Volumetric Thermal Expansion Coefficient Research Articles

Heat flow visualization of a chemical compound isobutane (C4H10) past a vertical cylinder in the subcritical, near critical and supercritical regions

Supercritical fluids (SCF's) found to have a large number of applications in science and engineering field particularly in separation and purification, green technologies etc. The present research paper investigates the heatline visualization of unsteady free convection supercritical fluid flow over a vertical cylinder using Bejan's heat function concept by using isobutane as a model compound. A new thermodynamic equation has been obtained to calculate the volumetric thermal expansion coefficient (β) based on the Redlich-Kwong equation of state (RK-EOS), in order to determine the free convection properties of isobutane in supercritical fluid (SCF) region. In this model the thermal expansion coefficient is characterized as a function of compressibility factor, temperature and pressure. Crank-Nicolson type of implicit finite difference method is utilized to obtain the results in terms of the streamlines (ψ), isotherms (θ) and heatlines (Π) for the different values of reduced temperature and reduced pressure in the SCF region. The numerically calculated thermal expansion coefficient values are validated with existing experimental results. Numerical simulations are performed for isobutane in three regions namely, subcritical, near critical and supercritical regions. The unsteady boundary layer flow analysis shows that the streamlines are beginning from the leading edge to the far downstream, whereas the heatlines ends at a finite distance from the surface of cylinder. The non-dimensional values of heat function are closely associated with the overall heat transfer rate. The SCF flow analysis implies that in the vicinity of the hot cylindrical surface the heatlines are observed to be denser. Further, the deviation of streamlines, isotherms and heatlines from the hot cylindrical surface increases as reduced temperature and reduced pressure increases.

Exploring the intrinsic ductile metastable Fe-C compounds: Complex chemical bonds, anisotropic elasticity and variable thermal expansion

As the vitally important phases in iron and steel, the Fe-C binary compounds are investigated by first-principles calculations combined with quasi-harmonic approximation (QHA). The formation enthalpy and Gibbs free energy are positive, but the phonon dispersion are stable, indicating θ-Fe3C, o-Fe7C3, h-Fe7C3, γ-Fe23C6, χ-Fe5C2, η-Fe6C, η-Fe2C and ε-Fe3C are metastable phases in this binary system for the first time. The electronic structure indicates that the complex bonding behavior of these carbides are the combinations of covalent, ionic and metallic bonds, which determines the anisotropic elastic properties and novel intrinsic ductility of these carbides. The mechanical modulus is nearly proportional to the carbon content. o-Fe7C3 has the largest B value as 379 GPa and The anisotropic bulk modulus, shear modulus and Young's modulus are discussed by the anisotropic index and three-dimensional surface contours. The shear modulus range from 40 GPa to 204.2 GPa and the Young's modulus vary from 113.7 GPa to 512.6 GPa. Intrinsic hardness is predicted by semiempirical models. The thermal electronic contributions to thermodynamic properties are studied using the Mermin statistics for the dynamic stable phases. The volumetric thermal expansion coefficients of these Fe-C compounds vary between 1.0 × 10−5 K−1 to 5.0 × 10−5 K−1 at 1200 K. θ-Fe3C, h-Fe7C3 and η-Fe2C have the closest thermal expansion coefficient to α-Fe. Considering the thermal electronic contribution, the calculated heat capacity of θ-Fe3C is in good agreement with experimental results. η-Fe2C has the largest CP value as 0.72 J g−1 K−1 and η-Fe6C has the smallest CP value as 0.56 J g−1 K−1 at 1200 K.

Phase transition and thermoelastic behavior of cadmium sulfide at high pressure and high temperature

The phase transition and thermal equation of state of cadmium sulfide (CdS) were studied at high pressure and temperature conditions up to 21.9 GPa and 650 K, by using in situ synchrotron angle-dispersive X-ray diffraction and an externally-heated diamond anvil cell (DAC). A pressure-induced phase transition from wurtzite structure (WZ) to rocksalt structure (RS) was observed at about 2.6 GPa, which was agreed with previous studies (2.0–3.5 GPa). In addition, fitting of the experimental data by means of the third-order Brich-Murnaghan equation of state (III-BM EoS) gives the bulk modulus K0 = 81.6 (13) GPa, its pressure derivative K′0 = 3.68 (13), and the volumetric thermal expansion coefficient α0 = 2.97 (25) × 10−5 K−1 for RS phase of CdS. Simultaneously, the thermal expansion coefficient (α0 = 1.51 × 10−5 K−1), and its axial thermal expansivities (8.30 × 10−6 K−1 and 5.96 × 10−6 K−1) along a-axis and c-axis for WZ phase of CdS at ambient conditions were obtained, respectively. Moreover, it was found that the phase transition pressure from WZ (or ZB) type to RS type of cadmium chalcogenides (CdS, CdSe and CdTe) is quite similar by comparing their phase transition pressures. Furthermore, the elastic properties of metal sulfides (ZnS, CdS, HgS, PbS) with the same crystal structure but different metal cations were also discussed, and found that the bulk moduli for the RS phase of metal sulfides (ZnS, CdS, HgS, PbS) have a negative correlation with the cation radius, but a positive correlation with the electronegativity.

