Linear Thermal Expansion Coefficient Research Articles

Negative Thermal Expansion Realized by an Incomplete Bimaterial Ring

Incomplete bimaterial ring (a circular ring with a gap) capable of producing negative macroscopic thermal expansion is proposed and its behavior is analyzed. The ring exhibits negative thermal expansion (NTE) (in the plane of the ring) when the outer ring has higher thermal expansion coefficient than the inner one. When the thermal expansion coefficients are equal (monomaterial incomplete ring), the effective (macroscopic) planar thermal expansion becomes zero. (The complete thermal expansion will be positive but small.) It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the role of the gap is played by the open ends. These structures will have higher stiffness than the incomplete bimaterial ring. The thermal expansion of the ring is characterized by the effective (macroscopic) coefficient of linear thermal expansion. The effective coefficient of linear thermal expansion depends on the temperature increase, making the thermal expansion nonlinear. Planar and 3D NTE structures are considered.

Spontaneous imbibition of unsaturated sandstone under different vertical temperature gradients: neutron radiography experiments and dynamic models

To elucidate the imbibition behavior of water in complex temperature and stress environments, spontaneous imbibition experiments were conducted on unsaturated matrix sandstones at different vertical temperature gradients by neutron radiography technology. Additionally, corresponding dynamic models of water imbibition in porous media were established. The research results reveal the phased characteristics of sandstone spontaneous imbibition and the influence of vertical temperature gradient on the evolution of wetting front. Specifically, the initial development speed of the wetting front increases with an increase in the vertical temperature gradient, indicating a direct relationship. However, the growth rate of the wetting front gradually slows down with increasing time, eventually reaching a saturated state. Model validation demonstrates that the traditional Washburn's law is still valid in isothermal conditions without temperature gradient (G=0). Further analysis indicates that the imbibition rate has a direct correlation with linear thermal expansion coefficient (α) and viscosity temperature coefficient (β) across various vertical temperature gradients, and an inverse correlation with surface tension temperature coefficient (γ). Furthermore, when the values of α, β, and γ fall below 0.001, their impact on the imbibition rate becomes negligible. The sensitivity of the imbibition rate to parameters γ, β, and α decreases in that order, with γ being the most sensitive, followed by β, and α being the least sensitive. Moreover, the relative importance of α, β, and γ dictates their specific influence on the imbibition rate, and a synergistic effect exists among these parameters, which collectively influence the water absorption behavior of sandstone.

Achieving ZT > 1 in Cu and Ga Co-doped Ag6Ge10P12 with Superior Mechanical Performance and Its Fundamental Physical Properties toward Practical Thermoelectric Device Applications.

Recently, phosphorus-based compounds have emerged as potential candidates for thermoelectric materials. One of the key challenges facing this field is to achieve ZT > 1, which is the benchmark for thermoelectric device applications. In this study, it is demonstrated that the thermoelectric performance of environmentally friendly Ag6Ge10P12 is enhanced by co-doping Cu and Ga. The mechanical properties, coefficient of linear thermal expansion, work function, and compatibility factor are comprehensively clarified to provide guidelines for reliable device applications. The peak and average dimensionless figures of merit of Ag5.85Cu0.15Ge9.875Ga0.125P12 reach 1.04 at 723 K and 0.63 at 300-723 K, respectively, which are the highest values for phosphorus-based thermoelectric materials. The Young's modulus, Vickers microhardness, fracture toughness, and compressive strength of Ag5.85Cu0.15Ge9.875Ga0.125P12 are 132 GPa, 589, 1.23 MPa m1/2, and 219 MPa, respectively, which are superior to those of typical state-of-the-art thermoelectric materials. The remarkable thermoelectric and mechanical performance of Ag5.85Cu0.15Ge9.875Ga0.125P12 mean that it is a promising candidate for medium-temperature thermoelectric conversion. Ti, V, Rh, and Pt are suitable for electrodes without exfoliation under thermal expansion and with ohmic contacts to Ag5.85Cu0.15Ge9.875Ga0.125P12 in terms of the coefficient of linear thermal expansion and work function. Considering that the compatibility factor of Ag5.85Cu0.15Ge9.875Ga0.125P12 is approximately 2.8, half-Heusler, skutterudite, and magnesium silicide-stannide compounds are suitable n-type thermoelectric counterpart materials in thermoelectric devices. These insights will lead to the development of phosphorus-based thermoelectric materials toward practical thermoelectric device applications.

