Temperature Dependence Of Heat Capacity Research Articles

Thermodynamic properties of MnV2O6 and Mn2V2O7 at high temperatures

MnV2O6 and Mn2V2O7 are the key compounds during the manganese salt roasting for extracting vanadium from vanadium bearing slag. Thermodynamic properties of MnV2O6 and Mn2V2O7 are dispensable to get insight into the multi-phase reaction mechanism and clarify the phase evolution. In this study, the MnV2O6 and Mn2V2O7 compounds were synthesized through solid-state roasting routes under a nitrogen gas atmosphere, and their crystal structure and thermodynamic properties were determined using X-ray powder diffraction, differential scanning calorimetry, and drop calorimetry. The enthalpy increments of MnV2O6 and Mn2V2O7 were experimentally measured for temperatures ranging from 573 K to 1023 K and 573 K to 1173 K, respectively, using drop calorimetry for the first time. Based on the experimentally measured enthalpy increments, the temperature dependence of the molar heat capacity of MnV2O6 and Mn2V2O7 was then derived. Furthermore, thermodynamic properties such as enthalpy, entropy, and Gibbs free energy were also calculated. Finally, the Gibbs free energy of the chemical reactions during the roasting of vanadium slag was evaluated, and compared with other roasting techniques.

Characterization and Application of Cyrene as a Biomass-Based Solvent for Homogeneous Heck-Coupling Reaction.

Cyrene, a renewable, non-toxic substance having negligible vapor pressure, even at high temperatures, was proposed as a reaction medium for homogeneous Pd-catalyzed Heck-coupling reactions. It was first characterized by its temperature-dependent physicochemical properties, i.e., vapor pressure, density, surface tension, heat capacity, and viscosity, the key parameters of its reaction and process chemistry. Its refractive indices in the function of temperature were also determined. Hereafter, the effect of reaction parameters (Pd source, nature of the base, the water content of the reaction mixture, leaving group (-I, -Br, -Cl, and -OTf of aromatic substrates) on Pd-catalyzed Heck-coupling reaction was investigated using iodobenzene and styrene as model substrates. Subsequently, 4-substituted iodobenzene and styrene derivatives were applied to investigate the effect of electronic parameters on the reaction efficiency and functional group tolerance. To demonstrate the applicability of the system, thirteen stilbene derivatives were isolated with good to high yields and purity (> 95%) using 0.2 mol% of Pd, 1.5 eq. of Et3N as a base, in 1 mL of Cyrene for 2 h at 100 °C.

Фізичні властивості нанокомпозитів ПХТФЕ-ТРГ та ПХТФЕ-ТРГ/SiO2

Polymeric nanocomposites based on polychlorotrifluoroethylene (PCTFE) with a low content of dispersed thermally expanded graphite TRG and modified filler TRG/SiO2, characterized by high electrophysical properties, were obtained. The features of the electronic structure of the composite surface have been investigated. The regularities of changes in the electrophysical properties of the composites depending on the content of fillers and temperature have been established. On the basis of studies and comparative analysis of the thermophysical properties (specific heat capacity cp, temperature coefficient of linear expansion a) of the systems, the influence of the structural morphological state of the components and their concentration, the level of interfacial interaction on the physical properties of nanocomposites have been investigated.It has been established that the modified nanofiller is more active towards the polymer matrix than the unmodified one. The composites exhibit a double effect of the modified nanofiller on the matrix structure, which consists in the formation of a powerful crystal structure in the zones of influence of the nanofiller and amorphization of the polymer matrix in the peripheral zones. It has been found that the amorphization of the matrix results in a decrease in the area of temperature reflexes peaks on the temperature dependences of the specific heat capacity and a change in the absolute value of the temperature coefficient of linear expansion with an increase in the concentration of the modified TRG.

