Volume Thermal Expansion Research Articles

First-principles calculations on electronic, superconducting, mechanical, and thermodynamic properties for the superhard compound Tc2C under pressure

This study presents a theoretical investigation on the electronic, superconducting, mechanical, and thermodynamic properties of the superhard compound Tc2C up to 100 GPa. The investigation is conducted via the first-principles plane-wave pseudopotential method. Furthermore, to treat the exchange-correlation potential for the total energy calculations, the revised Perdew–Burke–Ernzerhof formulation stemming from the generalized gradient approximation is employed. The results suggest that Tc2C is a potential hard compound due to the robust covalent bonding between Tc and C atoms. Moreover, the electronic structure and electron–phonon coupling reveal that Tc2C is a superconducting material with Tc of 0.59 K at 0 GPa. Additionally, using the quasi-harmonic Debye model, the variation of crucial structural parameters, such as the volume thermal expansion coefficient, heat capacity, and isothermal bulk modulus and its pressure derivatives, is predicted in terms of temperature and pressure. The results demonstrate that temperature and pressure have contrasting effects on the volume thermal expansion coefficient and heat capacity, and the effect of temperature is larger than that of pressure, especially at low temperatures. The isothermal bulk modulus decreases with increasing temperature but increases with increasing pressure. The first and second pressure derivatives of the isothermal bulk modulus for Tc2C are not the assumed constants in the equation of state study at high pressures and temperatures. To our knowledge, this study presents the first quantitative theoretical prediction of the pressure and temperature dependence of the thermodynamic parameters for Tc2C, which is essential for understanding the basic physical properties of similar transition metal carbides.

Ab initio investigation of structural, elastic, and thermodynamic characteristics of tetragonal XAgO compounds (X = Li, Na, K, Rb)

The present research utilizes ab initio computations to examine the thermodynamic, structural, and elastic characteristics of XAgO ternary oxides, where X signifies Li, Na, K, and Rb.The GGA-PBE and GGA-WC functionals were used to calculate the ground-state lattice parameters and atomic position coordinates of the title materials. The calculated results were in good agreement with both experimental measurements and theoretical predictions. This suggests that the GGA-PBE and GGA-WC functionals are accurate for describing the structural properties of the material under study.This study offers computational predictions for the elastic properties of monocrystalline structures and polycrystalline aggregates of XAgO compounds. These predictions encompass various key parameters, including single-crystal elastic constants, Young’s modulus, bulk modulus, Lame coefficients, Poisson’s ratio, shear modulus, and Debye temperature. Additionally, the quasi-harmonic Debye approximation is utilized to explore the temperature-dependent behavior of bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities over an extensive temperature range, while maintaining constant pressures. The results obtained from this model are found to be highly successful in accurately predicting the behavior of these properties.

Volume thermal expansivity for diatomic ionic solids at high pressures and high temperatures

Volume thermal expansivity for Lif, NaF, KF, RbF and MgO have been determined using the Chopelas–Boehler approximation for the volume dependence of the Anderson-Grüneisen parameter. Expressions have been derived analytically for the thermal expansivity, pressure-volume-temperature relationship, interatomic distances and bulk modulus by developing a modified version of the Liu model. The calculated values for various properties are discussed and compared with the available experimental data and theoretical results reported in the literature.

Macro-encapsulation of metallic phase change materials with sacrificial density less than 3.5 % for medium-temperature heat storage

