Thermal Expansion Coefficient Research Articles

Thermal Transport and Thermal Polarization of Water in the Supercooled Regime.

The behavior of water in the deep supercooled regime has attracted significant interest, motivated by the hypothesis of the second critical point of water. Previous studies indicated the existence of a water anomaly, characterized by a minimum in the thermal conductivity of water. Here, we employ nonequilibrium molecular dynamics computer simulation and the TIP4P/2005 water force field to investigate the thermal conductivity of supercooled water targeting four different isobars, 1, 200, 700, and 1200 bar. We demonstrate using NEMD simulations the existence of minima in thermal conductivity associated with the maximum isothermal compressibility and the minimum speed of sound in water, hence establishing a firm connection with the second critical point of liquid water. Moreover, we demonstrate that thermal gradients polarize supercooled water with a thermal polarization coefficient of several mV/K. We explain the thermal polarization effect using a theoretical formulation introduced recently that connects the thermal polarization effect to the isobaric thermal expansion coefficient.

Unraveling Superior Elasticity and Controlled Thermal Expansion in Trigonal MBO3 (M=Al, Ga) with Isolated [BO3] Group: A Theoretical Perspective

AbstractA comprehensive theoretical investigation employing density functional theory explores the electronic structure, temperature‐dependent elasticity, thermodynamic properties, and chemical bonding of trigonal MBO3 (M=Al, Ga) with isolated [BO3] groups. The results uncover MBO3 (M=Al, Ga) as indirect semiconductors with superior mechanical stability, characterized by greater resistance to volume compression over shear deformation. Their elasticity exhibits relatively weak temperature dependence, suggesting excellent thermal stability. Thermodynamic analysis predicts that GaBO3 has a higher thermal expansion coefficient than AlBO3, approximately 2.1×10−5 K−1 and 1.8×10−5 K−1 at 300 K, respectively. Significantly, the overall thermal expansion coefficients of GaBO3 and AlBO3 are lower compared to other borate materials containing isolated [BO3] groups. Chemical bonding insights reveal that GaBO3′s larger thermal expansion is attributed to its larger atomic displacement parameters and weaker Ga−O bond strength. This research positions MBO3 (M=Al, Ga) as prime candidates for optical device applications due to their well‐characterized elasticity and controlled thermal expansion.

Strain tunable electronic, optical, and photovoltaic properties of monolayer β2-SrX2Y4 (X = Al, Ga, In, Y = S, Se)

In recent years, the experimentally synthesized two-dimensional material MoSi2N4, known for its excellent mechanical strength and environmental stability, has attracted significant attention as a representative of the MA2Z4 family. However, people's understanding of some MA2Z4 materials is still limited. In this study, we systematically investigated the properties of monolayer β2-SrX2Y4 (X=Al, Ga, In; Y=S, Se) with a seven-layer atomic configuration using first-principles calculations, focusing on their response to external strain engineering. Our results demonstrate that monolayer β2-SrX2Y4 exhibits characteristics of a direct bandgap semiconductor, and the majority of these materials retain these characteristics under applied strain. However, an unexpected transition from a direct bandgap to an indirect bandgap was observed in monolayer β2-SrAl2S4 under strain. Moreover, as strain changes from compressive to tensile, the imaginary part peak of the dielectric function for most β2-SrX2Y4 materials shifted towards lower energies (redshifted). Notably, in their pristine structures, only β2-SrAl2S4 and β2-SrAl2Se4 can facilitate water splitting by crossing the oxidation and reduction potentials of water. By applying strain, we successfully enabled β2-SrGa2S4 and β2-SrIn2S4 to possess the capability to drive water oxidation–reduction reactions. Furthermore, we calculated the second-order elastic constants and analyzed the Grüneisen parameter and thermal expansion coefficient based on the fitted energy density and strain relationships. This study highlights the potential applications of β2-SrX2Y4 in photocatalysis and optoelectronic devices and provides valuable insights for implementing biaxial strain in two-dimensional materials.

Homogenization of Thermal Properties in Metaplates.

