Mechanism Of Thermal Expansion Research Articles

Critical Role of Nonrigid Unit and Spiral Acoustical Modes in Designing Colossal Negative Thermal Expansion.

Exploring the relationship between thermal expansion and structural complexity is a challenging topic in the study of modern materials where volume stability is required. This work reports a new family of negative thermal expansion (NTE) materials, AM(CN)4 with A = Li and Na and M = B, Al, Ga, and In. Here, the compounds of LiB(CN)4 and NaB(CN)4 were only synthesized; others were purely computationally studied. A critical role of nonrigid vibrational modes and spiral acoustical modes has been identified in NaB(CN)4. This understanding has been exploited to design the colossal NTE materials of NaM(CN)4 (M = Al, Ga, In). A joint study involving synchrotron X-ray diffraction, Raman spectroscopy, and first-principles calculations has been conducted to investigate the thermal expansion mechanism. It has been found that the A atoms can either increase the symmetry of the crystal structure, inducing stronger NTE, or lower the crystal symmetry, thus resulting in positive thermal expansion. Conversely, the M-site atoms do not affect the crystal structure. However, as the radius of the M atoms increases, the ionic nature of the C-M bonds strengthens and the CN vibrations become more flexible, thereby enhancing the NTE behavior. This study provides new insights to aid in the discovery and design of novel NTE materials and the control of thermal expansion.

A comprehensive investigation on the effect of SiCp on microstructure and mechanical properties of Mg–5Sb-based hybrid composites

Microstructural development, strengthening mechanisms, and mechanical properties of the newly developed Mg–5Sb-xSiCp (x = 0, 1, 3, and 5) composites were studied in both as-cast and extruded states. The microstructures of composites were composed of α-Mg, in-situ Mg3Sb2, and SiCp phases. The cooling curves display that Mg3Sb2 intermetallics form as the primary phase. During solidification, the SiCp acts as heterogeneous sites for both α-Mg and intermetallics formation. The increase in SiCp content (from 0 % to 5 %) modified the as-cast grain size from 827 μm to 411 μm with the improvement of yield strength (YS) (74–97 MPa). Also, the SiC addition to as-cast facilitates the formation of a randomized texture and a significant reduction in intensity from 13.121 mrd to 6.301 mrd for SiC-Free and 5 wt% added MMCs, respectively. Grain refining and recrystallization are characterized by electron backscatter diffraction (EBSD) analysis. Grain refinement via SiCp and hot extrusion leads to substantial structural refinement, resulting in a decrease in grain size from about 411 μm down to 3.92 μm for MMC with 5 wt% of SiC. Consequently, the best combination of the ultimate tensile strength (UTS) (∼244 MPa) and total elongation (∼8.9 %) was obtained for the hot extruded composite containing 3 wt% SiCp. The prevailing strengthening mechanisms are supposed to be particle strengthening mechanism in the as-cast condition and coefficient of thermal expansion (CTE), Orowan, and Hall-Petch mechanisms in the as-extruded condition. Obviously, adding SiCp and employing hot working lead to significant increase in ultimate compressive strength (from 180 MPa to 321 MPa for 5 wt%).

Node Distortions in UiO-66 Inform Negative Thermal Expansion Mechanisms: Kinetic Effects, Frustration, and Lattice Hysteresis.

In metal-organic frameworks (MOFs) the interplay between the dynamics of individual components and how these are constrained by the extended lattice can yield unusual emergent phenomena. For the archetypal Zr-MOF, UiO-66, we explore the cooperative dynamics of a Zr-node transformation that gives rise to negative thermal expansion (NTE). Using in situ synchrotron X-ray scattering, with powder diffraction and pair distribution function (PDF) analyses, we identify lattice hysteresis and a thermal ramp-rate-dependence of the thermal expansion. Specifically, kinetic trapping of distorted node states formed at high temperature, leads to broad variability in the apparent thermal expansion which ranges from large positive to large negative thermal expansion with coefficients of thermal expansion (CTE) from +45 to -80 × 10-6K-1. Time-resolved relaxation studies at selected temperatures suggest that when equilibrated UiO-66 is intrinsically NTE, with a CTE of -35 × 10-6K-1. Kinetic trapping of the node-distorted state following high temperature activation has broad implications for characterization and applications of these Zr-MOFs; the nonequilibrium node state depends on the thermal history of the sample with quench vs slow cooling likely to impact gas binding, pore volume, and accessible catalytic sites.