To solve the problems of volume thermal expansion and high chemical activity of metallic phase change materials (PCMs), this paper successfully prepared millimeter/centimeter-size durable Bi@Void@Kaolin macrocapsules. Fortunately, carbon powder clusters from the thermal decomposition of adhesive CMC gathered on the core PCMs, cleverly adding a reducing atmosphere into the capsules. In particular, the buffer voids of macrocapsules were created from the pores and gaps between the accumulated Bi powders, and the method of improving the bulk density of powder cores as core precursors by the cold isostatic pressing (CIP) technology solves the problem of excessive cavity volume. Thermal analysis indicates that after CIP treatment, the heat storage density of the Bi@Kaolin macrocapsule with the unpressurized powder core volume accounting for 50% can be increased by 18.4%–275.0 J/cm3, which is about 2.5 times the heat storage density of the common medium-temperature heat storage materials - concrete and NaCl, under the working temperature range of 240–300 °C. Solid-liquid PCMs need to sacrifice their density in exchange for the necessary cavity volume, therefore the “actual volumetric heat storage density” of PCMs should be specified. The results show that the proportion of sacrificial density of Bi PCM (i.e. the cavity rate of Bi-based macrocapsule) can reach the optimal value of 3.5%, its actual volumetric heat storage density can reach 558.9 J/cm3 at 240–300 °C. Surprisingly, all the Bi@Kaolin macrocapsules showed excellent cycling durability and thermal stability during 500 cycles under air atmosphere and subsequent 24 h overload-temperature oxidation tests.

Influence of A/B Element Substitution on Negative Thermal Expansion in AB(CN)6 (A = Al, Ga, In; B = Co, Fe, Mn, Cr, V, Ti): A Density Functional Theory Study.

Negative thermal expansion as an abnormal physical behavior of materials has promising applications in a high sophisticated equipment field, but the materials are rare. Here, we use the first-principles calculations based on density functional theory combined with the recently developed average atomic volume (AAV = V/N, where V is unit cell volume and N is the number of atoms in the unit) rule to predict the large isotropic negative thermal expansion materials of Prussian blue analogues AB(CN)6 (A = Al, Ga, In; B = Co, Fe, Mn, Cr, V, Ti) in a wide temperature range. Our results clearly show that the coefficient of negative thermal expansion has a near-linear relationship with the average atomic volume of the systems and is also influenced by the element substitution at the A or B site. Lattice dynamic simulations indicate that the main contribution to the negative thermal expansion comes from the low-frequency transverse vibration of the (B)-C≡N-(A) groups, especially the transverse vibration of the N atoms. Thus, the element substitution at the A site (binding to N) can tune the negative thermal expansion behavior of the systems more effectively than that at the B site (binding to C), indicating the different roles of bonds on the negative thermal expansion. Our present work not only expands the kinds of isotropic materials but also gives some insights into the relationship between the average atomic volume and negative thermal expansion.

Zero thermal expansion in Cs2W3O10

Zero thermal expansion materials are important for the practical applications due to their shape stability as changing temperature. The reported concept of average atomic volume is an available method to hunt new zero thermal expansion materials. Here, according to this concept, a tetragonal tungstate Cs2W3O10 with zero expansion has been found. There is no structure phase transition as increasing temperature from 150 K to 573 K. The coefficient of thermal expansion of axes and volume are αa = 0.0074 × 10−6 K−1, αc = 1.63 × 10−6 K−1, and αV = 1.60 × 10−6 K−1, respectively, in the temperature range of 150 ∼ 573 K. The temperature- and pressure-dependent Raman spectra reveal that the vibrations of WO6 octahedra libration modes with positive total anharmonicity and W-O-W bending mode with negative Grüneisen parameter are possibly the origin of zero thermal expansion in Cs2W3O10.

Unconventional electronic phase transition in SnBi2Te4: role of anomalous thermal expansion.

We propose SnBi2Te4to be a novel topological quantum material exhibiting temperature (T) mediated transitions between rich electronic phases. Our combined theoretical and experimental results suggest that SnBi2Te4goes from a low-Tsemimetallic phase to a high-T(room temperature) insulating phase via an intermediate metallic phase. Single crystals of SnBi2Te4are characterized by various experimental probes including synchrotron based x-ray diffraction, magnetoresistance, Hall effect, Seebeck coefficient and magnetization. X-ray diffraction data confirms an anomalous thermal expansion of the unit cell volume below ∼100 K, which significantly affects the bulk band structure and hence the transport properties. Simulated surface states are found to be topologically robust with varyingT. This indirectly supports the experimentally observed paramagnetic singularity in the entireT-range. The proposed coexistence of such rich phases is a rare occurrence, yet it facilitates a fertile ground to tune them in a material driven by structural changes.