Precise integration boundary element method for solving nonlinear transient heat conduction problems with temperature dependent thermal conductivity and heat capacity

The precise integration boundary element method (PIBEM) is used to solve nonlinear transient heat conduction problems with temperature dependent thermal conductivity and heat capacity in this article. At first, a boundary-domain integral equation can be obtained by using the fundamental solution for steady linear heat conduction problems. Secondly, the domain integrals are converted into boundary integrals by using the radial integration method to get a pure boundary integral equation, which can retain the advantage of dimension reduction of the boundary element method. Then, after discretization, a first-order nonlinear differential equation system in time is obtained, and the precise integration method with predictor-corrector technique is used to solve the system of nonlinear equations. In the end, several numerical examples are presented to verify the accuracy and stability of the presented method. The results obtained by the presented method are less affected by the time step size and satisfactory results can be obtained even for a large time step size.

Large electrocaloric effect across the non-hysteretic electrostructural phase transition in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 ceramics

Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (εr) and specific heat capacity (Cp) confirmed the presence of thermal hysteresis in two phase transitions near 233 ± 10 K and 254 ± 10 K, and a non-hysteretic behavior at the Curie temperature (TC∼373 ± 10 K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature across TC. A large adiabatic temperature change of |∆T| = 0.52 K, isotropic entropy change |∆S| = 0.68 J/kg.K, electrocaloric coefficients, |∆T/∆E |= 0.311 K.mm/kV and |∆S/∆E| = 0.41 J.mm/K.kg.kV were obtained at 380 K for an electric field of 16.7 kV/cm. Obtained value of |∆T/∆E| is relatively good, reported among other BaTiO3-based ceramics.

Toward better understanding of anharmonic structural, thermodynamic, and elastic properties of CaSiO3 perovskite under extreme conditions via statistical moment method

CaSiO3 perovskite is thought to be the third most abundant minerals in both the Earth’s transition zone and lower mantle but its structural, thermodynamic, and elastic properties have not been well characterized. In this work, for the first time, we apply the statistical moment method (SMM) to determine analytical expressions of thermoelastic quantities such as isothermal and adiabatic elastic moduli, Grüneisen parameter, Young’s and shear moduli, compression wave and shear velocities including the full anharmonic effects of thermal lattice vibrations of perovskite crystals with cubic structure. The theoretical results are applied for numerical calculations for cubic CaSiO3 perovskite, which is a strongly anharmonic system, at temperatures and pressures up to 4000 K and 180 GPa corresponding to the extreme conditions of the Earth’s lower mantle. Our results for temperature and pressure dependences of unit cell volume, thermal expansivity, isochoric and isobaric heat capacities, Grüneisen parameter, isothermal and adiabatic elastic moduli, Young’s and shear moduli, compression wave and shear velocities are important signs of anharmonic effects under high temperatures and pressures. The SMM results are compared with experiments and other calculations. The present study provides an effective theoretical approach for finding the structural, thermodynamic, and elastic properties of strongly anharmonic materials under extreme conditions.

Fragility and Tendency to Crystallization for Structurally Related Compounds.

The present study was designed to investigate the physical stability of three organic materials with similar chemical structures. The examined compounds revealed completely different crystallization tendencies in their supercooled liquid states and were classified into three distinct classes based on their tendency to crystallize. (S)-4-Benzyl-2-oxazolidinone easily crystallizes during cooling from the melt; (S)-4-Benzylthiazolidine-2-thione does not crystallize during cooling from the melt, but crystallizes easily during subsequent reheating above Tg; and (S)-4-Benzyloxazolidine-2-thione does not crystallize either during cooling from the melt or during reheating. Such different tendencies to crystallize are observed despite the very similar chemical structures of the compounds, which only differ in oxide or sulfur atoms in one of their rings. We also studied the isothermal crystallization kinetics of the materials that were shown to transform into a crystalline state. Molecular dynamics and thermal properties were thoroughly investigated using broadband dielectric spectroscopy, as well as conventional and temperature-modulated differential scanning calorimetry in the wide temperature range. It was found that all three glass formers have the same dynamic fragility (m = 93), calculated directly from dielectric structural relaxation times. This result verifies that dynamic fragility is not related to the tendency to crystallize. In addition, thermodynamic fragility predictions were also made using calorimetric data. It was found that the thermodynamic fragility evaluated based on the width of the glass transition, observed in the temperature dependence of heat capacity, correlates best with the tendency to crystallize.