Three-dimensional metamaterials endowed with two-dimensional in-plane periodicity exhibit peculiar thermoelastic behaviour when heated or cooled. By proper design of the unit cell, the equivalent thermal expansion coefficient can be programmed and can also reach negative values. The heterogeneity in the third direction of such metamaterials also causes, in general, a thermal-induced deflection. The prediction of the equivalent thermal properties is important to design the metamaterial suitable for a specific application. Under the hypothesis of small thickness with respect to the global in-plane dimensions, we make use of asymptotic homogenization to describe the thermoelastic behaviour of these metamaterials as that of an equivalent homogenous plate. The method provides explicit expressions for the effective thermal properties, which allow for a cost-effective prediction of the thermoelastic response of these metaplates.

Field-assisted sintering of MC-Ti3SiC2 composites with adjustable thermal expansion coefficient

Tool materials for precision glass moulding made of WC or SiC bear the risk of glass breakage due to a difference in the coefficient of thermal expansion (CTE) between the mould and the glass. The aim of this study is to develop a MAX phase composite with increased CTE and thus reduced CTE difference. A mixture of Ti3SiC2 and 10 vol% SiC powder was sintered between 1250 °C and 1350 °C using the field-assisted sintering technique (FAST). In addition to the sintering temperature, the dwell time and the initial particle size were varied using a full factorial experimental design. Complete densification, homogeneous carbide distribution and no grain coarsening were observed for specimens sintered at 1300 °C for 10 min at 50 MPa. The grain size of SiC and Ti3SiC2 is approximately 0.3 μm, although larger grains occasionally occur. Identified process parameters were successfully transferred to TiC reinforced Ti3SiC2 composites. While the carbide content can be specifically controlled by mixing, the MAX phase partially decomposes during sintering. MC additions between 10 and 30 vol% resulted in an adjustable CTE in the range 6.8–9.0 ppm/K.

Study of freeze-thaw deterioration of saturated and unsaturated hydraulic concrete based on measured strain

In actual concrete water projects, areas such as the back surface, above-water surface, and even areas where the water level fluctuates are in the unsaturated freeze-thaw state. The complexity of freeze-thaw tests of unsaturated hydraulic concrete has thus far prevented a sound understanding of the mechanisms at work in freeze-thaw deterioration of unsaturated hydraulic concrete. Given this situation, this study first compares three different unsaturated hydraulic concrete freeze-thaw test processes (polyurea seal, paraffin seal, and vacuum-bag seal) and then uses the vacuum-bag seal method to implement freeze-thaw tests of unsaturated hydraulic concrete. Afterward, three test schemes (unsaturated sealed freeze-thaw, water-freeze-thaw without air-entraining agent, and water-freeze-thaw with air-entraining agents) are conducted and the mechanisms of freeze-thaw deterioration of saturated and unsaturated hydraulic concrete are evaluated based on the measured temperature and strain of the concrete specimens. The results reveal a continuous and irreversible deterioration leading to the freeze-thaw damage of unsaturated sealed freeze-thaw specimens and water-freeze-thaw specimens with and without an air-entraining agent. After 200 freeze-thaw cycles, the cumulative residual strain of the aforementioned three test schemes reach 47 με, 616 με, and 273 με, respectively. The thermal expansion coefficient of concrete remains relatively constant with increasing freeze-thaw cycles. Water-freeze-thaw specimens without air-entraining agents have a greater thermal expansion coefficient than those with air-entraining agents, and unsaturated sealed freeze-thaw specimens have the smallest thermal expansion coefficient. The frost heave coefficient increases with increasing freeze-thaw cycles, and water-freeze-thaw specimens without air-entraining agents have greater frost heave coefficients than those with air-entraining agents.