Thermal Expansion of Hexagonal Boron Nitride

A heuristic model is proposed for the dependence with temperature of the linear coefficients of thermal expansion (TEC) of hexagonal boron nitride (hBN) parallel to the crystallographic a and c axes, namely and . The model proposed for the linear TECs of hBN is consistent with physical constraints at the low‐ and high‐temperature limits. The model's free parameters are determined by a multi‐objective fitting to literature data on lattice parameters and linear TECs versus temperature, as determined experimentally by X‐ray diffraction and interferometric techniques. For hBN, is negative up to 1290(170) K (more than twice the corresponding temperature for graphite), with a minimum of around 230 K. According to the calculations and literature data, the linear TEC should remain negative at least up to 9 GPa. Furthermore, the linear coefficient of thermal expansion should decrease with pressure as = .

The effect of changing constituents on tensile mechanical properties of HfNbTaTiZr high entropy alloy: A molecular dynamics study

The recent trend of high-entropy alloys (HEAs) was studied extensively for their promising mechanical properties, but individual constituents' effects have remained unexplored. In this work, the effects of changing the percentage of elements of HfNbTaTiZr-HEA on the mechanical properties were analyzed during uniaxial tension using molecular dynamics simulation. The tensile strength and modulus of elastic properties of the samples were analyzed. It was found that adding Nb or Ta up to 10 % (i.e. Nb10/Ta10) in the high entropy alloys increased the ultimate tensile strength (UTS) from 2.9 GPa in the base alloy to 3.8/3.9 GPa (Nb10/Ta10) respectively, but further increment of these elements to 30 % resulted in a downgrade of UTS to 2.7 GPa. Similarly, the modulus of elasticity increased from 117.7 (±3) GPa in the base alloy to 137.7/129 (±3) GPa (Nb10/Ta10) respectively, but fell to 112–115 GPa upon further increment. The initial increase in strength could be due to the solid solution strengthening mechanism. However, further increases in these elements might hinder the development of a homogeneous solid solution because of differences in atomic size and crystal structure, which could ultimately reduce the alloy's strength. However, the effect of Ti and Zr follows an opposite trend as compared to Nb and Ta. Furthermore, the optimum composition of HEAs alloys was analyzed using a surface-contour plot and suggests minimizing the inclusion of Ta for maximizing the UTS, E, and %Elongation. Also, the high-temperature behavior of the optimized HEA's alloy was analyzed which showed a deterioration in properties at elevated temperature. The fracture evolution of the samples showed cup and cone-type fractures propagating under strain, the linear thermal expansion coefficient of HfNbTaTiZr-HEA was also calculated and found closer to the literature value.

Size Effects in Climatic Aging of Epoxy Basalt Fiber Reinforcement Bar.

The purpose of this study was to obtain information on the influence of the size factor on the climatic aging of circular fiber plastics produced by pultrusion. The kinetics of moisture transfer was obtained in humidification and drying modes at 60 °C in samples of epoxy basalt fiber reinforcement bars: after 28 months of exposure in the extremely cold climate of Yakutsk and 30 months of exposure in the moderately warm climate of Gelendzhik. It was shown that the 2D Langmuir model adequately describes the kinetics. The diffusion coefficients in the reinforcement direction for bars with diameters of 6, 8, 10, 16 and 20 mm turned out to be significantly higher than in the radial direction. To clarify the aging mechanism of the bars and the tensile, compressive and bending strength, the coefficient of linear thermal expansion and the glass transition temperature of the epoxy matrix of the bars with a diameter of 6, 8 and 10 mm after 51 months of exposure in Yakutsk and 54 months of exposure in Gelendzhik were measured. It was shown that after climatic exposure, the deformability of the bars decreased with increasing diameter of the bar; the glass transition temperature increased more significantly in the bar with a smaller diameter. In 6 mm diameter bars, the compressive and bending strength limits decreased by 10-25 % due to the plasticizing effect of moisture. With the same depth of moisture penetration into the volume of the samples, its effect on the strength of thin bars was significant, and for thick bars, it was insignificant. An increase in the glass transition temperature by 6 °C, associated with the additional curing of the polymer matrix, occurred in the surface layer of the epoxy basalt fiber reinforcement bars and was revealed in bars with a smaller diameter.