Cooperative Conformational Transitions Underpin the Activation Heat Capacity in the Temperature Dependence of Enzyme Catalysis.

Many enzymes display non-Arrhenius behavior with curved Arrhenius plots in the absence of denaturation. There has been significant debate about the origin of this behavior and recently the role of the activation heat capacity (ΔCP⧧) has been widely discussed. If enzyme-catalyzed reactions occur with appreciable negative values of ΔCP⧧ (arising from narrowing of the conformational space along the reaction coordinate), then curved Arrhenius plots are a consequence. To investigate these phenomena in detail, we have collected high precision temperature-rate data over a wide temperature interval for a model glycosidase enzyme MalL, and a series of mutants that change the temperature-dependence of the enzyme-catalyzed rate. We use these data to test a range of models including macromolecular rate theory (MMRT) and an equilibrium model. In addition, we have performed extensive molecular dynamics (MD) simulations to characterize the conformational landscape traversed by MalL in the enzyme-substrate complex and an enzyme-transition state complex. We have crystallized the enzyme in a transition state-like conformation in the absence of a ligand and determined an X-ray crystal structure at very high resolution (1.10 Å). We show (using simulation) that this enzyme-transition state conformation has a more restricted conformational landscape than the wildtype enzyme. We coin the term "transition state-like conformation (TLC)" to apply to this state of the enzyme. Together, these results imply a cooperative conformational transition between an enzyme-substrate conformation (ES) and a transition-state-like conformation (TLC) that precedes the chemical step. We present a two-state model as an extension of MMRT (MMRT-2S) that describes the data along with a convenient approximation with linear temperature dependence of the activation heat capacity (MMRT-1L) that can be used where fewer data points are available. Our model rationalizes disparate behavior seen for MalL and previous results for a thermophilic alcohol dehydrogenase and is consistent with a raft of data for other enzymes. Our model can be used to characterize the conformational changes required for enzyme catalysis and provides insights into the role of cooperative conformational changes in transition state stabilization that are accompanied by changes in heat capacity for the system along the reaction coordinate. TLCs are likely to be of wide importance in understanding the temperature dependence of enzyme activity and other aspects of enzyme catalysis.

High-resolution and high-accuracy calorimetry of order–disorder and melting transitions in the n-alkanes n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane and n-eicosane

In this work, a Peltier-element-based adiabatic scanning calorimeter was used to investigate, with high-resolution and accuracy, the temperature dependence of the specific heat capacity and specific enthalpy difference of a series of linear alkanes. More specifically, results are reported for the even n-alkanes; namely n-eicosane, n-octadecane, n-hexadecane and for the odd n-alkanes, namely n-nonadecane, n-heptadecane and n-pentadecane. The measurements cover a temperature range from well in the crystalline solid phase across the solid–solid transitions (when present) in to the liquid phase across the melting transition. Accurate transition temperatures and heat of transitions were derived from the direct experimental data in view of the potential use of n-alkanes as phase change materials.

Temperature Dependence of the Specific Heat Capacity Glasses Produced Based on Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> + Bi<sub>2</sub>O<sub>3</sub>

In this work, the temperature dependence of the specific heat capacity of glasses obtained on the basis of the Na2B4O7 + Bi2O3 compound with different concentrations of sodium tetraborate and bismuth oxide in the initial mixture was studied experimentally during cooling. It has been experimentally shown that with a change in the concentration of the initial substances, the specific heat capacity of the sample’s changes, and a shift of the maxima towards low temperatures is observed with an increase in the concentration of bismuth oxide. A physical interpretation of the nature of the maximum on the temperature dependence of the specific heat is given.