Erratum to: “Volumetric Thermal Expansion Coefficients of the Equiatomic Na–K and K–Rb Melts” [Russian Metallurgy (Metally), vol. 2017, no. 8, pp. 625–626

Erratum to: “Volumetric Thermal Expansion Coefficients of the Equiatomic Na–K and K–Rb Melts” [Russian Metallurgy (Metally), vol. 2017, no. 8, pp. 625–626

Combined experimental and ab initio based determination of the thermal expansion of La0.5Sr0.5Co0.25Fe0.75O3

AbstractThe thermal expansion of La0.5Sr0.5Co0.25Fe0.75O3 (LSCF55) is investigated both by first principles phonon calculations combined with the quasi‐harmonic approximation (QHA) and by experimental approaches. Within the framework of the QHA, the volumetric thermal expansion coefficient of rhombohedral LSCF55 is calculated as αV,GGA = 50.34 × 10−6 K−1. For comparison, the lattice expansion and the volume expansion of LSCF55 grain are measured by in situ high‐temperature X‐ray diffractometer (HT‐XRD). An anisotropic thermal expansion of rhombohedral LSCF55 with αa,hex = 10.89 × 10−6 K−1 and αc,hex = 21.18 × 10−6 K−1 is obtained. The volumetric thermal expansion coefficient is measured as αV,HT‐XRD = 43.17 × 10−6 K−1. In addition, the effectively isotropic expansion coefficients of a polycrystalline LSCF55 bar specimen are measured using a vertical high‐performance thermo‐mechanical analyzer and yield αl,bar specimen = 17.37 × 10−6 K−1 and αV,bar specimen = 52.11 × 10−6 K−1.

Widom line, dynamical crossover, and percolation transition of supercritical oxygen via molecular dynamics simulations.

Supercritical oxygen, a cryogenic fluid, is widely used as an oxidizer in jet propulsion systems and is therefore of paramount importance in gaining physical insights into processes such as transcritical and supercritical vaporization. It is well established in the scientific literature that the supercritical state is not homogeneous but, in fact, can be demarcated into regions with liquid-like and vapor-like properties, separated by the "Widom line." In this study, we identified the Widom line for oxygen, constituted by the loci of the extrema of thermodynamic response functions (heat capacity, volumetric thermal expansion coefficient, and isothermal compressibility) in the supercritical region, via atomistic molecular dynamics simulations. We found that the Widom lines derived from these response functions all coincide near the critical point until about 25 bars and 15-20 K, beyond which the isothermal compressibility line begins to deviate. We also obtained the crossover from liquid-like to vapor-like behavior of the translational diffusion coefficient, shear viscosity, and rotational relaxation time of supercritical oxygen. While the crossover of the translational diffusion coefficient and shear viscosity coincided with the Widom lines, the rotational relaxation time showed a crossover that was largely independent of the Widom line. Further, we characterized the clustering behavior and percolation transition of supercritical oxygen molecules, identified the percolation threshold based on the fractal dimension of the largest cluster and the probability of finding a cluster that spans the system in all three dimensions, and found that the locus of the percolation threshold also coincided with the isothermal compressibility Widom line. It is therefore clear that supercritical oxygen is far more complex than originally perceived and that the Widom line, dynamical crossovers, and percolation transitions serve as useful routes to better our understanding of the supercritical state.