Enhancing thermal-mechanical performance of micron Ag/ZrW2O8 nanorod die-attach paste with low thermal expansion

Negative thermal expansion not only challenges the traditional lattice concept, but also provides new opportunities for regulating the thermal expansion coefficient and addressing the increasing reliability demands in power device packaging. In this study, ZrW2O8 nanorods were firstly introduced into the micron Ag paste via a facile low-temperature (≤300 ℃) low-pressure (<10 MPa) sintering. The pinning and negative thermal expansion mechanisms contributed by the homogeneously dispersed ZrW2O8 nanorods significantly mitigate the thermal expansion mismatch and suppress the microstructure deterioration in SiC power module, which was also verified by finite element (FE) simulation. The Ag@2%ZrW2O8 (2% of the total weight of Ag) specimen possessed outstanding long-term reliability with a die-shear strength of 29.63 MPa after 1000 thermal shock cycles from −50–250 ℃. The novel findings can be inspiring on interconnected material optimization and selection in electric packaging application as well as reliability evaluation in the service condition.

Use of negative thermal expansion to design scaffolds for cultured meat

Additive manufacturing is proposed as a novel tool to produce complex scaffold constructs for use in cell cultured meat. The presence of scaffolds in the final cell cultured products raises the need to understand the thermal behavior of biopolymers through culturing and cooking as it relates to the final organoleptic properties. Therefore, the objective of this study was to understand how aqueous and high temperature environments influence plasticization and contraction of biopolymer scaffolds through the physio–chemical mechanisms of hydrolysis and negative thermal expansion. To achieve this objective, scaffolds were printed using a negative thermal expansion stretch–dominated design in both PLA and PLA-TPU material configurations. The samples were evaluated after a simulated cooking experiment (90 °C for 10 mins). The formation of crystals in the single material PLA during cooking led to bend–dominated contraction while the dual-material PLA-TPU experienced stretch–dominated contraction. Furthermore, exceeding the glass transition temperature of PLA during simulated cooking in an aqueous environment caused irreversible deformation to the scaffold structure that has the potential to influence organoleptic properties.

Evolution law of pulsating seepage and thermal deformation by injecting high‐temperature steam into coal for thermal coalbed methane recovery

AbstractChinese coal reservoirs are characterized by low pressure and low permeability, which need to be enhanced so as to increase production. However, conventional methods for permeability enhancement can only increase the permeability in fractures, but not the ultra‐low permeability in coal matrices. Attempts to enhance such impermeable structures lead to rapid attenuation of gas production, especially in the late stage of gas extraction. Thermal stimulation by injecting high‐temperature steam is a promising method to increase gas production. The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high‐temperature steam in coal and the thermal deformation of coal. In this study, an experimental approach is developed to explore the high‐temperature steam seepage coupled with the thermal deformation in coal under triaxial stress. The tests were conducted using cylindrical coal specimens of ϕ50 mm × 100 mm. The permeability and thermal strain in coal were investigated when high‐temperature steam was injected at 151.11, 183.20, 213.65, and 239.76°C. The experimental results reveal for the first time that as the amount of injected fluid increases, the steam permeability shows periodic pulsation changes. This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon. When the injected steam temperature increases, the amplitude of pulsating permeability decreases, whereas the frequency increases; meanwhile, the period becomes shorter, the pulsation peak appears earlier, and the stabilization time becomes longer. The average peak permeability shows a “U‐shaped” trend, decreasing first and then increasing as the steam temperature increases. Meanwhile, with the extension of steam injection time, the axial, radial, and volumetric strains of coal show a stage‐wise expansion characteristic at different temperatures of steam injection, except for the radial strains at 151.11°C. A two‐phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam. Moreover, the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted. The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.