Influence of lithium on the temperature dependence of heat capacity and thermodynamic functions changes in AK1 alloy based on high-purity aluminum

The heat capacity of the AK1 alloy based on high-purity aluminum with lithium was determined in the cooling mode using the known heat capacity of the reference aluminum sample. By means of mathematical processing of cooling rate curves of samples from AK1 alloy with lithium and the reference sample, polynomials describing their cooling rates were obtained. Further, the polynomials of the temperature dependence of the heat capacity of alloys, described by a four-member equation, were established using the experimentally found values of the cooling rates of samples from alloys and the standard, taking into account their mass. Using integrals from specific heat capacity, models of temperature dependence of enthalpy, entropy and Gibbs energy changes were established. It was found that the heat capacity of the alloys increases with rising temperature. The addition of lithium when the temperature is up to 600 K significantly increases the heat capacity, and at temperatures above 600 K lithium in amounts of 0.5 wt. % reduces the heat capacity of the initial alloy AK1. It is shown that lithium addition increases the enthalpy and entropy of the initial AK1 alloy and decreases the Gibbs energy value.

The implications of a temperature-dependent heat capacity DCp(t) on temperature-dependent gating in thermoTRPs

The implications of a temperature-dependent heat capacity DCp(t) on temperature-dependent gating in thermoTRPs

Thermophysical properties of the biofuel components: A mini-guide to the critical properties, heat capacities, and thermal conductivities

Experimental data on the critical temperature, critical pressure, heat capacity, and thermal conductivity of the compounds involved in the production of biofuels have been compiled and critically evaluated. The compilation contains the critical temperature and critical pressure of 56 compounds, the heat capacity of 63 compounds, and the thermal conductivity of 35 compounds and covers the period from 1886 to September 2023. The recommended values of the critical temperatures and pressures have been determined. The parameters of correlating polynomials for the temperature dependence of heat capacities and thermal conductivities have been obtained. The compounds under consideration are the components of biofuels or platform chemicals. Some methyl and ethyl esters of saturated and unsaturated acids, furanic compounds, levulinic acid and alkyl levulinates, gamma-valerolactone, alpha-angelica lactone, triglycerides, and several alkyl pentanoates are among the compounds studied.

Heat Capacity of Indium or Gallium Sesqui-Chalcogenides.

The chalcogenides of p-block elements constitute a significant category of materials with substantial potential for advancing the field of electronic and optoelectronic devices. This is attributed to their exceptional characteristics, including elevated carrier mobility and the ability to fine-tune band gaps through solid solution formation. These compounds exhibit diverse structures, encompassing both three-dimensional and two-dimensional configurations, the latter exemplified by the compound In2Se3. Sesqui-chalcogenides were synthesized through the direct reaction of highly pure elements within a quartz ampoule. Their single-phase composition was confirmed using X-ray diffraction, and the morphology and chemical composition were characterized using scanning electron microscopy. The compositions of all six materials were also confirmed using X-ray photoelectron spectroscopy and Raman spectroscopy. This investigation delves into the thermodynamic properties of indium and gallium sesqui-chalcogenides. It involves low-temperature heat capacity measurements to evaluate standard entropies and Tian-Calvet calorimetry to elucidate the temperature dependence of heat capacity beyond the reference temperature of 298.15 K, as well as the enthalpy of formation assessed from DFT calculations.

A theoretical study of Lifshitz transition for 2H-TaS2.

Lifshitz transition was proposed to explain a change of the topology structure in a Fermi surface induced by continuous lattice deformation without symmetry breaking since 1960. It is well known that the anomalies of the kinetic coefficients (the coefficient of heat conduction and electrical conductivity, viscosity, sound absorption, etc.) are usually closely connected with the Lifshitz transition behavior. 2H-TaS2 is a typical representative to study its anomalies of temperature dependence of heat capacity, resistivity, Hall effect, and magnetic susceptibility. Its geometrical structure of the charge density wave (CDW) phase and layer number dependence of carrier-sign alternation upon cooling in the Hall measurements have not been well understood. The geometrical structure (T-Ts) of the CDW phase was predicted through first principles calculations for bulk and mono-layer 2H-TaS2. Driven by electron-lattice coupling, Ta atoms contract to form a partially gapped CDW phase. The CDW phase has a larger average interlayer separation of S-S atoms in the adjacent two layers compared with the metal phase, which results in a weaker chemical bonding among S-S atoms in the adjacent two layers and then a narrower bandwidth of the energy band. The narrower bandwidth of the energy band leads to a larger density of states (DOS) in the out-of-plane direction above the Fermi level for the CDW phase. As the Fermi level continually drops from the DOS region with a negative slope to that with a positive slope on cooling, the reversal of the p → n type carrier and the pocket-vanishing-type Lifshitz transition occur in the bulk 2H-TaS2. However, the Fermi level slightly drops by 6 meV and happens to be at the positions of pseudo band gaps, so the reduction of in-plane DOS and total DOS is responsible for the always p-type carrier in the mono-layer samples. Our CDW vector of the k-space separation between two saddle points is QSP ≈ 0.62 GK and can provide a theoretical support for the "saddle-point" CDW mechanism proposed by Rice and Scott. Our theoretical explanation gives a new understanding of both Lifshitz transition for symmetry breaking and reversal for the p-n carrier sign in the Hall measurements in various two-dimensional transition metal disulfides.