First-principles investigation of mechanical and thermodynamic properties of nickel silicides at finite temperature -=SUP=-*-=/SUP=-

AbstractFirst-principles calculations are performed to investigate lattice parameters, elastic constants and 3D directional Young’s modulus E of nickel silicides (i.e., β-Ni_3Si, δ-Ni_2Si, θ-Ni_2Si, ε-NiSi, and θ-Ni_2Si), and thermodynamic properties, such as the Debye temperature, heat capacity, volumetric thermal expansion coefficient, at finite temperature are also explored in combination with the quasi-harmonic Debye model. The calculated results are in a good agreement with available experimental and theoretical values. The five compounds demonstrate elastic anisotropy. The dependence on the direction of stiffness is the greatest for δ-Ni_2Si and θ-Ni_2Si, when the stress is applied, while that for β-Ni_3Si is minimal. The bulk modulus B reduces with increasing temperature, implying that the resistance to volume deformation will weaken with temperature, and the capacity gradually descend for the compound sequence of β-Ni_3Si > δ-Ni_2Si > θ-Ni_2Si > ε-NiSi > θ-Ni_2Si. The temperature dependence of the Debye temperature ΘD is related to the change of lattice parameters, and ΘD gradually decreases for the compound sequence of ε-NiSi > β-Ni_3Si > δ-Ni_2Si > θ-Ni_2Si > θ-Ni_2Si. The volumetric thermal expansion coefficient αV, isochoric heat capacity and isobaric heat capacity C _ p of nickel silicides are proportional to T ^3 at low temperature, subsequently, αV and C _ p show modest linear change at high temperature, whereas C _v obeys the Dulong-Petit limit. In addition, β-Ni_3Si has the largest capability to store or release heat at high temperature. From the perspective of solid state physics, the thermodynamic properties at finite temperature can be used to guide further experimental works and design of novel nickel–silicon alloys.

Магнитообъемные эффекты в сильно коррелированных фазах плутония

AbstractThermodynamic spin fluctuations in strongly correlated plutonium (Pu) phases with exchange and spin–orbit interactions are considered. In α- and δ-Pu phases, the spin fluctuations lead to a negative magnetovolume effect that is determined by the parameter of intermode coupling and depends on features of the electron structure. It is shown that the negative volumetric thermal expansion coefficient of δ-Pu is related to an anomalously strong interaction of spin fluctuation modes.

Physical and nanomechanical properties of the synthetic anhydrous crystalline CaCO3 polymorphs: vaterite, aragonite and calcite

The synthetic anhydrous crystalline CaCO3 polymorphs—vaterite, aragonite and calcite—were tested using dilatometry and nanoindentation. Microstructural changes in the samples before and after measurements were observed under scanning electron microscope and their phase composition quantified with X-ray powder diffraction with the Rietveld method. The thermal expansion coefficients of vaterite and the hardness and elastic modulus of synthetic aragonite are reported for the first time. The physical and nanomechanical properties were measured under similar conditions for each CaCO3 polymorph. Aragonite, calcite and vaterite showed volumetric thermal expansion coefficient at 303 K of 49.2(8), 48.6(2) and 44.1(3) 10−6 K−1, respectively. The elastic modulus increased from 5(4), 16(7) to 31(8) GPa for aragonite, calcite and vaterite, respectively. Average hardness was found lower than values from the literature, ranging from 0.3 to 1.3 GPa. The results are considered of interest for the design of CaCO3-based materials for applications.

Mechanical activation effect on structure, physicochemical, and biological properties of potassium/magnesium orotates

In the present paper, the possibility of the formation of the tautomeric structure of potassium orotate and magnesium orotate in the solid state is discussed. Using ball milling, we have received the orotate samples with the predominant content of hydroxy and dihydroxy forms. The crystalline and tautomeric structures have been analyzed by XRD, IR, NEXAFS and XPS spectroscopy. There is a slight difference in the water solubility of the orotate tautomers, but the physicochemical properties (viscosity and volumetric thermal expansion coefficients) of tautomers’ water solutions significantly differ. The above differences are related to variation of hydration area of orotate anions due to the composition of the functional groups being changed together with the structure of tautomers. The residual differences in the tautomeric structure of solid orotates formed during the milling process are observed in the orotate water solutions for 1.5-2.5 hours. The biological activity of the water solution of a hydroxy form relative to erythrocytes and epithelial cells is higher than that of oxo- and dihydroxy-form water solutions.

