastic deformation mechanisms in both phases. Our work includes numerical implementation within a finite element analysis framework and practical applications to phase transformation scenarios involving A.508 cl. 3 and A533 low-alloy steels. Results affirm model robustness and efficiency in predicting phase transformation phenomena, benefiting industrial applications.

Prediction of melting and solid phase transitions temperatures and enthalpies for triacylglycerols using artificial neural networks

Triacylglycerols (TAG) are the main components of vegetable oils and any attempt to simulate vegetable oils processes will demand knowledge of their properties. However, experimental values are scarce, considering that several TAG in their pure forms are unavailable or too expensive for experimental measurements. On the other hand, correlating physical properties with TAG molecular structure is not simple. TAG is a molecule composed of 3 fatty acids (FA) esterified to a glycerol (GL) backbone, making properties dependent on carbon number (CN) of each FA, number of unsaturations (UN) of each FA, and position of the FA in the GL backbone. Few models are available in literature for prediction of TAG melting properties, with a special attention to melting temperature (Tfus) and enthalpy (ΔHfus) and solid-solid transition properties of the TAG polymorphic forms. Wesdorp's, Moorthy's et al. and Zeberg-Mikkelsen and Stenby's works present models based on the Group-Contribution theory nowadays used, despite some flaws, particularly considering the polymorphic transitions. Therefore, this work was aimed at evaluating Artificial Neural Network (ANN) models for prediction of TAG's Tfus and ΔHfus (β-form) as well as temperature and enthalpy transitions of molecule polymorphic forms (α and β’). Database was composed of temperature and enthalpy experimental data from literature. For each TAG, 7 input data were provided: total CN, as well as CN and UN at sn-1, 2 and 3 TAG position. The Multilayer Perceptron Feed Forward (MPL) model was used, and the topology was evaluated for number of hidden layers (HL), number of neurons (NN) and activation function at each hidden layer, and convergence algorithm. Number of HL and NN was screened by using a Central Composite Rotatable Design (CCRD). Models were further evaluated by Explainable Artificial Intelligence (XAI) and feature evaluation strategies. Architectures showed a significant higher accuracy for calculation and prediction of TAG's melting properties of the 3 polymorphic forms, with R2 higher to 0.91 for all databases when compared to literatures’ models (excepted for the prediction of the melting temperature of the β form, where Wesdorp's model presented a better predictive ability, despite great similarity). Good results were probably related to the well-defined physicochemical relationship between input (molecular structure descriptors) and output (melting properties), that could be described by XAI evaluation. This is an important advantage considering the improvement of the performance of process and products design including TAG molecules.

Reduction of the residual warpage of fused deposition modeling by negative thermal expansion filler

We investigated the suppression of residual warpage using a negative thermal expansion (NTE) material filler, Zn1.6Mg0.4P2O7. To focus on the effect of thermal expansion on residual warpage, we used acrylonitrile-butadiene-styrene, which is an amorphous polymer with a small volume change around the liquid–solid phase transition, as the matrix. Composite pellets were prepared using a kneader, and filaments were produced for fused deposition modeling (FDM) using an extruder. We fabricated a bar-like test piece using a standard FDM machine and measured the warpage deformation using 3D scanning. The experimental results were supported by the finite element method. We also compared similarly sized SiO2 powders to discuss the advantages of NTE over conventional fillers. The warpage of a 100 mm x 5 mm x 2 mm bar-like test piece was reduced by approximately 75% by introducing Zn1.6Mg0.4P2O7 at 40 vol%. The effect of Zn1.6Mg0.4P2O7 at 30 vol% is similar to that of a conventional SiO2 filler at 40 vol%. Reducing the residual deformation through fillers would reduce energy consumption and simplify the device by avoiding build stage and chamber heating.

A study on microstructure evolution of MCrAlY coatings after thermal aging in Te environment

The effects of thermal exposure on tellurium (Te) diffusion behavior in MCrAlY coatings were investigated at 800 °C in Te vapor. The results showed that the diffusion depth of Te in MCrAlY coatings gradually increased with the exposure time, and the dense Cr3Te4 layer formed on the coating surface in the initial stage was no longer continuous, especially under aging conditions with higher Te concentration. The high Cr content of the coating promoted the solid phase transition of the surface reaction product from Cr3Te4 to Cr7Te8, and resulting in the formation of large α-Cr phase either within or beneath the reaction layer during long aging processes. As a result of this phase transition, excess Te atoms were released from Cr3Te4 and continued to diffuse into the coating. Te did not exhibit obvious intergranular diffusion characteristics within the coating. When it encountered Y, it was captured by Y and formed a YTe phase. After aging for 3000 h, Te was distributed throughout the coating, and numerous voids were formed at the interface between the coating and the substrate. These two factors deteriorated the plasticity and adhesion of the coating. Results from molten salt corrosion tests indicated that the high content of Cr and Al in the coating, as well as high densities of grain boundaries providing diffusion pathways, reduced the corrosion resistance of the coating to molten salt.