In English

The article discusses the use of KDP ferroelectric crystals (phosphates and arsenates of potassium, rubidium, cesium) and their deuterated analogues in various industries, including the creation of electro-optical devices and as hydrogen sorbents. The paper describes the physical properties of KDP crystals, changes in their properties near the phase transition temperature, as well as methods for obtaining KDP nanocrystals and their application in biomedicine. The paper also states that the phase transition in KDP crystals occurs near room temperature and manifests itself in a change in their physical properties, such as dielectric constant, optical properties, and heat capacity. In addition, approaching the phase transition temperature causes a change in the crystal lattice parameters, which can lead to the appearance of anomalous effects. The structure of the unit cell of potassium dihydrogen phosphate (KH2PO4) is considered. The plots of the temperature dependence of the order parameter of spontaneous polarization and the plots of the temperature dependence of the configurational heat capacity of the crystal in the phase transition region are calculated, and the plots of the temperature of the inverse and direct dielectric susceptibility are calculated. Graphs of the order parameter, which characterizes the degree of spontaneous polarization for different temperatures, depending on the strength of the external electric field, are also calculated.

Complete thermodynamic characterization of second-order phase transition magnetocaloric materials exclusively through magnetometry

To fully assess and improve the performance of near room-temperature magnetic refrigerants, it is crucial to measure and compare their three most relevant thermodynamic properties, and their dependence on temperature (T) and applied magnetic field (H): the isothermal entropy change, ∆Siso(T,H); the adiabatic temperature change, ∆Tad(T,H); and the heat capacity, Cp(T,H). Typically, each thermodynamic property requires its own specialized measurements, which are very time-demanding and can be challenging to setup. In this work, we report a complete thermomagnetic characterization of a benchmark magnetocaloric material, gadolinium, using a single and commercially available SQUID magnetometer. By improving a recently reported method with incremental field ramping steps for measuring temperature through magnetization, we obtained a ∆Tad(T) curve under a 1 T field change with its peak amplitude and maximizing temperature respectively within 2 % and 0.8 % of previously reported values for gadolinium. We were also able to estimate the temperature dependent heat capacity, Cp(T,μ0H=0.85T), using the ∆Tad(T) measurements from magnetometry combined with magnetization versus temperature curves at different field values. This estimate of Cp around the transition temperature of gadolinium is within a relative error of 11 % of the experimental and reported values. The reported methodology allows the complete characterization of a second-order magnetocaloric material (∆Siso(T,H), ∆Tad(T,H), Cp(T,H)) around its Curie temperature using a single and widely available device, which can accelerate studies of different magnetocaloric materials’ performance, and approximate their implementation in magnetic refrigeration and/or waste heat energy harvesting industries.