A numerical investigation of transient natural convective heat transfer to isobutane in the supercritical region

Current research article investigates numerically the time-dependent laminar free convective supercritical fluid (SCF) flow past a vertical cylinder. Two new thermodynamic models for the SCF have been considered. Based on these proposed models, in SCF two new equations for thermal expansion coefficient is obtained on the basis of Redlich-Kwong equation of state (RK-EOS) and Van der Waals equation of state (VW-EOS). It is shown that the thermal expansion coefficient is a function of temperature, pressure and compressibility factor. The evaluated analytical values of volumetric thermal expansion coefficient using RK-EOS are closer to the experimental values which confirm the greater accuracy of proposed RK-EOS as compared to that of VW-EOS. The set of non-dimensional partial differential equations for the SCF flow over a vertical cylinder are obtained and they are time-dependent, highly non-linear and coupled. Therefore, these complex equations are solved using the computational techniques such as Crank-Nicolson implicit finite difference scheme. Numerical simulations are performed for a well-known chemical compound like isobutane in the region of its critical point. The results concerning the velocity, temperature, and average momentum and heat transport coefficient profiles across the boundary layer are shown graphically and discussed for various values of control parameters. From the obtained graphical data, it is clear that temperature plays a prominent role than the pressure under supercritical condition.

X-ray diffraction study of the caged magnetic compound DyFe [formula omitted] Zn [formula omitted] at low temperatures

We have carried out high-angle X-ray powder diffraction measurements of the caged magnetic compound DyFe2Zn20 at low temperature between 14 and 300K. Even though a strong magnetic anisotropy exists in the magnetization and magnetic susceptibility due to strong exchange interaction between Fe and Dy, almost all X-ray powder diffraction peaks correspond to Bragg reflections of the cubic structural models not only at room temperature paramagnetic state but also at low temperature magnetic ordering state. The Debye temperature is obtained to be 227K from the results of the volumetric thermal expansion coefficient, which is approximately coincident with that of CeRu2Zn20 (245K) and that of pure Zn metal (235K).

High-pressure phase transition and thermodynamic properties from first-principles calculations: Application to cubic copper iodide

The pressure-induced B3-B1 structural phase transition and some interesting thermodynamic properties for high-pressure B1 structure of cubic copper iodide (CuI) have been studied systematically using first-principles calculations based on density functional theory. It is found that CuI has a B3 ground-state phase at zero pressure and the transition pressure from B3 to B1 structure determined by the relative enthalpy versus pressure curves is about 6.9 GPa with a volume contraction of 14.42%. As a high-pressure phase, the B1 structure will be mechanically stable up to 57 GPa according to the generalized elastic stability criteria. Through the quasi-harmonic Debye model, the dependences of the primitive cell volume, isothermal bulk modulus, volumetric thermal expansion coefficient, heat capacity, entropy, and Debye temperature of CuI with high-pressure B1 phase on pressure and temperature are successfully predicted. The thermodynamic properties are summarized in the pressure range of 0–50 GPa and the temperature up to 800 K.

Physical properties and microstructures of La $$_{1-{x}}$$ 1 - x Pr $$_{{x}}$$ x PO $$_4$$ 4 monazite-ceramics

Synthetic La $$_{1-{x}}$$ Pr $$_{{x}}$$ PO $$_4$$ monazite-type powders and ceramics with 0 $$\le$$ x $$\le$$ 1 were analysed by scanning electron microscopy, high-temperature powder X-ray diffraction, dilatometry, and plane wave ultrasound spectroscopy. Ceramics were synthesised in a two-step sintering process at 1273 and 1573 K. Final densities were up to 99.3% of the theoretical densities. Each sample shows a homogeneous distribution of grain sizes, which increase with increasing sintering temperature. Grain sizes also depend on composition, with intermediate compositions yielding the largest grains. In-situ high-temperature powder X-ray diffraction shows that the volumetric thermal expansion coefficients of the monazite powders decrease with increasing Pr content. This behavior is not observed in dilatometry measurements of the bulk samples (ceramics) because their thermal expansion mainly depends on their density. Elastic properties show the same dependence on the density.

Elastic properties and thermal expansion of lead-free halide double perovskite Cs2AgBiBr6

The elastic properties and thermal expansion behavior of lead-free halide double perovskite, Cs2AgBiBr6, were studied first with the aid of first principles calculations, which were followed by experimental characterization. The calculated full elastic constants enable the complete mapping of Young’s and shear moduli, and Poisson’s ratios of Cs2AgBiBr6 along all crystallographic orientations. Results show that significant anisotropy in them despite the fact that Cs2AgBiBr6 possesses cubic symmetry. Detailed structural analysis and a spring model were utilized to rationalize the observed anisotropy. Further, the theoretical results were validated by recourse to nanoindentation and high-pressure synchrotron powder X-ray diffraction experiments. The superior mechanical behavior of Cs2AgBiBr6 over the hybrid bromide analogues, MAPbBr3 (MA=CH3NH3+), were attributed to the higher framework stiffness of the former, which is a result of the presence of relatively stronger Ag-Br and Bi-Br bonds in it. Variable temperature single crystal X-ray diffraction reveal linear and volumetric thermal expansion coefficients to be about 20% lower than those of MAPbBr3, again suggesting its higher framework rigidity. The superior stiffness, thermal expansion behavior, moisture stability, and nontoxicity of Cs2AgBiBr6 make it a strong candidate for potential applications in optoelectronics and photovoltaics.