Crystal structure solution and high-temperature thermal expansion in NaZr2(PO4)3-type materials.

The NaZr2P3O12 family of materials have shown low and tailorable thermal expansion properties. In this study, SrZr4P6O24 (SrO·4ZrO2·3P2O5), CaZr4P6O24 (CaO·4ZrO2·3P2O5), MgZr4P6O24 (MgO·4ZrO2·3P2O5), NaTi2P3O12 [½(Na2O·4TiO2·3P2O5)], NaZr2P3O12 [½(Na2O·4ZrO2·3P2O5)], and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500°C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr4P6O24 and CaZr4P6O24 was between -1 × 10-6 per°C and 6 ×10-6 per °C from 25 to 1500°C. The crystal structures of the high-temperature polymorphs of CaZr4P6O24 and SrZr4P6O24 with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above ∼1250°C. This work measured thermal expansion coefficients to 1500°C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.

Giant Negative Thermal Expansion in Ultralight NaB(CN)4

AbstractNegative thermal expansion (NTE) is crucial for controlling the thermomechanical properties of functional materials, albeit being relatively rare. This study reports a giant NTE (αV∼−9.2 ⋅ 10−5 K−1, 100–200 K; αV∼−3.7 ⋅ 10−5 K−1, 200–650 K) observed in NaB(CN)4, showcasing interesting ultralight properties. A comprehensive investigation involving synchrotron X‐ray diffraction, Raman spectroscopy, and first‐principles calculations has been conducted to explore the thermal expansion mechanism. The findings indicate that the low‐frequency phonon modes play a primary role in NTE, and non‐rigid vibration modes with most negative Grüneisen parameters are the key contributing factor to the giant NTE observed in NaB(CN)4. This work presents a new material with giant NTE and ultralight mass density, providing insights for the understanding and design of novel NTE materials.

Giant Negative Thermal Expansion in Ultralight NaB(CN)4.

Negative thermal expansion (NTE) is crucial for controlling the thermomechanical properties of functional materials, albeit being relatively rare. This study reports a giant NTE (αV ∼-9.2 ⋅ 10-5 K-1 , 100-200 K; αV ∼-3.7 ⋅ 10-5 K-1 , 200-650 K) observed in NaB(CN)4 , showcasing interesting ultralight properties. A comprehensive investigation involving synchrotron X-ray diffraction, Raman spectroscopy, and first-principles calculations has been conducted to explore the thermal expansion mechanism. The findings indicate that the low-frequency phonon modes play a primary role in NTE, and non-rigid vibration modes with most negative Grüneisen parameters are the key contributing factor to the giant NTE observed in NaB(CN)4 . This work presents a new material with giant NTE and ultralight mass density, providing insights for the understanding and design of novel NTE materials.

Mechanism of Negative Thermal Expansion in Monoclinic Cu2P2O7 from First Principles.

Negative thermal expansion (NTE) materials generally have high-symmetry space groups, large average atomic volumes, and corner-sharing octahedral and tetrahedral coordination structures. By contrast, monoclinic α-Cu2P2O7, which has a small average atomic volume and edge-sharing structure, has been reported to exhibit NTE, the detailed mechanism of which is unclear. In this study, we investigate the A2B2O7 polymorphs and analyze the NTE behavior of α-Cu2P2O7 using first-principles lattice-dynamics calculations. From the polymorphism investigation in 20 A2B2O7 compounds using 6 representative crystal structures, small A and B cationic radii are found to stabilize the α-Cu2P2O7-type structure. We then analyze the NTE behavior of α-Cu2P2O7 using quasi-harmonic approximation. Our calculated thermal expansion coefficients and anisotropic atomic displacement parameters were in good agreement with those of the experimental reports at low temperatures. From the mode-Grüneisen parameter distribution plotted over the entire first-Brillouin zone, we found that the phonon contributing most significantly to NTE emerges not into the special points but between them. In this phonon mode, the O connecting two PO4 tetrahedra rotates, and the Cu and O vibrate perpendicular to the bottom of the CuO5 pyramidal unit, which folds the ac lattice plane. This vibration behavior can explain the experimentally reported anisotropic NTE behavior of α-Cu2P2O7. Our results demonstrate that the most negative mode-Grüneisen parameter contributing to NTE behavior is not always located on high-symmetry special points, indicating the importance of lattice vibration analyses for the entire first-Brillouin zone.

