Dependence Of Heat Capacity Research Articles

Dependence of Electrical and Thermal Properties on Applied Electric Field in La Doped Barium Titanate Displacive Ferroelectric Perovskites

The high dielectric constant and low dielectric loss are the most desirable characteristics of the dielectric materials. Considering the hazardous nature of lead-based ceramics, many research groups have paid great attention to the research on non-lead-based perovskites. The effect of the electric field on the electrical and thermal properties of the Lanthanum doped barium Titanate, one of the main important members of the ferroelectric Perovskites family is studied using the method of double time thermal Green’s function and Kubo formalism. With the help of the Silverman-Joseph Hamiltonian a general expression is derived. The electric field and temperature dependent dielectric constant and specific heat capacity of Ba1-xLaxTiO3 crystal has been investigated. The dielectric constant decreases with increase in temperature and applied electric field component. The variation shows a consequence of the gradual decrease in the Curie temperature of the doped material with the increase in defect concentrations. The results also compared with some previous studies done by the author and other workers on similar other materials.

Ultra-deep optical cooling of coupled nuclear spin-spin and quadrupole reservoirs in a GaAs/(Al,Ga)As quantum well

The physics of interacting nuclear spins in solids is well interpreted within the nuclear spin temperature concept. A common approach to cooling the nuclear spin system is adiabatic demagnetization of the initial, optically created, nuclear spin polarization. Here, the selective cooling of 75As spins by optical pumping followed by adiabatic demagnetization in the rotating frame is realized in a nominally undoped GaAs/(Al,Ga)As quantum well. The lowest nuclear spin temperature achieved is 0.54 μK. The rotation of 6 kG strong Overhauser field at the 75As Larmor frequency of 5.5 MHz is evidenced by the dynamic Hanle effect. Despite the presence of the quadrupole induced nuclear spin splitting, it is shown that the rotating 75As magnetization is uniquely determined by the spin temperature of coupled spin-spin and quadrupole reservoirs. The dependence of heat capacity of these reservoirs on the external magnetic field direction with respect to crystal and structure axes is investigated.

Density and heat capacity of some molten mixtures in system LiF-BeF2-UF4

The density of molten mixtures of lithium, beryllium and uranium fluorides was studied by Archimedean method. The densities of mixtures without UF4 are of close values, uranium fluoride increases density. Heat capacity was measured by DSC method. There is some difference between results obtained in cooling and heating modes due to presence of peritectic compound Li2BeF4 which manifests overcooling behavior. The dependence of specific and molar heat capacity on composition was drawn for LiF-BeF2 system. The thermal expansion values were calculated from density results. Correlation was found between heat capacity and thermal expansion of melts studied.

Thermodynamic properties of sodium hexatitanate (Na2Ti6O13) at high temperature (298.15–1573 K)

Sodium hexatitanate (Na2Ti6O13) was reported as an anode side material for Sodium ion batteries owing to low material cost, high energy efficiency, good thermal stability and long cycle life. Therefore, studies pertaining to the thermodynamic properties of Na2Ti6O13 are indispensable for improving its service performance. However, a significant number of literature reviews concerning thermodynamic properties indicated that heat capacity of Na2Ti6O13 at high temperatures should be confirmed. In this study, the 99.5% purity of Na2Ti6O13 sample was successfully prepared via solid-state reaction using TiO2 and Na2CO3 as initial materials. Heat capacity of the as-synthesized samples in the temperature range of 573–1523 K was measured using a multi-high temperature calorimeter 96 line. Heat capacity, Cp, from 298.15 to 1573 K was modeled as a polynomial formula with a prediction error of 3%: Cp = 474.08143 + 0.06286T-8.04068 × 106 T−2 (J⋅mol−1⋅K−1). In combination with the low-temperature data, heat capacity of Na2Ti6O13 from 0 to 1573 K was given in present study. Values of changes in enthalpy, Gibbs free energy and entropy in the temperature range of 298.15–1573 K were calculated based on the temperature dependence of heat capacity.