Pickering phase change slurries

HypothesisPhase change slurries (PCS) have emerged as a promising class of oil-in-water emulsions for energy applications, but stability remains an issue. Pickering phase change slurries (PPCS) stabilized solely by nanoparticles could offer enhanced stability. We hypothesize that stability in PPCS can be achieved by tuning environmental variables of salinity and temperature. ExperimentsA paraffin-based PPCS stabilized using fumed silica nanoparticles was developed and assessed under varying NaCl concentrations (up to 150 mM) and temperatures (up to 70 °C). Extended-DLVO modeling, confocal, and cryogenic electron microscopy analyzed the silica-paraffin interactions. Rheological experiments examined the impact of effective volume fraction, thermal expansion, and salinity on the viscosity and shear stability of PPCS. The stability of the resulting formulation was assessed under high pressure and temperature conditions. FindingsIncreased salinity did not change the packing density of the silica at the oil–water interface (82% ± 6%) but did increase the adsorbed layer thickness and network formation, enhancing the formulation's resistance to shear-induced instability. A critical volume fraction of 0.51 ± 0.01 was identified, beyond which viscosity increased significantly. The resulting formulations remained stable under high pressures and temperatures, regardless of salinity. These findings offer insights into the variables affecting PPCS properties, assisting in designing stable PPCS formulations for diverse applications.

Tribo-mechanical, physical and thermal behaviour of Al/Si3N4 composite with and without the addition of Cu, Ni and Cr entropy elements

In the present investigation, a comparative study has been presented between Al/Si3N4 and entropy elements (Cu, Ni and Cr) mixed Al/Si3N4 composite material. The investigation revealed that the tensile strength and hardness of base material were enhanced by 23.65% and 56.66% respectively with an increase of 10 wt. % of Si3N4. The tensile strength of Al and Al/10 wt. % Si3N4 composite was enhanced by 46% and 18% respectively after the addition of entropy elements 1.5 wt. % Cu, 1.5 wt. % Ni and 1 wt. % Cr. Further, the same wt.% of entropy elements enhanced the hardness of Al and Al/10 wt. % Si3N4 composite by 83.66% and 27%, respectively. The ductility and toughness of the composite were further improved by adding the 1.5 wt. % Cu, 1.5 wt.% Ni and 1 wt.% Cr in Al/10 wt. % Si3N4 composite. However, corrosion weight loss, volume thermal expansion and wear of the composite are reduced by adding the entropy elements. The number of grains per square inch for Al/10 wt% Si3N4 composite with and without adding the 1.5 wt. % Cu, 1.5 wt.% Ni and 1 wt.% Cr was found to be 3590.57 and 2385.37, respectively. The addition of entropy elements results in a finer grain structure of the composite which shows grain refinement.

First-principles calculation of Fe-Mo-Cr alloys based on special quasi-random structure

Mo element has an important effect on ferritic stainless steel. It is of great significance to study the role of the Mo element in the composition design of stainless steel alloys. In this paper, the formation energy, magnetic moment, electronic structure, mechanical and high-temperature mechanical properties of Fe-Mo binary alloys and Fe-Mo-Cr ternary alloys were obtained by density functional theory of first principles. The results showed that the formation energy increases gradually with the increase of Mo content. The alloys have a stable system when the Mo concentration is less than 3.125%. The addition of Cr increases the formation energy, but when Mo content is 3.125%, the formation energy is lower than that of Fe-Mo binary alloys. Fe atoms are ferromagnetic state and Mo atoms are anti-ferromagnetic state, there is an opposite magnetic effect between them. With the increase of Mo concentration, Mo atoms change from anti-ferromagnetic to paramagnetic. Mo atoms become paramagnetic when Mo concentration reaches 100%. Mo element has little effect on the shear modulus of the alloys. The hardness and compressive strength decrease with increasing Mo concentration. The addition of Cr atom also reduces the hardness. Fe-Mo alloys have better thermal stability when Mo concentration is 12.5%. The Cr atom significantly changes the thermodynamic properties of the alloys. The volume thermal expansion coefficient of Fe-Mo-Cr ternary alloys decreases with the increase of Mo concentration, and the highest temperature appears near the Mo concentration of 12.5∼18.75%.