Tri-functionally modified spherical silica for high-performance epoxy resin sealant

The integration of inorganic nanoparticles as reinforcement imparts epoxy resin with outstanding comprehensive performance, facilitating the utilization across diverse applications spanning coatings, adhesives, and composites. However, the persistent challenge lies in achieving optimal interfacial compatibility between the fillers and the resin matrix. This study focuses on the synthesis of tri-functionally modified spherical silica particles with an average size of 700 nm by empolying three distinct types of silane coupling agents in a synergistic manner to achieve desired functionalization. These agents endow the resulting particles with reactive groups, including epoxy and amine functionalities, which enhance interfacial compatibility and adhesion between the silica particle fillers and the epoxy resin matrix. Additionally, the incorporation of non-reactive phenyl groups serves to reduce the viscosity of resin composites. These modified silica particles are integrated into the sealant formulations, which exhibits commendable reliability and processability. It exhibits a 95 % reduction in moisture permeability, an increase in glass transition temperature by approximately 30 °C, and a decrease in coefficient of thermal expansion by 5∗10−6/k, compared to the sealant prepared with unmodified silica. The outcomes of this research present promising avenues for the advancement of cutting-edge display technologies.

Delamination analysis of the epoxy impregnated REBCO racetrack coil under thermal stress based on a 3D model

Superconducting coils made of Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) exhibit superior electromagnetic performance. Employing epoxy impregnation can improve the structural integrity of the superconducting coils. However, the delamination behavior is observed in the epoxy impregnated REBCO coil when the environment temperature cool from the room temperature to 77 K. In previous studies, there is a few researches on the delamination and mechanical behavior of the epoxy impregnated racetrack coil. Therefore, this study proposes a three-dimensional (3D) mechanical-thermal model which incorporates the cohesive zone material (CZM) to investigate the delamination mechanisms in epoxy impregnated REBCO racetrack coils during cooling. We found that the coil experienced a higher tensile radial stress at the semicircular part than the straight part during the cooling process. This leads to that the delamination area tends to appear initially in the semicircular part with large tensile radial stress. And the stress concentration generated at the edge of the delamination area in the semicircular part can cause the extension of the edge of the delamination area to the straight part. In addition, the influences of the thermal expansion coefficient (CTE) of the mandrel and overband on the coil delamination behavior are studied in this paper. It is found that the radial stress, the initial position of the delamination, and the degree of delamination are affected by the CTE of the mandrel and overband. And the delamination of the coil can be avoided by reducing the tensile radial stress of the coil through reducing the CTE of the mandrel or increasing the CTE of the overband. And the prevention of the delamination in the semicircular part can obviously avoid the occurrence of the delamination in the straight part of the racetrack coil.

Numerical investigation of the thermal hydrofracturing behavior of the Callovo-Oxfordian claystone

This study addresses the thermal hydrofracturing behavior in claystone within the context of the high-level and intermediate-level long-lived radioactive waste disposal. The heat generated by the waste packages will lead to a temperature increment within the host formation, inducing a pore pressure build-up essentially due to the difference between the thermal expansion coefficient of the pore water and that of the solid skeleton. If the induced pore pressure build-up is too high, the host formation will experience tensile stresses, potentially exceeding its tensile strength and resulting in fracturing. Understanding of these processes and improving numerical models to reproduce them will help the design, optimization, and safety of the repository. Additionally, it will contribute to demonstrating robustness by showing that such processes are not expected to occur at the repository scale.This study was conducted as part of the DECOVALEX-2023 project and synthesizes the efforts of six research teams modelling laboratory thermal extension tests conducted on Callovo-Oxfordian claystone (COx) samples, as well as an in-situ thermal hydrofracturing experiment conducted at the Meuse/Haute-Marne Underground Research Laboratory in France. The teams used different numerical codes with different approaches, including continuum and discrete approaches, to model these two tests. The laboratory tests were used to calibrate the teams’ models, such as the fracturing criterion. The teams considered a thermo-hydromechanical formulation under saturated conditions. One of the key features of their models was the incorporation of changes in the hydraulic properties of the COx through hydromechanical coupling.The approaches developed by the teams demonstrated their capability to analyze and reproduce fracture initiation in the COx in terms of time of occurrence and location based on their respective stress analyses. However, attempts to reproduce fracture aperture or fracture propagation were less accurate and remain areas for future research, which were beyond the scope of this study.