A New Method for Temperature Dependent COM Parameters Extraction and Its Application to Simulation of SAW Devices

Abstract Surface Acoustic Wave (SAW) filters are widely used in mobile communication systems due to their superior performance. Yet, application scenarios for these SAW devices can be limited by temperature stability. The coupling of modes (COM) model is proved to be an efficient modeling approach to design SAW devices at present. However, temperature dependent COM parameter extraction is still absent. This work proposed a new method combining COM model with quasi-3D periodic finite element method (FEM) model coupled with thermal field, which can accurately and rapidly simulate and optimize the temperature stability of SAW devices. The COM parameters extraction method used in this study mainly depends on harmonic admittance. For a given temperature (T), the thermal effect can be computed by incorporating the linear thermal expansion coefficients and temperature coefficients of elasticity into the model. For validation, the admittance responses of a finite-length SAW resonator and the S-parameter of a double-mode SAW (DMS) for 42º YX-LiTaO3 piezoelectric substrate are calculated by using P-Matrix with the extracted COM parameters. For validation, the admittance responses of a SAW resonator on 42º YX-LiTaO3 under different temperature conditions is calculated. Furthermore, the temperature behaviors of a DMS filter on 42º YX-LiTaO3 are also analyzed based on the proposed method. Accurate predictions of the temperature behaviors for both resonator and filter were achieved and discussed. This investigation provides guidelines for design of high-performance SAW devices with good temperature stability.

Poly(ether ketone ketone)/hollow silica filler substrates and application for sixth generation communication

AbstractThe influence of density and shape of hollow silicas (silica hollow tubes (SHT) or hollow glass microspheres (HGM)) on dielectric and heat‐resisting characteristics of poly(ether ketone ketone) (PEKK)/SHT and PEKK/HGM films was systematically investigated. The dielectric characteristics of PEKK/SHT or PEKK/HGM films decrease to a minimum, as their SHT or HGM contents approach 8 or 20 wt%, respectively, and the minimum dielectric constant (εr) and dielectric loss (tan δ) of PEKK/SHT or PEKK/HGM films decrease visibly with decreasing SHT densities. By filling with 0.46 g cm−3 mean density of SHT or HGM fillers, the minimum εr and tan δ of PEKK/SHT films are somewhat smaller than those of PEKK/HGM films. The linear coefficient of thermal expansion (LCTE) values of PEKK/SHT or PEKK/HGM films reduce and their onset degradation temperature values increase gradually with increasing SHT and HGM contents. Low εr/tan δ (2.11/0.0022 and 2.2/0.0027 at 1 MHz), LCTE (35.5 × 10−6 and 31.2 × 10−6 °C−1) and excellent heat‐resisting properties favorable for sixth generation (6G) ultrarapid communication are realized for appropriately prepared PEKK/SHT and PEKK/HGM substrate films. The free‐volume‐hole characteristics of PEKK/HGM or PEKK/SHT films approach a maximum as SHT or HGM contents reach an optimum value of 8 or 20 wt%, respectively. © 2024 Society of Chemical Industry.

Machine learning enables the discovery of 2D Invar and anti-Invar monolayers

Materials demonstrating positive thermal expansion (PTE) or negative thermal expansion (NTE) are quite common, whereas those exhibiting zero thermal expansion (ZTE) are notably scarce. In this work, we identify the mechanical descriptors, namely in-plane tensile stiffness and out-of-plane bending stiffness, that can effectively classify PTE and NTE 2D crystals. By utilizing high throughput calculations and the state-of-the-art symbolic regression method, these descriptors aid in the discovery of ZTE or 2D Invar monolayers with the linear thermal expansion coefficient (LTEC) within ±2 × 10−6 K−1 in the middle range of temperatures. Additionally, the descriptors assist the discovery of large PTE and NTE 2D monolayers with the LTEC larger than ±15 × 10−6 K−1, which are so-called 2D anti-Invar monolayers. Advancing our understanding of materials with exceptionally low or high thermal expansion is of substantial scientific and technological interest, particularly in the development of next-generation electronics at the nanometer or even Ångstrom scale.