A Material Showing Colossal Positive and Negative Volumetric Thermal Expansion with Hysteretic Magnetic Transition

AbstractIt is an ongoing challenge to design and synthesize magnetic materials that undergo colossal thermal expansion and that possess potential applications as microscale or nanoscale actuators with magnetic functionality. A paramagnetic metallocyanate building block was used to construct a cyanide‐bridged Fe‐Co complex featuring both positive and negative colossal volumetric thermal‐expansion behavior. A detailed study revealed that metal‐to‐metal charge transfer between 180 and 240 K induced a volumetric thermal expansion coefficient of 1498 MK−1 accompanied with hysteretic spin transition. Rotation of the magnetic building blocks induced change of π⋅⋅⋅π interactions, resulting in a negative volume expansion coefficient of −489 MK−1, and another hysteretic magnetic transition between 300 and 350 K. This work presents a strategy for incorporating both colossal positive and negative volumetric thermal expansion with shape and magnetic memory effects in a material.

A Material Showing Colossal Positive and Negative Volumetric Thermal Expansion with Hysteretic Magnetic Transition.

It is an ongoing challenge to design and synthesize magnetic materials that undergo colossal thermal expansion and that possess potential applications as microscale or nanoscale actuators with magnetic functionality. A paramagnetic metallocyanate building block was used to construct a cyanide-bridged Fe-Co complex featuring both positive and negative colossal volumetric thermal-expansion behavior. A detailed study revealed that metal-to-metal charge transfer between 180 and 240 K induced a volumetric thermal expansion coefficient of 1498 MK-1 accompanied with hysteretic spin transition. Rotation of the magnetic building blocks induced change of π⋅⋅⋅π interactions, resulting in a negative volume expansion coefficient of -489 MK-1 , and another hysteretic magnetic transition between 300 and 350 K. This work presents a strategy for incorporating both colossal positive and negative volumetric thermal expansion with shape and magnetic memory effects in a material.

Structure and phase transition in BaThO3: A combined neutron and synchrotron X-ray diffraction study

The structure of BaThO3, obtained by solid state synthesis, was refined for the first time by the Rietveld method using a combination of synchrotron X-ray and neutron powder diffraction data. BaThO3 has an orthorhombic structure at room temperature, in space group Pbnm with a = 6.3491(5), b = 6.3796(4) and c = 8.9907(7) Å. Heating BaThO3 to above 700 °C results in a continuous transition to a second orthorhombic structure, in space group Ibmm, demonstrated by both in situ neutron and synchrotron X-ray powder diffraction measurements. The coefficient of volumetric thermal expansion for BaThO3 is determined to be 1.04 × 10−5 °C-1 from 50 to 625 °C (Pbnm phase), and 9.43 × 10−6 °C-1 from 800 to 1000 °C (Ibmm phase). BaThO3 was found to decompose upon exposure to atmospheric moisture resulting in the formation of ThO2. The thermal expansion of ThO2, which invariably co-exists with BaThO3, is also described.

Volumetric thermal expansion coefficients of the equiatomic Na–K and K–Rb melts

The volumetric thermal expansion coefficients of the equiatomic Na–K and K–Rb melts at 373 K are calculated using variational method with an additive hard-sphere reference system. It is found that the Krasko–Gurskii model pseudopotential with the exchange-correlation Geldart–Vosko function yields better agreement with the experimental data as compared to the local Animalu–Heine pseudopotential with the exchange-correlation Toigo–Woodruff function.

Electronic structure and magnetic phase transition in MnSi

Temperature variations of the amplitude of zero-point and thermal spin fluctuations in a helicoidal ferromagnetic (MnSi) are characterized using the electronic structure model that follows from ab initio LDA + U + SO calculations. It is found that a drastic reduction in the amplitude of zero-point spin fluctuations at temperature T S (in the vicinity of the magnetic phase transition) leads to ferromagnetic solution instability (a change in the sign of the intermode interaction parameter). The observed magnetovolume effect and a sharp change in the radius of spin correlations have the same underlying cause. The results of calculation of the volumetric coefficient of thermal expansion agree well with the observed anomaly in the region of the magnetic phase transition.