Temperature Dependence Of Heat Capacity Research Articles

Dynamics of the crystal structure of tin-based type-I clathrates with different degrees of disorder in their cationic frameworks.

The temperature dependencies of heat capacity, CP(T), and cubic unit cell parameter, a(T), were experimentally obtained in the range of 2-300 K for the compounds Sn24P19.2I8, Sn20Zn4P20.8I8, and Sn17Zn7P22I8, which belong to a family of type-I clathrates. The experimental data were analyzed in the frames of the Debye-Einstein approximation, further accounting for the contributions of positional disorder in the clathrate frameworks as well as those of defect modes arising from the distribution of guest atoms over unequal in energy but close in space positions inside the framework cages. By fitting the experimental data, the Debye and Einstein characteristic temperatures describing the dynamics of the framework and guest atoms, respectively, were obtained. Their analysis revealed peculiar dependencies of the characteristic temperatures upon the number of substituted zinc atoms and the concentration of vacancies in the framework, which are discussed in this paper.

Thermochemistry of sesquiterpene lactone argolide

The enthalpies of dissolution of argolide (C15H20O3) in 96% ethanol are determined by isothermal calorimetry at 298.15 K and different dilutions of 1: 18 000, 1: 36 000, and 1: 72 000 (by mole). The standard enthalpy of dissolution of argolide in 96% ethanol is calculated from the obtained data: (86 ± 17) kJ mol−1. The temperature dependence of heat capacity of C15H20O3 is studied by means of dynamic calorimetry. An equation is derived to describe the С p 0 ~ f (Т) dependence, and the standard heat capacity at 298.15 K is found to be (393 ± 13) J mol−1 K−1. The enthalpies of combustion, fusion and formation of argolide are calculated via approximation.

Does the Boson Peaks Exist in Small Neutral Gold Clusters?

The Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. A well resolved boson peak is observed in the low-frequency portion of the spectrum. A starting point for our discussion is the behaviour of the boson peak, derived from the vibrational density of states and the temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold clusters. This Boson peak is associated with the existence of intermediate range order (IRO) in the arrangements of atoms. The low frequency (Far Infrared FIR, IR-C 200-10 cm−1) containing this dominant spectral line (Boson peak) is interpreted in terms of its relationship to the amplitude and extent of the density fluctuations in atoms and is, thereby, considered a measure of the intermediate range order in these atoms. We found a systematic relation among the boson peak energy, the boson peak intensity per atom, and the zigzag-bond density; the peak energy decreases and the peak intensity increases as zigzag-bond density decreases.

Effect of Size, Temperature, and Structure on the Vibrational Heat Capacity of Small Neutral Gold Clusters

The vibrational heat capacity Cvib of a re-optimized neutral gold cluster was investigated at temperatures 0.5-300 K. The vibrational frequency of an optimized cluster was revealed by small atomic displacements using a numerical finite-differentiation method. This method was implemented using density-functional tight-binding (DFTB) approach. The desired set of system Eigen frequencies (3N -6) was obtained by diagonalization of the symmetric positive semi definite Hessian matrix. Our investigation revealed that the Cvib curve is strongly influenced by temperature, size, and structure and bond-order dependency. The effect of the range of interatomic forces is studied; especially the lower frequencies make a significant contribution to the heat capacity at low temperatures. In addition to that, we have exactly predicted the vibrational frequencies (ωi) which occur between 0.55 to 370.72 cm-1, depending on the nanoparticle morphology at T=0 for small neutral gold clusters AuN=3-20. This result has been proved and confirmed by the size effect values. It was found that beside the particle size, geometric shape, defect structure and an increase in asymmetry of nanoparticles effects on heat capacity. Surprisingly, the Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. Finally, temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold clusters have been studied for the first time.