The diamond-silicon carbide composite Skeleton® as a promising material for substrates of intense X-ray beam optics.

The paper considers the possibility of using the diamond-silicon carbide composite Skeleton® with a technological coating of polycrystalline silicon as a substrate for X-ray mirrors used with powerful synchrotron radiation sources (third+ and fourth generation). Samples were studied after polishing to provide the following surface parameters: root-mean-square flatness ≃ 50 nm, micro-roughness on the frame 2 µm × 2 µm σ ≃ 0.15 nm. The heat capacity, thermal conductivity and coefficient of linear thermal expansion were investigated. For comparison, a monocrystalline silicon sample was studied under the same conditions using the same methods. The value of the coefficient of linear thermal expansion turned out to be higher than that of monocrystalline silicon and amounted to 4.3 × 10-6 K-1, and the values of thermal conductivity (5.0 W cm-1 K-1) and heat capacity (1.2 J K-1 g-1) also exceeded the values for Si. Thermally induced deformations of both Skeleton® and monocrystalline silicon samples under irradiation with a CO2 laser beam have also been experimentally studied. Taking into account the obtained thermophysical constants, the calculation of thermally induced deformation under irradiation with hard (20 keV) X-rays showed almost three times less deformation of the Skeleton® sample than of the monocrystalline silicon sample.

Novel kosnarite-based M0.5Zr2(AsO4)x(PO4)3-x (M – Sr, Ba and Cd) ceramics for radwaste incorporation

Mineral-like single-phase NZP materials of variable composition M0.5Zr2(AsO4)x(PO4)3−x (M − Sr, Ba, Cd) are of interest as matrices for isolation of high-level Sr, Ba and Cd wastes generated during reprocessing of irradiated nuclear fuel. Such polycrystalline phases were synthesized by sol-gel method with subsequent heat treatment and investigated by X-ray diffraction, IR spectroscopy and electron-probe microanalysis. Rietveld structure refinement showed that the framework is formed by ZrO6 octahedra and mixed AsO4/PO4 tetrahedra connected by vertices; Sr, Ba or Cd cations are located in extra-framework positions. Arsenate-phosphates can be classified as medium thermal expansion materials due to their average coefficient of linear thermal expansion of 2.8∙10−6 °C−1. Chemical durability test indicates that the leaching rate of Sr2+ ions from the NZP structure type solid solution is of the order of 10−5 g cm−2d−1.

The main strength material parameters of deformable cement adhesives

The deformable cement adhesives types C2S1 and C2S2 are usually used to glue ceramic slabs onto so-called critical substrates (other than concrete), including under changing weather conditions. The declared strengths of these adhesives attached to substrates can be found in the manufacturer’s standards and declarations. The use of cement adhesives on surfaces other than concrete or in other applications, such as a lightweight heated floor system (LHFS), should meet safety standards. To determine this, basic strength parameters for deformable adhesives, which have not been specified until now, need to be set. For this purpose, many analyses were performed, such as tensile and compressive strength tests, as well as the measurement of displacements in the thermal chamber, using, for example, digital image correlation and extensometric techniques. It was possible to define the main strength parameters of deformable adhesives, such as Young’s modulus (E), Poisson’s ratio (ν) and linear thermal expansion coefficient (α). These multiple measuring techniques were able to authenticate the obtained results, determining the maximum compressive strength of deformable adhesives, as well as longitudinal and transverse deformations. The research material parameters E, ν and α can be used for the calculation of LHFS with a heating coil, as well as for other building partitions or on critical substrates (different from concrete), using some of the many numerical methods available.