Interrogating the Solid–Solid Phase Transition Behavior of a Molecular Crystal with a Diverse Range of Solid-State Analytical Techniques and Computational Predictions

Interrogating the Solid–Solid Phase Transition Behavior of a Molecular Crystal with a Diverse Range of Solid-State Analytical Techniques and Computational Predictions

Analysis of shear localization in viscoplastic solids with pressure-sensitive structural transformations

Localization, in the form of adiabatic shear, is analyzed in viscoplastic solids that may undergo structural transformation driven by pressure, shear stress, temperature, and magnetic field. As pertinent to polycrystalline metals, transformations may include solid–solid phase transitions, twinning, and dynamic recrystallization. A finite-strain constitutive framework for isotropic metals is used to solve a boundary value problem involving simple shearing with superposed hydrostatic pressure and constant external magnetic field. Three-dimensional theory is reduced to a formulation simple enough to facilitate analysis without advanced numerical methods, yet sophisticated enough to maintain the salient physics. Ranges of constitutive parameters (e.g., strain hardening, strain-rate sensitivity, thermal softening, and strain-driven structure transformation limits influenced by pressure and magnetic field) are obtained for which localization to infinite shear strain is possible. Motivated by experimental and theoretical studies suggesting a non-negligible role of shear on phase transformations in iron (Fe), the model is used to understand influences of pressure and phase transitions on applied strains for which localization should occur in pure Fe and a high-strength steel. Results show, among other trends for the two materials, that shear localization in conjunction with phase transformation is promoted when the transformed phase is softer than the parent phase. Localization that would occur in the isolated parent phase can be mitigated if strain hardening or thermal softening tendencies of the transformed phase are sufficiently increased or reduced, respectively.

First-principles study of Ti adsorption on Al4C3 (0001) surface

Al4C3 phase is hypothesized to undergo a solid–solid phase transition into TiC, thereby facilitating the heterogeneous nucleation of α-Al. However, capturing this transition process experimentally is challenging, which undermines the credibility of this transition theory. In this study, first-principles calculations are employed to investigate the feasibility of Ti atom adsorption on the exposed (0001) surface of the Al4C3 crystal, providing theoretical support for the phase transition hypothesis. The findings indicate that Ti adatoms can effectively adsorb on the C-terminated (0001) surface, whereas adsorption on the Al-terminated surface is thermodynamically unfavorable. Upon structural optimization, Ti adatoms at bridge site B, top site T, and hollow site H1, irrespective of coverage, migrate towards the most stable hollow H2 site. Electronic structure analysis reveals that the bonding between the Ti adatom at the H2 site and the surface layer C atoms is primarily covalent, while the bonding with subsurface layer Al atoms is metallic. Additionally, Ti atom adsorption induces polarization of the bonding electron cloud between Al and C atoms. This study provides theoretical support for the Ti-induced transformation of the Al4C3 to TiC phase via surface adsorption, paving the way for the development of high-performance master alloys based on phase transition theory.

Tremendous Stiffness‐Changing Polymer Networks Enabled by Touch‐Induced Crystallization

AbstractStiffness‐changing polymers are critically needed for intelligent and adaptive applications in soft robotics and wearable electronics; however, they suffer from the requirement of persistent external stimulation. Herein, a stiffness‐changing polymer network impregnated with a supercooled ionic liquid is introduced, which undergoes touch‐induced crystallization from a soft ionogel to a stiff plastic. The network exhibits a remarkable tunability in stiffness change, with the highest value exceeding 190 000 times between the soft and stiff states (3.5 kPa vs 691.1 MPa). This tremendous transition is achieved through the first‐order liquid–solid phase transition of the supercooled ionic liquid, which is highly reversible and isochoric via a heating‐cooling process. Unlike traditional stimuli, only a single touch is needed without sustained stimulation to trigger the stiffening from soft to stiff states. Importantly, the touch‐responsive polymer network can be extended to various types of ionic liquids and monomers, indicating excellent strategic versatility. Moreover, this unique ionogel exhibits switchable adhesiveness and ionic conductivity, effectively demonstrating smart adhesives and ionic switches with enhancements of more than 66 and 5800 times, respectively. This work provides a facile and versatile strategy for designing stable stiffness‐changing polymers, unlocking significant potential applications for next‐generation smart devices.