Kinetic- and Strain-Energy Approaches in the Thermal Analysis of Constrained Mechanical Systems: A Comparative Study

Abstract Despite the unconstrained thermal expansion is assumed stress-free, the conventional FE approach requires formulating elastic forces, and this in turn leads to elastic stresses. A displacement-based formulation, on the other hand, can be used to address this limitation by converting the thermal energy to kinetic energy instead of strain energy. The fundamental differences between the strain- and kinetic-energy approaches are discussed. It is shown that the unconstrained thermal expansion predicted using the kinetic-energy approach is independent of the continuum constitutive model, and consequently, such a formulation can be used for both solids and fluids. The displacement (kinetic) and strain (stress) formulations are discussed to shed light on the mechanism of thermal expansion at the macroscopic level. The thermal-expansion displacement formulation (TEDF) and position-gradient multiplicative decomposition into thermal and mechanical parts are used to compute the thermal stresses due to boundary and motion constraints (BMC). TEDF implementation issues are discussed and constant matrices evaluated at a preprocessing stage after applying sweeping matrix technique to eliminate rigid-body thermal-displacement translational modes are identified. Furthermore, the softening effect due to the constitutive-model dependence on the temperature is investigated at high temperatures. Numerical results are presented to show fundamental differences between the TEDF approach that converts heat energy to kinetic energy and conventional FE approach that converts heat energy to strain energy that produces elastic stresses.

Thermal expansion characteristics of high energy insensitive explosive α-NTO

ABSTRACT Thermal expansion is an important structural parameter to evaluate the structural stability and performance reliability of energetic materials. In order to further understand the thermal expansion characteristics and mechanism of high-energy insensitive explosive 3-nitro-1, 2, 4-triazol-5-one (NTO), the thermal expansion characteristics of α-NTO were studied by in-situ X-ray diffraction (XRD) technique. Based on the Rietveld full-spectrum fitting structure refinement principle, the thermal expansion coefficient of α-NTO was obtained. The results show that α-NTO exhibits obvious reversible anisotropic thermal expansion under the action of thermal field. Based on infrared and Raman spectroscopy combined with theoretical calculation methods, the crystal packing structure of α-NTO at different temperatures and its correlation with thermal expansion characteristics were studied. It is believed that the functional groups that produce hydrogen bonds and hydrogen bond receptors in the crystal structure of α-NTO under thermal stimulation play a leading role. At the same time, compared with the thermal expansion characteristics of other explosive crystals, the influence of crystal packing on the thermal stability of explosive crystal structure was analyzed. The results show that the thermal expansion anisotropy of layered packing explosive crystals with strong hydrogen bonding is more obvious.

Revaluating coal permeability-gas pressure relation under various gas pressure differential conditions