Mathematical modeling of fish burger baking using fractional calculus

Tilapia (Oreochromis sp.) is the most important and abundant fish species in Brazil due to its adaptability to different environments. The development of tilapia-based products could be an alternative in order to aggregate value and increase fish meat consumption. However, there is little information available on fishburger freezing and cooking in the literature. In this work, the mathematical modeling of the fish burger baking was studied. Previously to the baking process, the fishburgers were assembled in cylindrical shape of height equal to 8mm and diameter 100mm and then baked in an electrical oven with forced heat convection at 150?C. A T-type thermocouple was inserted in the burger to obtain its temperature profile at the central position. In order to describe the temperature of the burger during the baking process, lumped-parameter models of integer and fractional order and also a nonlinear model due to heat capacity temperature dependence were considered. The burger physical properties were obtained from the literature. After proper parameter estimation tasks and statistical validation, the fractional order model could better describe the experimental temperature behavior, a value of 0.91?0.02 was obtained for the fractional order of the system with correlation coefficient of 0.99. Therefore, with the better temperature prediction, process control and economic optimization studies of the baking process can be conducted.

Comprehensive thermodynamic study of methylprednisolone

In the present work the temperature dependence of heat capacity for methylprednisolone has been measured for the first time over the temperature range from 6 to 350K using by precision adiabatic vacuum calorimetry. Based on the experimental data, the thermodynamic functions of the methylprednisolone, namely, the heat capacity, enthalpy H°(T)−H°(0), entropy S°(T)−S°(0) and Gibbs function G°(T)−H°(0) have been evaluated from the experimental values for the range from T→0 to 350K. Standard molar enthalpy of combustion (−11898.9±6.7)kJ·mol−1 of the methylprednisolone was measured for the first time using high-precision combustion calorimeter. The standard molar enthalpy of formation in the crystalline state (−1045.8±7.3)kJ·mol−1 of compound at 298.15K was derived from the combustion experiments. The standard molar enthalpy of sublimation at 298.15K (194.5±2.2)kJ·mol−1 was measured by using the quartz-crystal microbalance (QCM). Using combination of the adiabatic and combustion calorimetry with the result from QCM, the thermodynamic functions of the methylprednisolone at T=298.15K and p=0.1MPa have been calculated.

Thermodynamic and spectroscopic properties of KNbTeO6

In the present work, the temperature dependence of heat capacity of KNbTeO6 has been measured for the first time over the range from 6K to 332K by precision adiabatic vacuum calorimetry. The experimental results were used to calculate standard thermodynamic functions, namely the heat capacity Cpo(T), enthalpy H°(T)−H°(0), entropy S°(T)−S°(0) and Gibbs function G°(T)−H°(0), for the range from T→0K to 332K. The phase transitions and thermal decomposition of KNbTeO6 were determined by differential scanning calorimetry. Structural changes in phase transitions were studied by high-temperature Raman spectroscopy.

Thermophysical properties of Ni based super alloy 617

In this study thermophysical properties of alloy 617 have been measured as a function of temperature using various thermal analysis techniques and complemented by structural and microstructural characterization. The enthalpy increment (HT−H298) has been measured using static calorimetry in the temperature range of 300–1523 K. It is found that (HT−H298) increases monotonically with temperature up to about 1000 K. However, above this temperature two distinct inflections are detected at about 1030 K and 1205 K respectively. A critical comparison of these inflections with Thermo-Calc simulations and dynamic calorimetry measurements indicates that they are associated with dissolution of M23C6, and γ′-Ni3Al phases respectively. The enthalpy data has been numerically fitted using non-linear regression analysis to obtain the temperature dependence of heat capacity. Further, the thermal diffusivity and thermal expansivity of alloy 617 have been measured using the laser flash method and thermo-mechanical analyzer in the temperature range of 300–1523 K. Finally, with the knowledge of heat capacity, density and thermal diffusivity data, thermal conductivity has also been estimated in the temperature range of 300–1523 K. The measured properties for alloy 617 have been compared with Thermo-Calc, JMatPro simulation and other literature data, which clearly establishes the role of precipitates dissolution. The various properties measured in the present study are original and new addition to the database for alloy 617, which can serve as new input for Thermo-calc based optimization. This paper also provides the insight into the temperature and composition dependence of thermal conductivity of alloy 617.