Generalized mechanism for the solid phase transition of M2O3 (M=AI, Ga) featuring single cation migration and martensitic lattice transformation

Generalized mechanism for the solid phase transition of M2O3 (M=AI, Ga) featuring single cation migration and martensitic lattice transformation

Investigation of nanoscale dual-precipitation behavior in 4Cr16MoCu martensitic stainless steel under varied tempering temperatures

Nanoscale dual-precipitation in 4Cr16MoCu martensite stainless steel was investigated after tempering at 400 °C, 500 °C and 600 °C. Atom probe tomography (APT) was utilized to quantify the growth pattern of Cu-rich phase and eutectoid behavior of the co-located Cu-rich phase and M23C6 carbide precipitates. With the increase in tempering temperature, the size of Cu-rich phase continued to grow while their number decreased. Meanwhile, significant changes of the aggregation positions of Ni and Mn in Cu-rich particles were observed, shifting from the center of Cu particles when tempering at 500 °C to their periphery at 600 °C. During the precipitation process, closely adjacent Cu-rich particles were confirmed surrounding the carbides, indicating that carbides contribute to the nucleation of Cu-rich phase. Furthermore, despite their proximity, no mutual compositional encroachment between the precipitates was detected. In addition, the dislocation proliferation induced by the solid phase transition of Cu particles has also been confirmed.

Phase Transition Control in Molecular Solids via Complementarity of Hydrogen-Bond Strength.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin CoII compounds were isolated and systematically investigated by modifying the ligand terminal groups (X=S, Se) and substituents (Y=Cl, Br). S-Cl and Se-Br undergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX- ligands, accompanied by switchable magnetism. Conversely, S-Br and Se-Cl retain stability in ordered and disordered phases, respectively. H-bonds geometric analysis and ab initio calculations reveal that the electronegativity of X and Y affects the strength of NY-ap-H⋅⋅⋅X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor and vice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective.

A novel design of lithium-polymer pouch battery pack with passive thermal management for electric vehicles

This study investigates the thermal characteristics of a lithium polymer pouch battery thermal management system using phase change material (PCM) during the discharge. The research provides a detailed discussion of various factors influencing the system. The novelty aspect of this study involves evaluating thermal changes in the battery at 40 °C through hot soaking experiments comparing with both PCM-integrated modules and without PCM modules. The study further aims to identify the optimal PCM for both normal and high ambient conditions. Thermal parameters, including maximum temperature Tmax, average temperature Taverage and thermal gradient ΔT were evaluated at 25 °C and hot soaking performance at 40 °C temperature during discharge was analysed. Simulation were conducted to compare module behavior, especially at high-temperature conditions. Furthermore, a thorough examination of PCM melting and solid-phase transitions at high temperatures were performed that significantly impact the cooling performance of the PCM system. Our findings reveal that expanded graphite PCMs offers effective thermal performance with observed improvement of 27 %. Therefore, we recommend employing EG26 and EG28 PCMs for real-world application electric vehicle battery pack systems.

Heat capacities and role of defects in ion transfer of quinuclidinium hexafluorophosphate plastic crystal

To study the phase behavior and role of defects in the ion conduction of a well-investigated plastic crystal electrolyte, we measured the low-temperature heat capacities of quinuclidinium hexafluorophosphate ([HQ]PF6) plastic crystal and the defects of pure [HQ]PF6 and its mixtures containing lithium ions and chloride ions. The heat capacities of the pure material show two solid‒solid phase transitions at room temperature and a low temperature. Positron annihilation lifetime spectroscopy (PALS) revealed the phase dependence of the defect size for both the pure material and the mixtures. The defects in these two mixtures expand largely to approximately 2 (with Li+) and 2.5 (with Cl−) times larger than those in the pure material. The relationships between the ionic conductivity and vacancy volume of the pure material and the mixtures obey the Cohen−Turnbull free volume model, which is also phase dependent. This work help elucidate defect-assisted ion transfer in organic ionic plastic crystals.

Prediction of First-Order Phase Transition with Electron-Phonon Interaction.

Phase transitions in solids occur due to the shifting balance between the binding energies and entropic contributions of different crystal structures, even though the underlying Hamiltonian remains the same. This work demonstrates that incorporating electron-phonon interactions in the Hamiltonian results in distinct free energies at different temperatures, thus leading to a first-order phase transition. Contrary to prior investigations, taking into consideration the quantum mechanical kinetic energy operator of the nucleus by employing Bogoliubov's inequality yields a first-order phase transition. An equation is implicitly derived to determine the critical temperature of the first-order phase transition. Furthermore, an estimation is made to evaluate the latent heat and the resulting positional displacement of the nucleus. Comparing the present findings with previous ones allows setting parameter boundaries for both first- and second-order phase transitions.