Reduced Gravity and Magnetohydrodynamic Effects on Transient Mixed Convection Flow Past a Magnetized Heated Cone Embedded in Porous Medium

The effects of reduced gravity on the periodic behavior of convective heat transfer characteristics of fluid flow along the magnetized heated cone embedded in porous medium is studied in the current contribution. The mathematical form of the nonlinear partial differential equations subject to the boundary conditions for the proposed unsteady model is presented. By employing appropriate dimensionless quantities, the mathematical equations are transformed into dimensionless form to get the numerical solutions of the proposed model. The dimensionless form is further condensed to a form that is more straightforward for smooth numerical computations. Later, large simulations are run using the implicit finite difference method for appropriate range of parameters values included in the flow model. The effect of reduced gravity parameter R g , the Richardson parameter or mixed convection parameter λ , the Prandtl number Pr, and the porosity parameter Ω , on chief physical quantities, that is, velocity profile, temperature distribution, magnetic intensity, transient skin friction, transient rate of heat transfer, and transient current density are simulated and highlighted graphically. Additionally, via careful examination and intentional discussion of physical reasoning, the physical impacts of various factors on the material qualities are examined. Applications that motivate the present work is the reduced gravity effects due to which the other nongravity forces such as thermal volume expansion, density difference, and magnetic field can induce the fluid motion.

A Low-Density Polyethylene-Reinforced Ternary Phase-Change Composite with High Thermal Conductivity for Battery Thermal Management

Paraffin phase change materials (PCMs) exhibit great potential in battery thermal management (BTM); nevertheless, their application has been hampered by the handicap of low thermal conductivity, leakage, and volume expansion during phase transition. In this work, ternary composite PCMs formed of paraffin, expanded graphite (EG), and low-density polyethylene (LDPE) were developed for application in BTM. The structure and properties of the composite PCMs were characterized via X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and thermal constant analysis. The result shows that EG can form a large-size graphite frame as heat conduction paths to improve the thermal conductivity of the composite PCM, and LDPE can form an interpenetrating network within the composite PCM to resist the internal stress of paraffin expansion and prevent deformation. The latent heat and thermal conductivity of the composite PCMs loaded with 10 wt% EG and 4 wt% LDPE can reach 172.06 J/g and 3.85 Wm−1K−1 with a relatively low leakage ratio of 6.2 wt%. Remarkably, the composite PCMs could reduce the temperature rise of the battery by 55.1%. In brief, this work provides a feasible route to develop high-performance PCMs for BTM.

Thermal and stress-strain state of friction pairs in ventilated disc brakes of lightweight vehicles

The work is dedicated to the thermal behavior and stress-strain state of ventilated disc brakes installed in the lightweight vehicles (scooters, electric bikes, ATVs, etc.) using ANSYS environment in various experiment modes. Modeling of the temperature distribution in the rotor (disc) and the corresponding brake pads is determined taking into account a number of factors and input parameters during the braking operation: the amount of rotation speed, the gap between the pads and the disc, the speed of load application, thermal expansion, etc. Numerical modeling of the transient thermal and the stress fields in the area of contact between the pads and the rotor is carried out by the method of sequential thermostructural connection of the intermediate calculation states of the brake model in the ANSYS Coupled Field Transient environment. For a comprehensive assessment of brake behavior, our research considers two load approaches: constant long-term (20 s) with an influence factor in the form of thermal expansion as a result of contact pair friction; linear load from the pads on the disс with a corresponding increase in pressure up to the moment when the rotation of the system is blocked. Our research presents an assessment of the rotor ventilation channels influence on the nature of the contact spot with the brake pads (open far-field contact, sliding contact, sticking contact, etc.). In addition, it is demonstrated that despite the linear increase in pads pressure on the rotor, the graphs of temperatures, volume (thermal expansion) and stresses are of parabolic character with a disproportionate increase in indicators. Such a result forces us to come to the conclusion that it is not possible to predict the behavior of the brakes based on the analysis during a short period of time of the experiment - conducting long-term analytical studies is extremely important in the case of brakes