Identifying changes in coal permeability with gas pressure and accurately codifying mean effective stresses in laboratory samples are crucial in predicting gas-flow behavior in coal reservoirs. Traditionally, coal permeability to gas is assessed using the steady-state method, where the equivalent gas pressure in the coal is indexed to the average of upstream and downstream pressures of the coal, while ignoring the nonlinear gas pressure gradient along the gas flow path. For the flow of a compressible gas, the traditional method consistently underestimates the length/volume-averaged pressure and overestimates mean effective stress. The higher the pressure differential within the sample, the greater the error between the true mean pressure for a compressible fluid and that assumed as the average between upstream and downstream pressures under typical reservoir conditions. A correction coefficient for the compressible fluid pressure asymptotes to approximately 1.3%, representing that the error in mean pressure and effective stress can be on the order of approximately 30%, particularly for highly pressure-sensitive permeabilities and compressibilities, further amplifying errors in evaluated reservoir properties. We utilized this volume-averaged pressure and effective stress to correct permeability and compressibility data reported in the literature. Both the corrected initial permeability and the corrected pore compressibility were found to be smaller than the uncorrected values, due to the underestimation of the true mean fluid pressure, resulting in an overestimation of reservoir permeability if not corrected. The correction coefficient for the initial permeability ranges from 0.6 to 0.1 (reservoir values are only approximately 40% to 90% of laboratory values), while the correction coefficient for pore compressibility remains at approximately 0.75 (reservoir values are only approximately 25% of laboratory value). Errors between the uncorrected and corrected parameters are quantified under various factors, such as confining pressure, gas sorption, and temperature. By analyzing the evolutions of the initial permeability and pore compressibility, the coupling mechanisms of mechanical compression, adsorption swelling, and thermal expansion on the pore structure of the coal can be interpreted. These findings can provide insights that are useful for assessing the sensitivity of coal permeability to gas pressure as truly representative of reservoir conditions.

Thermal Expansion of Fedotovite K2Cu3O(SO4)3 and Piypite K4Cu4O(SO4)4·(Na,Cu)Cl

This paper presents the results of a study of the thermal behavior of fedotovite K2Cu3O(SO4)3 and piypite K4Cu4O(SO4)4∙(Na,Cu)Cl minerals in a wide temperature range. The crystal structure of the holotype piypite specimen is refined at room temperature. The mechanisms of thermal expansion of minerals depending on the crystal structure are described.

Simulation of the N-MFSK Method Used for Laser-Induced Acoustic Communication

Laser-induced acoustic (LIA) technology is a possible way of communicating from an air platform to an underwater target. The present paper describes a modulation method of n-multiple frequency shift keying (n-MFSK) used for improving the communication rate of LIA technology. The thermal expansion mechanism was selected as a way of generating an acoustic signal by the pulse laser in this work. Thus, the technology of pulsed repetition frequency (PRF) can be used to realize n-MFSK modulation by controlling laser frequency and allocating periods in the time domain. The results of numerical simulation show that n-MFSK modulation can improve the communication rate and band utilization compared with the traditional n-frequency shift keying (n-FSK) modulation.

Control of Thermal Expansion in TaVO5 by Double Chemical Substitution.

The control of thermal expansion is an important and challenging issue. Focusing attention on the class of AMO5 negative thermal expansion (NTE) materials, an approach to control their thermal expansion is still missing. In this work, the thermal expansion of TaVO5 has been controlled from strong negative to zero to positive by double chemical substitution, i.e., Ti and Mo replace Ta and V elements, respectively. A joint study of temperature-dependent X-ray diffraction, X-ray photoelectron spectroscopy, and first-principles calculations has been performed to investigate the thermal expansion mechanism. With the increasing substitution of Ti and Mo atoms, the valence state always remains balanced, and the volume decreases together with a lattice distortion, which leads to the suppression of the NTE. Lattice dynamics calculations confirm that the negative Grüneisen parameters of the low-frequency modes weaken and the thermal vibrations of the polyhedral units diminish after the substitution of Ti and Mo atoms. The present work successfully achieves a tailored thermal expansion in TaVO5 and draws a possible way to control the thermal expansion of other NTE materials.