Beyond Born-Oppenheimer Treatment for Multi-State Photoelectron Spectra, Phase Transitions of Solids and Scattering Processes

The “completeness” and “accuracy” of first principle based Beyond Born-Oppenheimer (BBO) theory is reviewed with its theoretical developments and wide applications on various realistic spectroscopic systems, scattering processes and pervoskite molecules exhibiting phase transition phenomena. Over the last two decades, our group has formulated as well as implemented the BBO treatment to construct diabatic Hamiltonian for several spectroscopically interesting molecules (NO2 radical, Na3 and K3 clusters, NO3, C6H6+,1,3,5-C6H3F3+ and C4N2H4), octahedral units of perovskites ( MnO69− and TiO68− ) involving solid state phenomenon as well as triatomic reactive scattering processes ( H3+ , HeH2+ and F+H2) to depict the effects of electron-nuclear couplings. Such diabatic Hamiltonians have been further used to perform quantum dynamical calculations to obtain observables (photoelectron spectra for spectroscopic/solid state systems and cross-sections/rate constants for scattering processes), which show excellent agreement with the recent experimental findings. In summary, this article provides the current perspective of BBO approach as well as Jahn-Teller (JT) theory with various applications on molecular systems/chemical processes.

An aberrant fused in sarcoma liquid droplet of amyotrophic lateral sclerosis pathological variant, R495X, accelerates liquid–solid phase transition

Intracellular aggregation of fused in sarcoma (FUS) is associated with the pathogenesis of familial amyotrophic lateral sclerosis (ALS). Under stress, FUS forms liquid droplets via liquid–liquid phase separation (LLPS). Two types of wild-type FUS LLPS exist in equilibrium: low-pressure LLPS (LP-LLPS) and high-pressure LLPS (HP-LLPS); the former dominates below 2 kbar and the latter over 2 kbar. Although several disease-type FUS variants have been identified, the molecular mechanism underlying accelerated cytoplasmic granule formation in ALS patients remains poorly understood. Herein, we report the reversible formation of the two LLPS states and the irreversible liquid–solid transition, namely droplet aging, of the ALS patient-type FUS variant R495X using fluorescence microscopy and ultraviolet–visible absorption spectroscopy combined with perturbations in pressure and temperature. Liquid-to-solid phase transition was accelerated in the HP-LLPS of R495X than in the wild-type variant; arginine slowed the aging of droplets at atmospheric conditions by inhibiting the formation of HP-LLPS more selectively compared to that of LP-LLPS. Our findings provide new insight into the mechanism by which R495X readily forms cytoplasmic aggregates. Targeting the aberrantly formed liquid droplets (the HP-LLPS state) of proteins with minimal impact on physiological functions could be a novel therapeutic strategy for LLPS-mediated protein diseases.

Strengthening of duplex Mg–9Li–3Al–2Zn–1Sn alloy by solid solution and mixed rolling-induced second phase transition

This work investigated the microstructure and mechanical properties of Mg–9Li–3Al–2Zn–1Sn alloy after solid solution and mixed rolling (hot rolling followed by room-temperature rolling). The research results reveal that after solid solution, AlLi and Mg2LiZn3 phases disappear, while MgLi2Al phases partially disappear. The hardness of the β-Li phase is much higher than that α-Mg phase, and the strength of the alloy is significantly increased while the elongation decreases to 1.4 %. Low plasticity is mainly due to lattice distortion and the presence of coarse Sn-rich phases. After mixed rolling, a large quantity of second phase precipitation in the alloy plays a role of second phase strengthening. The Mg17Al12 phases are observed to precipitate inside the α-Mg phase, and the AlLi phases containing MgLi2Al and Mg2LiZn3 nanophases inside are found at the β-Li phase and α-Mg/β-Li phase interface. The YS and UTS of the mixed rolled alloy reach 253 MPa and 273 MPa, respectively, with an improved EL of 18.4 %.

Understanding variations of thermal hysteresis in barocaloric plastic crystal neopentyl glycol using correlative microscopy and calorimetry

Plastic crystals (PCs) exhibit solid–solid order-disorder first-order phase transitions that are accompanied by large correlated thermal and volume changes. These characteristics make PCs promising barocaloric solid-state working bodies for heating and cooling applications. However, understanding the variation of transition temperatures and thermal hysteresis in PCs with cycling is critical if these materials are to replace traditional gaseous refrigerants. Here, for the archetypal barocaloric PC neopentyl glycol (NPG), we correlate microstructure obtained from scanning electron microscopy with local and total thermal changes at the phase transition from infra-red imaging and calorimetry, respectively. We outline an evolution in microstructure as NPG recrystallises during repeated thermal cycling through its solid–solid phase transition. The observed microstructural changes are correlated with spatially inhomogeneous heat transfer, yielding direct insight into the kinetics of the phase transition. Our results suggest that the interplay of these processes affects the undesirable thermal hysteresis and the nature of the kinetic steady-state microstructures that are stabilised during cycling between the ordered and disordered phases. These observations have implications for using NPG and other PCs as technologically relevant barocaloric materials and suggest ways in which the hysteresis in these types of materials may be modified.