Revealing the promising near-room-temperature thermoelectric performance in Ag2Se single crystals

With high carrier mobility and intrinsic low lattice thermal conductivity, Ag2Se compounds have attracted increasing attention for thermoelectric application near room temperature. Due to its phase transition at ∼406 K and resulting thermal volume expansion, the growth and thermoelectric properties of large-sized Ag2Se single crystals have seldom been reported so far. In this work, the vertical Bridgeman method was used for growing bulk Ag2Se single crystal, with an orientation preference along low-symmetric (201) plane. The Hall mobility as high as 2 000 cm2/(V·s) and weak electron-phonon coupling contributes to a high electronic quality BE of ∼7.0 in near-room-temperature β-Ag2Se single crystals, which is superior to the high-temperature phase α-Ag2Se. The observed low lattice thermal conductivity of 0.8 W/(m·K) at 300 K is due to the low group speeds and strong anharmonicity. A promising peak zT of 0.66 at 375 K and an average zT of 0.65 at 300–375 K were realized in β-Ag2Se crystals. The low Vickers hardness and good ductile properties were confirmed by experiment and theoretical analysis. This work not only synthesized large-sized and highly-orientated Ag2Se crystals, but also revealed its great potential of thermoelectric performance and mechanical properties for various applications near room temperature.

The thermal and mechanical properties of Li-based Half Heusler alloys LiAlZ(Z = Si, Ge) using Quasi-Harmonic Approach

Using the Density Functional Density (DFT) method coupled with a Quasi-Harmonic Approximation (QHA), we studied the structural stability and thermal properties of Li-based Half Heusler alloys LiAlZ (Z= Si and Ge). The obtained results show that type I for both compounds is the most stable of all the examined structural phase types i (i = I, II, III) and have semiconductor behavior with narrow indirect band gaps. The study of the elastic constants and phonon curves confirmed that these compounds are mechanically and dynamically stable. The obtained results of total free energy are considered while estimating the thermal properties as the lattice parameters, volume thermal expansion, heat capacity, electronic and entropy in the range of temperature from 0 K to 1000 K. The thermal properties show that half Heuslers LiAlZ are thermodynamically stable, and the vibrational contribution is dominant compared to configurational and electronic contributions in the heat capacity and entropy. In contrast, the vibrational contribution is very small to the configurational and electronic free energy contributions.

Development of over 3000 cycles durable macro-encapsulated aluminum with cavity by a sacrificial layer method for high temperature latent heat storage

The high-temperature metallic phase change materials (PCMs) are attracting great attentions as alternatives to sensible heat storage materials in thermal energy storage (TES) systems. However, the high corrosivity, easy leakage and oxidation phenomena of metallic PCMs have limited their applications. This work reports a facile and novel sacrificial layer method with the purpose to create macro-encapsulating aluminum (Al) PCM by alumina (Al2O3) shell characterized by a ‘buffer’ inner cavity. The inner cavity could offer buffer space to accommodate the huge thermal volume expansion of Al core PCM during heating and melting, thereby preventing the breakage of the capsules and ensuring the long-term stability. A series of Al balls with diameters of 4–25 mm were firstly coated with paraffin sacrificial layer then by Al2O3 dough shell, which was finally conducted by the two-step heat treatment, in which a low-temperature stage aimed at removing the paraffin layer while the high-temperature stage aimed at the capsule sintering formation. The final macrocapsules with diameters of 6.5–31.5 mm were obtained, in which the capsules with Al core balls larger than 15 mm showed superior gravimetric and volumetric heat storage density because of their high core–shell ratio. For example, the 25 mm@0.75 mm@2.5 mm macrocapsules could present high heat storage density of 348 kJ/kg and 902 J/cm3 at the temperature range of 600–700 °C. The macrocapsules also showed a long-time thermal cycling stability, since that no damage or leakage was observed over 3000 times of melting and solidification under air atmosphere, indicating that they can be used over 8 years without any degradation of thermophysical properties. This demonstrates the potential application of the Al2O3 encapsulated Al macrocapsules with inner cavity in high-temperature TES systems.