Structure and properties of (Ta1-хZrх)C and (Ta1-хHfх)C solid solutions produced by SHS and hot pressing

Self-propagating high-temperature synthesis (SHS) from elements in combination with high-energy ball milling of the reaction mixture enabled the production of powdered (Ta1-хZrх)C and (Ta1-хHfх)C solid solutions with various stoichiometry and average particle size d50 = 9 μm. Hot pressing (HP) was used for powders consolidation. All samples were found to be single-phase ones with lattice parameters following a linear function of the solid solution composition. The resulting dense samples of (Ta1-хZrх)C and (Ta1-хHfх)C solid solutions showed a notable growth of hardness and Young's modulus in comparison with ТаС carbide. The solid solution strengthening effect involving increase mechanical properties with growing content of Zr and Hf was confirmed. Temperature dependence of heat capacity, thermal diffusivity, thermal conductivity, and electric resistance was measured. Both Zr-and Hf-doped carbides showed high resistance to plasma torch impact at a temperature up to 3000°С. The high resistance towards ultra-high-temperature oxidation and erosion is provided by as-forming oxycarbide layers with high adhesion to the carbide matrix.

Synthesis, characterization and thermodynamic properties of KNbO3

The potassium niobate (KNbO3) sample was hydrothermally synthesized using Nb2O5 and KOH solution as precursors. X-ray diffraction (XRD) results show that the synthesized KNbO3 is a single-phase material with an orthorhombic crystal structure and the unit cell parameters are: a = 3.9743 (2) Å; b = 5.6954 (2) Å; c = 5.7229 (2) Å; α = β = γ = 90°, V = 129.54 (1) Å3. The temperature-dependent phase transitions and enthalpy changes of KNbO3 were investigated by Differential Scanning Calorimetry (DSC) method. The heat capacity was measured experimentally by relaxation time method via physical property measurement system (PPMS, 2–300 K) and DSC sapphire method (280–820 K), respectively. The heat capacity of KNbO3 (2–300 K) was piecewise fitted into polynomials as: Cp = 3.242 × 10−1 T + 1.540 × 10−3 T3 + 1.056 × 10−4 T5-1.098 × 10−6 T7 + 2.946 × 10−9 T9 (2–10 K), Cp = 3.275 + 0.005 T + 0.044 T2-6.816 × 10−4 T3 + 4.628 × 10−5 T4-1.343 × 10−6 T5 + 1.090 × 10−8 T6 (10–50 K), Cp = 88.211 + 69.280 × 10−3 T-0.580 × 105 T−2-8.685 × 105 T2 (50–300 K). Consequently, the changes of enthalpy, entropy, Gibbs free energy and equilibrium constant were calculated based the dependence of heat capacity and temperature (280–820 K).

Layered ceramics based on InGaO3(ZnO)2: Preparation and experimental investigation of high-temperature heat capacity and thermal conductivity

This paper reports on a method for producing ceramics from a high-purity, submicron InGaO3(ZnO)2 powder synthesised using a PVA-assisted gel combustion method, as well as an experimental study of the thermophysical properties of the ceramic materials obtained. The platelet-like crystallites of the InGaO3(ZnO)2 obtained were several microns long and up to several hundred nanometres thick. Layered ceramics obtained by sintering compacted InGaO3(ZnO)2 powders at temperatures of 1373–1773 K had a bulk density that was 68–96 % of the theoretical density. The temperature dependence of heat capacity in the range 306–1346 K was studied experimentally for InGaO3(ZnO)2 using the DSC method. It was found that, in the range 323–1173 K, layered InGaO3(ZnO)2 ceramics had a low thermal conductivity, which decreased from 2.0–1.3 W/(m K. The results obtained make it possible to consider this material as a promising thermal barrier coating.

Thermodynamic properties of sodium trititanate (Na2Ti3O7) at high temperature (298.15‐1403 K)

AbstractSodium‐ion batteries (NaIBs) have attracted extraordinary attentions as a promising scalable energy storage alternative to current lithium‐ion batteries (LIBs), owing to their natural abundance and low costs. Sodium trititanate (Na2Ti3O7) is a promising material as the material of NaIBs with low potential and high theoretical capacitance. In order to better understand their service performance when utilized in rechargeable NaIBs, studies on thermodynamic properties of Na2Ti3O7 are indispensable. However, an extensive literature review revealed that the heat capacity of Na2Ti3O7 is established with divergences, especially for high‐temperature region. Therefore, the 99.5% purity of Na2Ti3O7 powder was first Synthesized through solid‐state reaction with sodium carbonate (Na2CO3) and titanium dioxide (TiO2) as raw materials. The as‐prepared samples were used to measure the heat capacity from 573 to 1323 K which was carried out with multihigh temperature calorimeter (MHTC) 96 line. The temperature dependence of heat capacity was modeled as a function: Cp =255.51073 + 0.06059 T − 3.86912 × 106 T−2 (J mol−1 K−1) (298.15 ‐ 1403 K), and then used for computing changes in enthalpy, entropy, and Gibbs free energy. Heat capacity of Na2Ti3O7 from 0 to 1403 K was given for future application of Na2Ti3O7 in rechargeable batteries.