Carbon whiskers reinforced porous glassy carbon composites by synchronous growth

A crystalline and non-crystalline composite of pure carbon was proposed, which is a carbon whiskers reinforced porous glassy carbon composite, where crystalline carbon whiskers support the microscopic pores of non-crystalline glassy carbon matrix. Two allotropes of carbon were produced simultaneously and compounded together in a single high temperature treatment of thermosetting phenolic resin, with aluminum oxide (Al2O3) as a catalyst. A synchronous growth theory was proposed to explain the growth mechanism. In the pyrolysis process of phenolic resin to generate porous glassy carbon, hydrocarbon gas was produced and trapped in the generated pores. By the same time, the hydrocarbon gas in pores was decomposed and grew carbon whiskers by catalysis of Al2O3. With linear thermal expansion coefficient from 2.0∙10−6 to 3.8∙10−6 K−1, thermal conductivity from 1.763 to 2.518 W∙m−1 K−1, specific heat capacity from 0.396 to 0.752 J∙g−1 K−1, thermal diffusivity from 6.115 to 4.598 mm2 s−1, between room temperature (RT) and 500 °C, the Vickers hardness is at 65 MPa, and the fracture toughness is at 0.329 Mpa∙m1/2 in RT. The carbon whiskers reinforced porous glassy carbon composite keeps a balance between thermophysical and mechanical properties, showing its application value in thermal insulation materials and high temperature structure materials.

A Study on Measurement and Calculation Method for Coefficient of Linear Thermal Expansion of Low-Quality Aggregate

A Study on Measurement and Calculation Method for Coefficient of Linear Thermal Expansion of Low-Quality Aggregate

Poly(ester imide)s with Low Linear Coefficients of Thermal Expansion and Low Water Uptake (VIII): Structure-Flame Retardancy Relationship.

A series of ester-linked tetracarboxylic dianhydrides containing multiple para-phenylene units (TA-pPhs) was synthesized to obtain novel modified polyimides, namely poly(ester imide)s (PEsIs). The flame retardancy and film toughness of PEsIs tended to deteriorate with the structural extension of the repeating units (or monomers) via ester groups. To identify the structural factors necessary for achieving the highest flame retardancy rank (UL-94, V-0), we systematically investigated the structure-property relationships of a series of TA-pPh-based PEsIs. Among them, a PEsI derived from para-quaterphenylene-containing TA-pPh (TA-DPQP) and p-phenylenediamine (p-PDA) exhibited the best property combination, featuring an extremely high glass transition temperature (Tg), very low linear coefficient of thermal expansion (CTE), low water uptake (WA), ultralow linear coefficient of humidity (hygroscopic) expansion (CHE), unexpectedly high film toughness, and excellent flame retardancy (V-0 rank). Moreover, we examined the effects of substituents of TA-pPh and discussed the mode of action for the increased film toughness. This study also investigated the structure-property relationship for a series of PEsIs derived from isomeric naphthalene-containing tetracarboxylic dianhydrides. Some of the PEsIs obtained in this study, such as the TA-DPQP/p-PDA system, hold promise as novel high-temperature dielectric substrates for use in flexible printed circuits.

Observation of the liquid metal phase transition in optofluidic microcavities

Gallium (Ga) exhibits remarkable potential in flexible electronics, chemistry, and biomedicine due to its exceptional physical properties. The phase transition and supercooling characteristics of Ga have led to the emergence of numerous valuable applications. In this paper, we capitalize on this foundation by utilizing optofluidic microcavities supporting both high quality factor optical and optomechanical modes to investigate the phase transformation process and supercooling properties of Ga. Our study provides comprehensive insights into the dynamic behavior of Ga during the complete phase transition, such as measuring a hysteresis loop between the solid-to-liquid and liquid-to-solid transitions, revealing nonreciprocal resonance wavelength shift, and identifying a unique metastability state of Ga during melting. The linear thermal expansion coefficients of Ga were precisely measured to be 0.41 × 10−5 K−1 and −0.75 × 10−5 K−1 for solid and liquid Ga, respectively. Our research provides a comprehensive and versatile monitoring platform for newly fabricated liquid metal alloys, offering multidimensional insights into their phase transition behavior.

Research on the improvement of the adhesion strength of the Cu films deposited on the Al2O3 films

Due to the significant discrepancy in the coefficient of linear thermal expansion between Cu and ceramic in T-type thin film thermocouples, the Cu thin films often exhibit a low adhesion strength with the ceramic layers (Al2O3). In order to improve the adhesion strength of the Cu with the Al2O3 films, several methods during preparation were studied. First, different thicknesses of the Cu thin films deposited at different deposition temperatures on the Al2O3 thin films prepared by the magnetron sputtering were studied. Second, the Ti/Ni buffer layer between the Cu and the Al2O3 thin films was prepared. Finally, the average roughness of Al2O3 was studied. The adhesion strength of the Cu with the Al2O3 thin films, the microstructure of the surface and the cross section of the Cu and the Al2O3 thin films, and the grain size and the roughness of the films are characterized by nanoscratch testing, scanning electron microscopy, and atomic force microscopy. The adhesion strength of the Cu films with the Al2O3 films increases with an increase in the thickness of the Cu thin films and the roughness of the Al2O3 thin films and the addition of the Ti/Ni buffer layers.