Study on Thermal Cycling Reliability of Epoxy-Enhanced SAC305 Solder Joint.

In this work, epoxy was added into commercial Sn-3.0Ag-0.5Cu (SAC305) solder paste to enhance the thermal cycling reliability of the joint. The microstructure and fracture surface were observed using a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and a shear test was performed on the thermally cycled joint samples. The results indicated that during the thermal cycling test, the epoxy protective layer on the surface of the epoxy-enhanced SAC305 solder joint could significantly alleviate the thermal stress caused by coefficients of thermal expansion (CTE) mismatch, resulting in fewer structural defects. The interfacial compound of the original SAC305 solder joints gradually coarsened due to the accelerated atomic diffusion, but epoxy-enhanced SAC305 solder joints demonstrated a thinner interfacial layer and a smaller IMC grain size. Due to the reduced stress concentration and the additional mechanical support provided by the cured epoxy layer, epoxy-enhanced SAC305 solder joints displayed superior shear performance compared to the original joint during the thermal cycling test. After 1000 thermal cycles, Cu-Sn IMC regions were observed on the fracture surfaces of the original SAC305 solder joint, exhibiting brittle fracture characteristics. However, the fracture of the SAC305 solder joint with 8 wt.% epoxy remained within the solder bulk and exhibited a ductile fracture mode. This work indicates that epoxy-enhanced SAC305 solder pastes display high thermal cycling reliability and could meet the design needs of advanced packaging technology for high-performance electronic packaging materials.

Zero thermal expansion in KxMnxIn2-x(MoO4)3 based materials

Zero thermal expansion (ZTE) materials can solve problems such as device failure and cracking caused by mismatched coefficient of thermal expansion. However, ZTE material is rare in nature. NaZr2(PO4)3 is a framework compound with near-zero thermal expansion due to coupled rotations of rigid ZrO6 and PO4 polyhedra in the structure, and several studies have been devoted to obtaining more ZTE compounds by chemical substitution of Na or Zr. Inspired by the AAV concept we proposed, in this work, the PO4 tetrahedra with a small volume has been replaced by the large volume MoO4 tetrahedra in KxMnxIn2-x(MoO4)3 (x = 0.4, 0.6, 0.8, and 1.0) compounds to provide more space for the coupling rotation of the polyhedron, and reduce the coefficient of thermal expansion. On the other hand, the flexibility of the framework structure has been modulated by the content of K+ to achieve new ZTE materials, and the effects of K+ content on crystal structure and thermal expansion have been analyzed in detail by combining variable temperature XRD and Raman. These findings not only provide more ZTE materials, but also suggest a promising design method for ZTE materials.

Exploring bonding temperature variations in diffusion brazing of B4C ceramics with Ni-Cr-Si-Fe-B interlayer: Mechanical and microstructural analysis

This study examines the impact of the bonding temperature parameter on the quality of diffusion brazing joints of B4C ceramics using a Ni-Cr-Si-Fe-B interlayer. Various factors including shear strength, hardness, microstructure, interfacial phenomena, elemental diffusion patterns, formed compounds and phases, and fracture surfaces of the samples were analyzed and compared. The brazed sample at 1110 °C for 1/2 h exhibited the highest shear strength of 62 MPa. Increase of the bonding temperature to the optimum level (1090–1110 °C) enhances the fluidity of the molten interlayer, facilitating its diffusion into the porosities of the ceramic components. This increase also promotes higher interactions within the system, creating favorable conditions for element diffusion. However, surpassing the optimum temperature (1110–1130 °C) may lead to increased destructive reactions and intensify the impact of the coefficient of thermal expansion (CTE) mismatch, resulting in residual stresses and a subsequent decrease in bond strength. The excessive increase in the bonding temperature (1130–1150 °C) can lead to the excessive fluidity of the molten interlayer, potentially causing effusion onto the joint's fixture and damaging the samples. The results indicate the formation of various compounds between the elements of the interlayer and carbon and boron elements, including SiC, Ni4B3, CrB2, Fe2B, Ni6Si2B, and B2Fe3Ni3, at the fracture surface of the sample bonded at 1110 °C. The more substantial peaks of these compounds, compared to other samples, could be a reason for the higher strength of this particular sample.