Detailed Approach to Calculate the Heat Generation of Lithium-Ion Cells during Heat-Wait-Seek Tests in Accelerating Rate Calorimetry

By means of the Heat-Wait-Seek test in Accelerating Rate Calorimeters (ARC) the safety performance of Lithium-ion cells can be estimated. The most interesting measured parameters that can be extracted from these tests are the critical temperatures, such as the onset of self-heating, the venting or thermal runaway temperature. Another essential safety factor is the generated heat during cell failure. In general, the generated heat is calculated by an average heat capacity of the cell and the temperature difference in the experiment, which is not accurate enough especially when facing the challenges in specific volumetric energy density and safety of battery packs.In this study a more accurate way to calculate the generated heat is proposed, which consists of using temperature dependent heat capacity of the cell, based on its individual components. This leads to a significant difference in the calculated generated heat, for instance the specific heat capacity of NMC as a cathode material increases in the temperature range from 298 K to 398 K from 0.83 to 0.96 J/g·K, which is an increase of about 16 %. This leads to a difference in the calculated generated heat in this small range of 7 J/g (or 8 %), if a static specific heat capacity of 0.83 J/g·K and on the other hand a temperature dependent specific heat capacity is used. Moreover, the influence of additional heating steps, venting of the cell, melting of the separator and the overall accuracy of the measurement will be discussed. The investigation of these effects is in the focus of the project AnaLiBa (Analytics of Lithium-ion-Batteries), funded by the German Federal Ministry of Education and Research (BMBF) in the framework of the competence cluster Analytics/quality assurance (AQua). In this project the approach is applied to commercial type 21700 cells. The 21700 type cells are extensively used in battery packs, for instance in electric cars, due to their 20 % higher energy density with respect to the former used type 18650 cells. The cells were measured in an ES-ARC from Thermal Hazard Technologies, UK, using the Heat-Wait-Seek test. The generated heat was compared for either fresh cells and cells after cyclic aging. The cyclic aging was performed at 0 °C and 20 °C with a charging rate of 0.3C for 0 °C and 0.7C for 20 °C and a discharging rate of 2C for 20 °C and 0.5C for 0 °C until the state of health was at 80 % ±2 %. The two different temperatures studied in the cyclic aging were chosen as 0 °C to cause lithium plating and as 20 °C to cause a higher internal resistance due to a thicker solid-electrolyte-interface, which has a high influence on the measured properties in the Heat-Wait-Seek test and therefore on the generated heat.With this approach the generated heat in abuse tests can be calculated more accurately to simulate the propagation of heat during a single cell failure in a pack or to calculate the necessary thickness of a heat barrier for safer battery packs. This helps manufacturers to improve their battery pack design with respect to the specific volumetric energy density and safety.

Razrabotka metodik i eksperimental'nykh ustanovok dlya opredeleniya teploemkosti zhelezorudnykh materialov

One of the most important thermophysical pellets characteristics is considered — their heat capacity, which affects the technological production process of iron ore pellets at the stage of their heat treatment in a layer on a conveyor belt. Since the physical heat capacity of materials is determined by the enthalpy value, the mixing method is used to measure the latter, which is implemented on an installation with an adiabatic calorimeter. The research object is Kachkanar pellets of different basicity. The average values of the pellets enthalpy and their physical heat capacity, taking into account changes in the phase and chemical composition of the material, are presented in the interpolation equations form. The temperature dependences of the apparent heat capacity of pellets of various basicity at different heating rates were determined using a newly created experimental setup that allows determining the complex of thermophysical characteristics. Estimates of the enthalpy change and the dependence of the apparent heat capacity on temperature for fluxed and unfluxed concentrates of Sokolovsko-Sarbaysky mining and processing plant were carried out on an experimental installation using the method of quantitative thermal analysis. The presented methods for determining the enthalpy and heat capacity of iron ore pellets and concentrates, as well as the designs created for the implementation of these methods can be used to determine the heat capacities of various materials of metallurgical production and to optimize the operating parameters of their heat treatment.

Thermal Physical Properties of Metals in a Quasi-Two-Phase Model

Abstract—The applicability of the model of a two-phase locally equilibrium region for calculating the temperature dependences of heat capacities, linear thermal expansion coefficients, and thermal diffusivities of various metals is demonstrated. It is shown that the proposed relations make it possible to describe the increase in the thermal characteristic with increasing temperature and its changes associated with the implementation of the phase transition. The possibility of extrapolating the established dependences to experimentally unexplored areas is indicated. The relative simplicity of the established relationships, a certain universality of the model in describing various solids, and the visibility of the theoretical results obtained give hope for the use of the model in engineering and technical calculations.