Influence of fly ash on the properties of wood-polymer composites

This study reports the influence of fly ash on the operational, technological, and physical-mechanical properties of composites based on secondary high-density polyethylene filled with wood flour. It is shown that when calcite is replaced by fly ash in the composite, the operational and technological properties of the material are improved: water absorption, coefficient of linear thermal expansion and technological shrinkage are reduced. When using fly ash as a filler, there is also an increase in the flexural strength of the composite by 9% (from 51.3 MPa in the absence of fly ash to 55.8 MPa in the absence of calcite), but the Charpy impact toughness of samples with cut is decreased by more than 2 times (from 11.9 kJ/m2 to 5.1 kJ/m2, respectively).

Selection of heat treatment and its impact on the structure and properties of AK10M2N–10%TiC composite material obtained via SHS method in the melt

The composite materials based on the Al–Si system alloys, strengthened with a highly dispersed titanium carbide phase, possess improved characteristics and belong to the group of promising structural materials. Currently, self-propagating high-temperature synthesis (SHS) based on the exothermic interaction, wherein titanium and carbon precursors directly involve in the melt, is the most accessible and effective method to obtain them. This paper proves the feasibility and demonstrates the successful synthesis of a 10 wt.% titanium carbide phase in the melt of the AK10M2N alloy, resulting in the AK10M2H-10% TiC composite material. Samples of the matrix alloy and the composite material were subjected to heat treatment according to the T6 mode, with various temperature-time parameters for hardening and aging operations. Based on the results, optimal heat treatment modes were selected to ensure maximum hardness. We studied the macroand microstructure of the obtained samples and performed micro X-ray spectral and X-ray diffraction phase analyses. Different groups of properties underwent comparative tests. It was established that the density of AK10M2N–10%TiC samples before and after heat treatment, according to optimal modes, is close to the calculated value. We showed that the combination of reinforcement and heat treatment significantly increases hardness, microhardness, and compressive strength, with a slight decrease in ductility. Additionally, it maintains the values of the coefficient of thermal linear expansion, high-temperature strength, and resistance to carbon dioxide and hydrogen sulfide corrosion at the level of the original alloy. The greatest effect was observed during the investigation of tribological characteristics: heat treatment of the composite material according to the recommended mode significantly reduces the wear rate and friction coefficient, eliminates seizure and tearing, and prevents temperature rise due to friction heating.

Building and Evaluating a Green and Multifunctional Composite Based on Poly(butylene adipate-co terephthalate) with Zirconium Phosphate and Clove Essential Oil

Although poly(butylene-adipate-terephthalate) (PBAT) is derived from fossil sources, it is classified as a biodegradable polymer because of its predominantly aliphatic ester structure. Synthetic Zirconium phosphate (ZrP) has been widely studied for its notable properties in various fields of human activity. Clove oil (CO) is an eco-friendly material with notable antioxidant and antimicrobial properties. In this context, the present study aimed to develop a green and multifunctional composite based on PBAT incorporated with ZrP, modified ZrP, and CO. The wide-angle X-ray diffraction revealed that the presence of CO promoted the delamination of the phosphates. The thermogravimetric analysis indicated that ZrP and modified ZrP slightly improved the thermal stability of PBAT. The calorimetric evaluations revealed that both ZrP and modified ZrP acted as heterogeneous nucleating agents, increasing the degree of crystallization of PBAT by approximately 70–85%. The incorporation of phosphates and clove oil enhanced the hydrophobicity of the composite films by 20–50%. The thermomechanical analysis indicated a reduction in the glass transition temperature of PBAT and an increase in its linear coefficient of thermal expansion. The type of phosphate and the amount of clove oil influenced the polymer’s molecular relaxation behavior. Antimicrobial testing confirmed that the composite effectively inhibited the growth of Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus) ands the yeast Candida albicans.