Effects of Pr substitution in Y1-xPrxBaCo3ZnO7+δ (0 ≤ x ≤ 0.5) cathodes for intermediate temperature solid oxide fuel cells

In this investigation, we successfully synthesized a series of Swedenborgite-type Y1-xPrxBaCo3ZnO7+δ (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5, abbreviated as YPxBCZ) oxides by a solid-state reaction method. The results show that YPxBCZ (x = 0.0, 0.1, 0.2, and 0.3) are single-phase structures, but YP0.4BCZ and YP0.5BCZ show interesting self-assembled composite phases. After long-term phase stability testing, YP0.3BCZ showed the best thermal stability. All samples show good chemical and thermal compatibility with La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte. The thermal expansion coefficients in the temperature range from 30 °C to 1000 °C are equal to 9.8-13.1 × 10−6 K−1, close to that of the LSGM electrolyte. It is also found that Pr doping improves high temperature conductivity of YPxBCZ. The conductivity of YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ reach 15.1, 18.5, and 22.5 S cm−1 at 800 °C. In addition, the area specific resistance (ASR) value decreases as the Pr content increases (0.038, 0.033, and 0.027 Ω cm2 at 800 °C for YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ), improving the catalytic activity of the material. Another interesting finding was that the ASR of samples subjected to high temperature thermal decomposition was not adversely affected by the presence of decomposition products. The maximum power densities of YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ in the single cells at 800 °C were 845, 930, and 1044 mW cm2, respectively. These results indicate that YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ are promising cathode materials for intermediate-temperature solid oxide fuel cell.

Structure, J-O analysis, and near-infrared luminescence of Er3+/Yb3+ doped SiO2–B2O3-GdF3-CaO-Bi2O3 glass

SiO2–B2O3-GdF3-CaO-Bi2O3 doped glasses containing Er3+/Yb3+ ions at varying concentrations were successfully synthesized using a high-temperature melting method. The glass samples' physicochemical properties and amorphous structure were characterized through density, XRD, XPS, FT-IR, and Raman analyses. Thermal expansion coefficient testing indicated good thermal stability of the glass system. Increasing the Yb3+ doping concentration enhanced near-infrared luminescence at 1.53 μm, with maximum luminescence intensity at approximately 3.2 mol% doping concentration. The energy transfer mechanism of Er3+/Yb3+ doped SiO2–B2O3-GdF3-CaO-Bi2O3 glass was elucidated through fluorescence spectrum analysis, revealing J-O parameters Ω2 = 11.2 × 10−20 cm2, Ω4 = 8.9 × 10−20 cm2, and Ω6 = 9.59 × 10−20 cm2. Calculations for absorption cross-section, cross-section of emission, and gain curve additionally reinforced the glass's capability for laser uses.

Effect of Yb3+ on the thermophysical and mechanical properties of gadolinium zirconate ceramics: First-principles calculations and experimental study