Structural, magnetic and thermodynamic properties of barium ferromolybdate

ABSTRACT The heat capacity and magnetisation of the obtained by the solid-phase method from simple oxides single-phase compound Ba2FeMoO6-δ, in which the superstructural ordering of Fe and Mo cations occurs, was studied. The anomalous behaviour of the temperature dependences of heat capacity (deviation from Debye T 3 law) and magnetic moment (ZFC mode) is interpreted as the existence of a superparamagnetic state in nanoscale grains. The second λ-type anomaly of heat capacity in the region of 300 K is due to the transition of the compound from the ferrimagnetic to the paramagnetic state. The Curie temperature, determined from the maximum of excess heat capacity in the region, is in good agreement with the Curie temperature obtained from the results of magnetic measurements, TC = 302 K. Based on the Ba2FeMoO6-δ compounds heat capacity data the next thermodynamic functions were calculated: reduced enthalpy, entropy, reduced Gibbs energy. The values of calculated functions in the region of temperature anomalies made it possible to classify such anomalies as second-order phase transitions.

Temperature dependent crystal structure re‐determination and electronic properties of UI3

AbstractIn this work, we have re‐investigated the structural and physical properties of UI3 by means of temperature dependent powder neutron diffraction, heat capacity and magnetic measurements. We confirm that UI3 crystallizes in the PuBr3 structure type, space group Cmcm. We did not observe any temperature dependent structural phase transition in the temperature range from 10 to 300 K. We further report the first quantum chemical calculations of UI3 by density functional theory (DFT). The calculated structural and electronic properties demonstrate the pronounced two‐dimensional anisotropic effects present in UI3 due to its layered structure.

Magnetic phase transition and lattice dynamic features in ErB2C borocarbide

A sample of erbium borocarbide ErB2C was synthesized from a stoichiometric mixture of erbium, boron, and pyrographite hydride. Temperature dependent magnetic susceptibility, heat capacity and lattice parameters of borocarbide at 2–300 K were experimentally investigated, the Raman spectrum was determined and analyzed. Sharp anomalies in the heat capacity and magnetic properties of ErB2C near T = 16.3 K, caused by the transition to the antiferromagnetic state, as well as diffuse anomalies at a higher temperature, caused by the effect of the crystal field (Schottky anomalies) were revealed. It was found that the magnetic phase transition does not cause measurable anomalies in the lattice parameters of borocarbide due to the weak coupling between the Er3+ ion subsystem and the B–C layers. Almost zero thermal expansion of erbium borocarbide in the basal plane (along a and b axes) (anisotropic invar effect) as well as an unusual character of the c-axis thermal expansion were observed. The first of these features is due to the high bonding energy in the B–C layers and the weak bond between the layers in the borocarbide crystal lattice. It was found that the anomalous expansion along the c axis is a consequence of the action of the crystal field. The splitting scheme for the ground level of Er3+ ions by crystal field was determined from the analysis of the Schottky anomaly of the heat capacity.

Thermal Weakening Friction During Seismic Slip: Experiments and Models With Heat Sources and Sinks

AbstractExperiments that systematically explore rock friction under crustal earthquake conditions reveal that faults undergo abrupt dynamic weakening. Processes related to heating and weakening of fault surfaces have been invoked to explain pronounced velocity weakening. Both contact asperity temperature Ta and background temperature T of the slip zone evolve significantly during high‐velocity slip due to heat sources (frictional work), heat sinks (e.g., latent heat of decomposition processes), and diffusion. Using carefully calibrated High‐Velocity Rotary Friction experiments, we test the compatibility of thermal weakening models: (1) a model of friction based only on T in an extremely simplified, Arrhenius‐like thermal dependence; (2) a flash heating model which accounts for the evolution of both V and T; (3) same but including heat sinks in the thermal balance; and (4) same but including the thermal dependence of diffusivity and heat capacity. All models reflect the experimental results but model (1) results in unrealistically low temperatures and model (2) reproduces the restrengthening phase only by modifying the parameters for each experimental condition. The presence of dissipative heat sinks in stage (3) significantly affects T and reflects on the friction, allowing a better joint fit of the initial weakening and final strength recovery across a range of experiments. Temperature is significantly altered by thermal dependence of (4). However, similar results can be obtained by (3) and (4) by adjusting the energy sinks. To compute temperature in this type of problem, we compare the efficiency of three different numerical approximations (finite difference, wavenumber summation, and discrete integral).