Tunable magnetism and structural transformations in mixed light- and heavy-lanthanide dialuminides

Rare-earth intermetallics play a critical yet often obscure role in numerous technological applications, including sensors, actuators, permanent magnets, and rechargeable batteries; therefore, understanding their basic science is of utmost importance. Here we report structural behaviors, specific heat, and magnetism of $\mathrm{P}{\mathrm{r}}_{1\text{--}x}\mathrm{E}{\mathrm{r}}_{x}\mathrm{A}{\mathrm{l}}_{2}$ studied by means of temperature-dependent x-ray powder diffraction, heat capacity, and magnetization measurements, in addition to first-principles calculations. Although the cubic lattice of $\mathrm{PrA}{\mathrm{l}}_{2}$ distorts tetragonally at the Curie temperature ${T}_{C}$, the distortion is rhombohedral in $\mathrm{ErA}{\mathrm{l}}_{2}$, creating a potential for instability in the pseudobinary $\mathrm{PrA}{\mathrm{l}}_{2}\text{\ensuremath{-}}\mathrm{ErA}{\mathrm{l}}_{2}$ system. When $0.05\ensuremath{\le}x\ensuremath{\le}0.5$, materials show complex magnetization behaviors, including metamagnetic transitions and Griffith-like phase. Unique among other mixed-lanthanide dialuminides, the substitution of Er for Pr in $\mathrm{P}{\mathrm{r}}_{1\text{--}x}\mathrm{E}{\mathrm{r}}_{x}\mathrm{A}{\mathrm{l}}_{2}$ results in unexpected ferrimagnetic behavior, and the ferrimagnetic interactions become strongest around $x=0.25$, where the compound shows unusual metamagnetic like transitions observed only in the odd-numbered quadrants of the full magnetic field cycles. The electronic structure calculations, including exchange interactions and crystal field splitting, magnetic moments, anisotropic $4f$ energy density, and magnetic surface potentials rationalize the interesting physics observed experimentally.

Effect of long- and short-range interactions on the thermodynamics of dipolar spin ice

The thermodynamic properties of dipolar spin ice on square, honeycomb and shakti lattices in the long-range and short-range dipole interaction models are studied. Exact solutions for the density of states, temperature dependencies of heat capacity, and entropy are obtained for these lattices with a finite number of point dipoles by means of complete enumeration. The magnetic susceptibility and average size of the largest low-energy cluster are calculated for square spin ice by means of Wang–Landau and Metropolis methods. We show that the long-range interaction leads to a blurring of the energy spectrum for all considered lattices. The inclusion of the long-range interaction leads to a significant change in the thermodynamic behaviour. An additional peak of heat capacity appears in the case of the honeycomb lattice. The critical temperature shifts in the direction of low or high temperatures; the direction depends on the lattice geometry. The critical temperature of the phase transition of square spin ice in the long-range model with frustrated ground states is obtained with the Wang–Landau and Metropolis methods independently.

Computational insight on the structural, mechanical and thermal properties of Cu2CdSnSe4 and Cu2HgSnSe4 adamantine materials

Through first-principles calculation based on the density functional theory (DFT) within the pseudo potential-plane wave (PP-PW) approach, we studied the structural, mechanical and thermal properties of Cu$_2$CdSnSe$_4$ and Cu$_2$HgSnSe$_4$ adamantine materials. The calculated lattice parameters are in good agreement with experimental and theoretical reported data. The elastic constants are calculated for both compounds using the static finite strain scheme. The hydrostatic pressure action on the elastic constants predicts that both materials are mechanically stable up to 10 GPa. The polycrystalline mechanical parameters, i.e., the anisotropy factor ($A$), bulk modulus ($B$), shear modulus ($G$), Young's modulus ($E$), Lame's coefficient ($\lambda$) and Poisson's ratio ($\nu$) have been estimated from the calculated single crystal elastic constants. The analysis of $B/G$ ratio shows that the two studied compounds behave as ductile. Based on the calculated mechanical parameters, the Debye temperature and the thermal conductivity have been probed. In the framework of the quasi-harmonic approximation, the temperature dependence of the lattice heat capacity of both crystals has been investigated.