Thermal barrier coating materials require high phase stability, low thermal conductivity, and a thermal expansion coefficient that matches the bonding layer. Cation doping is a highly efficient method for enhancing the thermophysical and mechanical characteristics of materials used in thermal barrier coatings. The thermophysical and mechanical properties, as well as the phase stability at high temperatures of ceramic materials doped with Yb3+ in gadolinium zirconate, are examined by utilizing first principles calculations and solid-state reaction methods. As the Yb3+ content increases, the grain average particle size of gadolinium zirconate ceramics first decreases and then increases. Given that a smaller grain size results in more grain boundaries, thereby reducing the thermal conductivity of the material, it can be inferred that Yb0.20 ((Gd0.8Yb0.2)2Zr2O7) with the smallest grain size exhibits lower thermal conductivity. As the Yb3+ content increases, both the calculated and experiment results suggest the Young’s modulus of gadolinium zirconate initially declines to its minimum value when the Yb3+ content is 0.5 and subsequently experiences a little increase. Furthermore, as the concentration of Yb3+ increases, the material initially experiences a drop in both hardness and fracture toughness, followed by a subsequent increase. Both the calculation and experimental results indicate that the thermal conductivity of gadolinium zirconate initially decreases and then increases. Among the different compositions, Gd1.5Yb0.5Zr2O7 demonstrates the minimum thermal conductivity, measuring 1.029 W/(m⸱K) according to the Clark model and 1.152 W/(m⸱K) according to the Cahill model. At a temperature of 1273 K, the experimental results demonstrated that (Gd0.8Yb0.2)2Zr2O7 has the lowest thermal conductivity of 1.415 W/(m·K). Furthermore, both the calculated and experimental thermal expansion coefficients of the material decrease first until the Yb3+ concentration is 0.5 and then increase slightly when the Yb3+ content increases. Moreover, gadolinium zirconate ceramics have demonstrated a consistent single-phase fluorite structure, excellent stability at high temperatures, and remarkable structural integrity during repeated heating and cooling cycles. The calculation results exhibit strong congruence with the experimental data. The objective of this work is to improve the thermophysical and mechanical properties of gadolinium zirconate ceramics for their application as materials for thermal barrier coatings.

Effects of CeO2 doping on the mechanical, infrared radiative, and thermophysical properties of Pr2Zr2O7 ceramics for potential thermal protective coatings

A series of Ce4+-doped Pr2Zr2O7 ceramics were produced using a solid reaction method to utilize novel ceramic materials as potential candidates for thermally protective coatings. The effects of Ce4+ doping on the phase composition and mechanical, infrared radiative, and thermophysical properties were studied in detail. The results indicated the good phase stability and sintering resistance of the Pr2(Zr1−xCex)2O7 ceramics. Moreover, Ce4+-doped Pr2Zr2O7 bulk materials exhibited higher infrared emissivity (0.904) at wavelengths of 3–5 μm and 1000 °C for Pr2(Zr0.5Ce0.5)2O7) owing to the introduction of impurity energy levels. Pr2(Zr0.7Ce0.3)2O7 exhibited an appropriate average coefficient of thermal expansion of 12.4 × 10−6 K−1 and a low thermal conductivity of 1.14 W m−1 K−1 at 1000 °C, owing to the reduction of lattice energy and the presence of more oxygen vacancies and substitution atoms.

Evolution process of T1 precipitate in Al–Cu–Li–TiC/TiB2 alloy during aging treatment

In this study, particle-reinforced aluminium matrix composites (PRAMCs) of an Al–Cu–Li alloy were prepared using nano-sized TiB₂+TiC particles. The relationship between TiB₂+TiC nanoparticles and T1 precipitates during the ageing process, as well as the influence of TiC + TiB₂ particles on the growth process of T1 precipitates during the ageing process, were investigated. The grain sizes of the A0 and A1 samples were found to be 249.89 μm and 86.42 μm, respectively. The dislocation density is greater in the deformed A1 sample. The coefficient of thermal expansion (CTE) effect generated by TiC and TiB₂ particles stimulates the precipitation process of T1 precipitates. The A1 alloy reached the peak ageing state in a shorter time and yielded a greater number of T1 precipitates. The precipitation process of T1 precipitate is: SSSS→T1P→T1. The transition from T1P (face-centered cubic, FCC) to T1 (hexagonal close packing, HCP) entails a modification in the order of packing. The recently formed T1P precipitate is attached to the established T1 precipitate and extends along the c-axis through the shared copper-rich layer that has formed on both sides of the mature T1 precipitate. The mechanical properties of sample A1 are optimal at T = 22h, with a yield strength, tensile strength, and elongation of 520 MPa, 553 MPa, and 8.2%, respectively. In comparison to the A0 sample, the yield strength and tensile strength exhibited an increase of 5.05% and 5.13%, respectively.