Time fractional heat transfer analysis in thermally sensitive functionally graded thick hollow cylinder with internal heat source and its thermal stresses

The aim of this work is to investigate the time fractional thermoelastic state of a thermally sensitive functionally graded thick hollow cylinder subjected to internal heat source. Convection boundary conditions are applied on the curved surface of cylinder also sectional heating is assumed on the lower surface. The material properties except density and Poisson’s ratio are assumed to be dependent on temperature. Kirchhoff’s variable transformation is used to reduce the nonlinear heat conduction with temperature dependent thermal conductivity and specific heat capacity to linear form. Further the solution of linear form is obtained by using integral transform technique in the form of Bessel’s and trigonometric functions. All physical and mechanical quantities are taken as dimensional for the theoretical analysis whereas for numerical computations non-dimensional parameters are assumed. Numerical results of temperature change and stress distribution are illustrated graphically for ceramic-metal-based functionally graded materials and shown in figures with the help of Mathematica software.

THERMAL PHYSICAL ASPECTS OF DETERMINATION OF LOAD CAPACITY MEDIUM VOLTAGE POWER CABLES WITH CROSS-POLYETHYLENE INSULATION IN STATIONARY OPERATING MODES

Currently, the development trends of global medium voltage cable networks are aimed at the introduction of cables with cross-linked polyethylene insulation. Such cables have a higher operating temperature, which allows to increase their throughput, and increased stability when working in conditions of overload and short circuits. It is possible to determine the allowable heat and electrical loads only if the heat balance is observed. Fundamentally important for solving the problems of heat balance is the significant dependence of thermal conductivity and heat capacity of polyethylene insulation on temperature. It is established that the capacity of the cable, determined by regulatory models and average environmental parameters, provides only preliminary information about its heating. For certain requirements and for innovative cable designs, a necessary condition for determining the load capacity in real stationary modes of operation is the use of the heat balance model. A system of mathematical equations is proposed, which due to the combination of structural and thermophysical parameters of the cable with the conditions of the external environment allows to determine the parameters of the stationary thermal regime of the cable at any load current.

Thermodynamics of caesium niobium molybdenum oxide CsNbMoO6

Firstly in the present research, the heat capacity Cp,mo = f(T) of crystalline caesium niobium molybdenum oxide CsNbMoO6 was measured in the range of T = (6 and 340) K by the precise adiabatic vacuum calorimeter. The phase purity and composition homogeneity of prepared sample have been confirmed by X-ray diffraction analysis and X-ray microanalysis. The standard thermodynamic functions (p° = 0.1 MPa) of CsNbMoO6, namely Cp,mo, Δ0THmo, Δ0TSmo and Δ0TGmo, were calculated using the obtained experimental data from T → 0 to 340 K. The low-temperature (T < 50 K) heat capacity dependence was analyzed on the basis of the Debye heat capacity theory of solids and its multifractal model, so the characteristic temperature and the fractal dimension were determined, and chain-layered structure topology of the studied compound was established. The standard thermodynamic functions of crystalline CsNbMoO6 formation at T = 298.15 K were calculated.

New insights into temperature-dependent ice properties and their effect on ice shell convection for icy ocean worlds

Ice shell dynamics are a critical control on the habitability of icy ocean worlds. Here, we present a systematic study evaluating the effect of temperature-dependent material properties on these dynamics. We review the published thermal conductivity data for ice, which demonstrates that the most commonly used conductivity model in planetary science represents a lower bound. We propose a new model for thermal conductivity that spans the temperature range relevant to the ice shells of ocean worlds. This increases the thermal conductivity at low temperatures near the surface by about a fifth. We show that such an increase in thermal conductivity near the cold surface favors conduction over convection in the ice shell of Europa. Furthermore, we find that including temperature dependent specific heat capacity decreases the energy stored in the conductive lid. Thus, the timescale for ice shell response to thermal perturbations is reduced by approximately one third. An ice shell that is more sensitive to thermal perturbations may help to explain surface features such as chaotic terrains which require large additions of energy to the near-surface ice.