Effect of equal channel angular pressing on the mechanical properties of homogenized hybrid AZ61 magnesium composites

This study addressed the development and investigation of an AZ61 hybrid composite (HBC) fabricated by the stir casting method followed by equal channel angular pressing (ECAP). The HBC was reinforced using both Al 2 O 3 and SiC nanoparticles. The microstructural examination showed that the introduced reinforcements broke down the round-like formed precipitates into needle-like shapes that enhanced the ductility. Furthermore, the grain size of the HBCs is highly reduced while increasing the number of ECAP passes due to dynamic recrystallization (DRX). The obtained mechanical properties showed that the optimal yield strength (YS), ultimate tensile strength (UTS), and elongation were observed in the AZ61+2%Al 2 O 3 +1%SiC hybrid composite after two passes of ECAP. The Hall Petch strengthening mechanism was primarily responsible for the improved mechanical properties of AZ61 HBC, jointly with the mutual contribution of several mechanisms, including the coefficient of thermal expansion, Orowan looping, and load transfer mechanisms. • AZ61/Al2O3/SiC hybrid composite was produced by stir casting followed by ECAP. • Due to dynamic recrystallization, grain size was highly reduced during ECAP. • The mechanical characteristics of HBC enhanced after the each ECAP pass.

Ferroelastic tetragonal-monoclinic phase transition and anisotropic thermal expansion of LuNbO4 ceramics

Rare-earth tantalates (RETaO4) and niobates (RENbO4) are widely studied as promising thermal barrier coatings based on the ferroelastic tetragonal-monoclinic (t-m) phase transition. We studied the t-m transition process, anisotropic thermal expansion coefficients (TECs), and the corresponding spontaneous strain of LuNbO4 by powder high-temperature X-ray diffraction. The results proved that the unit cell volume and TECs continuously increased with increasing temperature, and the dominant mechanisms of thermal expansion were proposed. Two different orientation states (S1 and S2) caused by the t-m transition led to formation of the ferroelastic domains, and the corresponding spontaneous strain was determined. The relationship between the t-m transition and spontaneous strain was proposed for further property tailoring. This work provided an in-depth analysis of the ferroelastic t-m phase transition, and it would advance the applications of ferroelastic ceramics.

Crystal growth and negative thermal expansion properties of a Y2Mo4O15 single crystal.

A bulk-size single crystal of Y2Mo4O15 with 20 × 11 × 8 mm3 was successfully grown by the top-seed solution growth (TSSG) method. The full-width at half maximum of (100) and (010) crystal faces is 37 and 27 arcsec, respectively. The thermal conductivity coefficients κ 11, κ 22, κ 33, and κ 13 are determined to be 1.519, 2.097, 0.445, and 0.997 W m-1 K-1, respectively. It is worth noting that the Y2Mo4O15 crystal shows significant anisotropy thermal expansion properties, which exhibits a negative thermal expansion along the b-axis (α 22 = -5.11 × 10-6 K-1). The crystal structure analysis shows that the shrinking of Mo-O bond lengths along the b-axis with the increasing temperature would be the main origin of the negative thermal expansion properties for Y2Mo4O15 crystal, which does not comply with the current mechanism.

Significant Zero Thermal Expansion Via Enhanced Magnetoelastic Coupling in Kagome Magnets.

Zero-thermal-expansion (ZTE) alloys, as dimensionally stable materials, are urgently required in many fields, particularly in highly advanced modern industries. In this study, high-performance ZTE with a negligible coefficient of thermal expansion av as small as 2.4ppm K-1 in a broad temperature range of 85-245 K is discovered in Hf0.85 Ta0.15 Fe2 C0.01 magnet. It is demonstrated that the addition of trace interstitial atom C into Ta-substituted Hf0.85 Ta0.15 Fe2 exhibits significant capability to tune the normal positive thermal expansioninto high-performance ZTE via enhanced magnetoelastic coupling in stabilized ferromagnetic structure. Moreover, direct observation of the magnetic transition between ferromagnetic and triangular antiferromagnetic states via Lorentz transmission electron microscopy, along with corresponding theoretical calculations, further uncovers the manipulation mechanism of ZTE and negative thermal expansion. A convenient and effective method to optimize thermal expansion and achieve ZTE with interstitial C addition may result in broadened applications based on the strong correlation between the magnetic properties and crystal structure.