Simulation-Directed Construction of Bamboo-Forest-Like Heat Conduction Networks to Enhance Silicon Rubber Composites' Heat Conduction Properties.

Highly vertically thermally conductive silicon rubber (SiR) composites are widely used as thermal interface materials (TIMs) for chip cooling. Herein, inspired by water transport and transpiration of Moso bamboo-forests extensively existing in south China, and guided by filler self-assembly simulation, bamboo-forest-like heat conduction networks, with bamboo-stems-like vertically aligned polydopamine-coated carbon fibers (VA-PCFs), and bamboo-leaves-like horizontally layered Al2O3(HL-Al2O3), are rationally designed and constructed. VA-PCF/HL-Al2O3/SiR composites demonstrated enhanced heat conduction properties, and their through-plane thermal conductivity and thermal diffusivity reached 6.47W(mK)-1 and 3.98mm2s-1 at 12vol% PCF and 4vol% Al2O3 loadings, which are 32% and 38% higher than those of VA-PCF (12vol%) /SiR composites, respectively. The heat conduction enhancement mechanisms of VA-PCF/HL-Al2O3 networks on their SiR composites are revealed by multiscale simulation: HL-Al2O3 bridges the separate VA-PCF heat flow channels, and transfers more heat to the matrix, thereby increasing the vertical heat flux in composites. Along with high volume resistivity, low compression modulus, and coefficient of thermal expansion, VA-PCF/HL-Al2O3/SiR composites demonstrate great application potential as TIMs, which is proven using multiphysics simulation. This work not only makes a meaningful attempt at simulation-driven biomimetic material structure design but also provides inspiration for the preparation of TIMs.

Investigation on the hydrogen storage properties, electronic, elastic, and thermodynamic of Zintl Phase Hydrides XGaSiH (X = sr, ca, ba)

This study presents a comprehensive investigation of the electronic, mechanical, and thermodynamic properties of Zintl phase hydrides XGaSiH (X = Sr, Ca, Ba) using Density Functional Theory (DFT) and the FP-LAPW method within the WIEN2k package. Our analysis covers the structural stability, electronic properties, and hydrogen interaction mechanisms in these compounds. The hydrides exhibit narrow band gaps, with values ranging from 0.1 to 0.5 eV using GGA and LDA functionals, and 0.6–1.0 eV with mBJ-GGA and mBJ-LDA. The hydrogen storage capacities are determined to be 0.34 wt %, 0.47 wt %, and 0.40 wt % for SrGaSiH, CaGaSiH, and BaGaSiH, respectively, highlighting their potential for energy storage applications. Thermodynamic properties, evaluated through the quasi-harmonic Debye model, provide insights into the Grüneisen parameter, heat capacity, and thermal expansion coefficient over a range of pressures (0–50 GPa) and temperatures (up to 1000 K). Elastic constants reveal that these compounds are mechanically stable, with a notable anisotropy in the {100} plane and varying degrees of compressibility among the different hydrides. Our study further highlights the slightly ordered hexagonal Ga and Si layers, which contribute to the enhanced hydrogen storage capabilities of these materials. The compounds demonstrate high structural stability, facilitating effective hydrogen retention and release at practical temperatures, making them promising candidates for hydrogen storage applications. Additionally, the analysis of electronic band structures and density of states suggests significant conductivity potential, with band gaps ranging from 0.1 to 1.0 eV, depending on the computational method used. The unique combination of structural, electronic, thermodynamic, and mechanical properties in XGaSiH compounds positions them as valuable materials for renewable energy applications. These findings lay the groundwork for future research focused on optimizing these materials through structural modifications or doping to enhance performance metrics such as hydrogen storage capacity and electrical conductivity.

Structure and tribological behavior of a polyetherimide/polytetrafluoroethylene matrix filled with negative thermal expansion zirconium tungstate particles

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) α-ZrW2O8 (ii) at temperatures 23 °C, 120 °C and 180 °C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 °C and 180 °C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.