ChemInform Abstract: Discovery of a Superconducting Cu—Bi Intermetallic Compound by High‐Pressure Synthesis.

AbstractPolycrystalline Cu11Bi7 is prepared by hot press annealing of ball milled stoichiometric mixtures of the elements (BN crucible in multianvil press, 6 GPa, 530—570 °C, 1 h).

Thermodynamic properties of a liquid crystal carbosilane dendrimer

The temperature dependence of the heat capacity of a first-generation liquid crystal carbosilane dendrimer with methoxyphenyl benzoate end groups is studied for the first time in the region of 6–370 K by means of precision adiabatic vacuum calorimetry. Physical transformations are observed in this interval of temperatures, and their standard thermodynamic characteristics are determined and discussed. Standard thermodynamic functions Cp°(T), H°(T) − H°(0), S°(T) − S°(0), and G°(T) − H°(0) are calculated from the obtained experimental data for the region of Т → 0 to 370 K. The standard entropy of formation of the dendrimer in the partially crystalline state at Т = 298.15 K is calculated, and the standard entropy of the hypothetic reaction of its synthesis at this temperature is estimated. The thermodynamic properties of the studied dendrimer are compared to those of second- and fourth-generation liquid crystal carbosilane dendrimers with the same end groups studied earlier.

Material Evaluation and Process Optimization of CNT-Coated Polymer Powders for Selective Laser Sintering.

Multi-walled carbon nanotubes (CNTs) as nano-reinforcements were introduced to facilitate the laser sintering process and enhance the thermal and mechanical properties of polymeric composites. A dual experimental-theoretical method was proposed to evaluate the processability and predict the process parameters of newly developed CNT-coated polyamide 12 (CNTs/PA12) powders. The thermal conductivity, melt viscosity, phase transition and temperature-dependent density and heat capacity of PA12 and CNTs/PA12 powders were characterized for material evaluation. The composite powders exhibited improved heat conduction and heat absorption compared with virgin polymer powders, and the stable sintering range of composite powders was extended and found to be favourable for the sintering process. The microstructures of sintered composites revealed that the CNTs remained at the powder boundaries and formed network architectures, which instantaneously induced the significant enhancements in tensile strength, elongation at break and toughness without sacrificing tensile modulus.

Thermodynamic properties of pyrochlore-like rare earth triple oxides CaLa2MoO7 and MgLa2MoO7

The temperature dependence of the heat capacity of pyrochlore-like compounds CaLa2MoO7 and MgLa2MoO7 has been investigated over the range of 4.4–320 K by adiabatic calorimetry. The main thermodynamic functions and fractal properties of the compounds over the range of 5–320 K have been determined based on the experimental data. We have revealed the heat capacity anomaly in the sample CaLa2MoO7 in the area below 10 K. Standard thermodynamic functions at T = 298.15 K are: for CaLa2MoO7 C p,m(298.15) = 222.1 ± 0.4 J mol−1K−1, S m(298.15) = 246.0 ± 0.8 J mol−1K−1, H m(298.15)−H m(0) = 39.20 ± 0.10 kJ mol−1; for MgLa2MoO7 C p,m(298.15) = 216.6 ± 0.3 J mol−1K−1, S m(298.15) = 231.1 ± 0.6 J mol−1K−1, H m(298.15) − H m(0) = 37.09 ± 0.08 kJ mol−1.

Thermophysical properties of model compounds of the lignin structural unit

Sixteen lignin related aromatic compounds formed by the thermal degradation of lignin and being potentially valuable products of the processing of renewable raw materials were studied using differential scanning calorimetry. The temperatures, enthalpies, and entropies of melting were determined. The temperature dependences of isobaric heat capacities for the studied compounds were obtained. The relationship between the structures of the lignin related compounds and their thermochemical properties is considered.