Neutron diffraction study on anomalous thermal expansion of CrB2

Thermal expansion is an essential issue in the field of materials science and engineering. Investigation of anomalous thermal expansion is beneficial to controlling it and developing related functions. Here, we report disitinctly anisotropic thermal expansion of CrB2 via temperature dependence of neutron diffraction, in which positive thermal expansion is observed within basal plane whereas negative thermal expansion emerges along the c direction. Intriguingly, zero thermal expansion of unit cell volume is determined from 5 to 130 ​K with the coefficient of thermal expansion of ᾱV ​= ​0.4(1) ​× ​10−6 ​K−1. Magnetization measurement shows there is an antiferromagnetic-paramagnetic transition near 90 ​K, which may correlate to the thermal expansion anomaly. DFT calculations identify no chemical binding of Cr–Cr pair, implying such antiferromagnetic ordering originates from the double exchange interaction of Cr–B–Cr.

Thermodynamic measurements and ab initio calculations of the indium-lithium system

The limiting enthalpy of the solution of liquid indium in liquid tin was measured at 723 K. The calorimetric method was applied to determine the standard enthalpy of the formation of intermetallic phases and alloys from the In-Li system. The measurements were done at 747 K and 756 K. The structures of prepared alloys were confirmed by the X-ray diffraction measurements. Besides that, the ab initio calculations allowed the modeling of the formation energies, the volume thermal expansion, the heat capacity under constant pressure, and the elastic properties of the intermetallic phases. The theoretical formation energies show good agreement with the experimental findings. The analysis of the phonon dispersion indicates an instability of the InLi phase in the Fd-3m space group. A further investigation on the atomic arrangement in the case of the equiatomic ratio is suggested.

Effects of pressure and temperature on topological electronic materials X2Y3 (X = As, Sb, Bi; Y = Se, Te) using first-principles.

We systematically study the thermal and topological properties of X2Y3 (X = As, Sb, Bi; Y = Se, Te) and the effects of pressure and temperature on their electronic properties using first-principles. We find that the external pressure-induced electronic topological transition occurs at about 5 GPa for Bi2Se3, and the type of band gap tends to become indirect with the increase of pressure. We also investigate the lattice expansion with temperature in quasi-harmonic approximation and further explore the effect of temperature on the volume, band gap, and volumetric thermal expansion coefficient of the studied selenides and tellurides. Finally, we calculate the evolution of the Wannier charge center of X2Y3 to determine their topological invariants, and theoretically suggest that Bi2Se3 changes from a topological to an ordinary insulator when the pressure decreases to -8 GPa; As2Se3 is found to be an ordinary insulator, while all other four compounds are always strong topological insulators at any pressure or temperature.

Cohesive and Thermal Properties of Sodium Cyanide-Halide Mixed Crystals

In order to analyse the cohesive and thermal properties of sodium cyanide-halide mixed crystals an Extended Three Body Force Shell Model (ETSM) has been applied by incorporating the effect of translational-rotational (TR) coupling. We have conducted theoretical research on cohesive and thermal properties, such as cohesive energy (, molecular force constant (f), compressibility (), Restrahlen frequency (, Debye temperature (D), Gruneisen parameter (), Moelwyn Hughes constants (F1) and the ratio of volume thermal expansion coefficient (v) to volume specific heat (Cv), as a function of temperature within the temperature range 50K T 300K at concentration x=0, 0.27, 0.58 and 1. The current model computations and the findings of the available experiments are in good agreement. The ETSM is a sufficiently realistic model and may be applied to a variety of other mixed crystals in this family.