Calorimetric Study of Ionic Liquids Based on 4-Vinylbenzyl Triethylammonium with Chloride and Tetrafluoroborate Anion

In the present research, the temperature dependence of heat capacity of two ionic liquids VBTEA-Cl (1) and VBTEA-BF4 (2) were studied. 4-Vinylbenzyl triethylammonium chloride was synthesized by original methodic. 4-Vinylbenzyl triethylammonium tetrafluoroborate was obtained via anion exchange reaction. Compounds was characterized by FTIR and NMR spectroscopies, their purity was proven. Compounds 1 and 2 were studied by different scanning calorimetry over the temperature range from 300 to 600 K. The melting point were determined for both substances, but 4-vinylbenzyl pyridine triethylammonium tetrafluoroborate wasn’t stable after melting in contrast with 4-vinylbenzyl pyridine chloride. The experimental data were used to calculate the enthalpy of phase transition (melting) for compound 1.

Calorimetric Study of Ionic Liquids Based on 4-Vinylbenzyl Triethylammonium with Chloride and Tetrafluoroborate Anion

In the present research, the temperature dependence of heat capacity of two ionic liquids VBTEA-Cl (1) and VBTEA-BF4 (2) were studied. 4-Vinylbenzyl triethylammonium chloride was synthesized by original methodic. 4-Vinylbenzyl triethylammonium tetrafluoroborate was obtained via anion exchange reaction. Compounds was characterized by FTIR and NMR spectroscopies, their purity was proven. Compounds 1 and 2 were studied by different scanning calorimetry over the temperature range from 300 to 600 K. The melting point were determined for both substances, but 4-vinylbenzyl pyridine triethylammonium tetrafluoroborate wasn’t stable after melting in contrast with 4-vinylbenzyl pyridine chloride. The experimental data were used to calculate the enthalpy of phase transition (melting) for compound 1.

Symmetry change of d -wave superconductivity in κ -type organic superconductors

Magnetic-field-angle-resolved heat capacity of dimer-Mott organic superconductors $\kappa$-(BEDT-TTF)$_2$$X$ is reported. Temperature and field dependence of heat capacity indicates that the superconductivity has line nodes on the Fermi surface, which is a typical feature of $d$-wave superconductivity. In-plane field-angle dependence exhibits fourfold oscillations as well as twofold oscillations due to anisotropy of superconducting gap functions. From analyses of the fourfold term, the gap symmetry is determined as $d_{x^{2}-y^{2}}$+$s_{\pm}$ for $X$=Cu[N(CN)$_2$]Br and $d_{xy}$ for $X$=Ag(CN)$_2$H$_2$O. We suggest that the symmetry difference comes from the competition of $d_{xy}$ and $d_{x^{2}-y^{2}}$ antiferromagnetic fluctuations depending on lattice geometry.

Numerical analysis of static and dynamic heat transfer behaviors inside proton exchange membrane fuel cell

One dimension, two-phase transient proton exchange membrane fuel cell (PEMFC) thermal models, accounting for most relevant heat sources and energy transport terms, are presented. These thermal models fully consider the thermal contact resistance between gas diffusion backing (GDB) and bipolar plate, and the dependence of thermal conductivity (TC) and specific heat capacity (SHC) on liquid water, enabling the study of static and dynamic heat transfer behaviors under current loads and water conditions. In this paper, we first discussed current loads on temperature distribution, maximum temperature, transient response, and other thermal characters within the fuel cell. A noticeable temperature jump inside the cathode catalyst layer (CCL) is observed as the current step changes, induced by the different transients of heat generation and energy transport. Subsequently, the effects of water conditions are investigated. It is found that the liquid water dramatically affects the distribution and variation of temperature due to its high TC and SHC. Lastly, sensitivity analysis reveals that the TC of dry GDB contributes much to CCL's high temperature, which indicates that improving GDB TC is very important to avoid CCL overheating and explains the lower temperature gradient inside PEMFC under relatively wet conditions.