Discovery of a Superconducting Cu–Bi Intermetallic Compound by High‐Pressure Synthesis

A new intermetallic compound, the first to be structurally identified in the Cu-Bi binary system, is reported. This compound is accessed by high-pressure reaction of the elements. Its detailed characterization, physical property measurements, and ab initio calculations are described. The commensurate crystal structure of Cu11 Bi7 is a unique variation of the NiAs structure type. Temperature-dependent electrical resistivity and heat capacity measurements reveal a bulk superconducting transition at Tc =1.36 K. Density functional theory calculations further demonstrate that Cu11 Bi7 can be stabilized (relative to decomposition into the elements) at high pressure and temperature. These results highlight the ability of high-pressure syntheses to allow for inroads into heretofore-undiscovered intermetallic systems for which no thermodynamically stable binaries are known.

Thermodynamic Properties at Saturation Derived from Experimental Two-Phase Isochoric Heat Capacity of 1-Hexyl-3-methylimidazolium Bis[(trifluoromethyl)sulfonyl]imide.

New measurements are reported for the isochoric heat capacity of the ionic liquid substance 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C6mim][NTf2]). These measurements extend the ranges of our earlier study [N.G. Polikhronidi et al., Phys. Chem. Liq. 52, 657 (2014)] by 5 % of the compressed liquid density and by 75 kelvins. An adiabatic calorimeter was used to measure one-phase (CV1) liquid and two-phase (CV2) liquid + vapor isochoric heat capacities, densities (ρS ), and phase-transition temperatures (TS ) of the ionic liquid (IL) substance. The combined expanded uncertainty of the density ρ and isochoric heat capacity CV measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 0.15 % and 3 %, respectively. Measurements are concentrated in the immediate vicinity of the liquid + vapor phase transition curve, in order to closely observe phase transitions. The present measurements and those of our earlier study are analyzed together, and are presented in terms of thermodynamic properties (TS, ρS, CV1 and CV2) evaluated at saturation and in terms of key derived thermodynamic properties Cp, CS, [Formula: see text], and [Formula: see text] on the liquid + vapor phase transition curve. A thermodynamic relation by Yang and Yang is used to confirm the internal consistency of measured two-phase heat capacities CV2, which are observed to fall perfectly on a line as a function of specific volume at a constant temperature. The observed linear behavior is exploited to evaluate contributions to the quantity CV2 = f(V,T) from chemical potential [Formula: see text] and from vapor pressure [Formula: see text]. The physical nature and specific details of the temperature and specific volume dependence of the two-phase isochoric heat capacity and some features of the other derived thermodynamic properties of IL at liquid saturation curve are considered in detail.

Strong correlation effect on the thermodynamic and mechanical properties of ytterbium dihydride

The strong correlation effect of the thermodynamic and mechanical properties of the Pnma and Fm-3m phases of ytterbium dihydride (YbH2) has been investigated using density functional theory plus Hubbard U method. The equilibrium geometries, elastic constants, various moduli, Poisson's ratio, and elastic wave velocities of the two phases of YbH2 are systematically studied. The Pnma and Fm-3m phases of YbH2 exhibit brittle characteristics. Phonon calculations verify that the two phases are thermodynamically stable. The low-frequency region of the two phases share similar features, whereas the high-frequency region shows a remarkable difference between the two phases. Given the phonon contribution to the Helmholtz free energy, the temperature dependences of equilibrium volume, bulk modulus, entropy, and heat capacity at constant pressure are obtained using quasiharmonic approximation. The calculated trends of equilibrium volume and head capacity at constant pressure are consistent with experimental data.

An approach to improve energy performance of electric vehicle: Theoretical evaluation of electric motor winding heat capacity and electrical resistivity using Debye and Bloch-Gruneisen approximations

New analytical accurate approximations to the evaluation temperature dependence of heat capacity and electrical resistivity of motor winding are presented. The approach is based on the Debye method and Bloch-Gruneisen theory for controlling the heat capacity and electrical resistivity of motor winding with variation of temperature. This analytical evaluation is general and it shows that the results of motor winding heat capacity and resistivity are satisfactory for the wide range temperature variations. Comparison of the calculation results with the other literature data show that our approach is accurate and efficient.