Temperature Dependence Of Heat Capacity Research Articles

Heat capacity measurements on Ba1.5Fe2(PO4)3 and its thermodynamic functions

The temperature dependence of molar heat capacity of Ba1.5Fe2(PO4)3 phosphate was investigated between T = 6 and 670 K with precision adiabatic vacuum and differential scanning calorimetry. The anomaly was observed in the heat capacity curve, and its character was explained by magnetic disorder–order phase transition at T below 6 K. The standard thermodynamic functions $$C_{{{\text{p}} \cdot {\text{m}}}}^{{\text o}}$$ , $$[H_{\text{m}}^{{\text o}} \left( T \right) - H_{\text{m}}^{{\text o}} \left( 6 \right)]$$ , $$\left[ {S_{\text{m}}^{{\text o}} \left( T \right) - S_{\text{m}}^{{\text o}} \left( 6 \right)} \right]$$ and $$\Phi _{\text{m}}^{{\text o}}$$ of Ba1.5Fe2(PO4)3 were calculated within the range T → 6–670 K. The low-temperature heat capacity analysis, based on the Debye theory and multifractal model, reveals framework structural topology of the studied phosphate.

Anomalous Lattice Properties of Manganese Monosilicide: the Thermodynamic Approach

The temperature dependences of the thermal and elastic MnSi properties are analyzed within the limits of the self-consistent approach. The role of the anharmonicity of acoustic and optical lattice vibrations is analyzed. It is demonstrated that anomalously weak anharmonicity is characteristic for acoustic phonons. In particular, this explains the temperature dependence of the MnSi bulk compressive modulus. The one-electron contribution is estimated and the anomalous non-lattice contribution to the formation of the temperature dependences of heat capacity and volume thermal expansion coefficients.

Energetics of poloxamer micellization at normal and high pressures

Micellization of a poloxamer P105 in diluted aqueous solutions was first investigated by means of high-sensitivity differential scanning calorimetry at different pressures up to ∼160 MPa. The temperature dependence of partial heat capacity of the poloxamer clearly indicates that the unimers have the random coil conformation while the micelles are built of a “dry” PO core and hydrated EO shell. Independently of the polymer concentration, the micellization temperature increases upon increasing pressure while the enthalpy decreases. Based on these dependences, the micellization increments of the partial volume Δtv as well as the coefficients of thermal volume expansion and compressibility, Δtα and Δtχ, of the poloxamer were calculated. They prove that the dehydration of PO hydrophobic blocks makes the main contribution to the micellization energetics. We demonstrate that poloxamer micelles are formed via a nucleation stage of unimer dimerization followed by consecutive energetically favored attachment of unimers to the dimer and further to the growing micelle.

Vibrational Properties of Bulk Boric Acid 2A and 3T Polymorphs and Their Two-Dimensional Layers: Measurements and Density Functional Theory Calculations.

Boric acid (H3BO3) is being used effectively nowadays in traps/baits for the management of Aedes aegypti L. and Aedes albopictus Skuse species of mosquitoes, which are the main spreading vectors worldwide for diseases such as malaria, dengue, and zika. Previously, we published results on the structural, electronic, and optical properties of its molecular triclinic H3BO3-2A and trigonal H3BO3-3T polymorphs within the framework of density functional theory (DFT). Because of the renewed importance of these materials, the focus of this work is on the vibrational properties of the bulk boric acid 2A and 3T polymorphs. We measured the infrared and Raman spectra of the former, which was accompanied and interpreted through state-of-the-art DFT calculations, supplemented by computations regarding the H3BO3 molecule and two-dimensional layers based on the bulk structures. We identify/assign their normal modes and find vibrational signatures for each polymorph as well as in- and out-of-plane motions and molecular vibrations, unveiling a nice agreement between the DFT level of theory employed and our improved spectroscopic measurements in the wavenumber ranges of 400-2000 cm-1 (infrared) and 0-1500 cm-1 (Raman). We show that a dispersion-corrected DFT functional within the generalized gradient approximation (GGA) can be very accurate in describing the vibrational properties of the boric acid polymorphs. Besides, several issues left open/not clearly resolved in previously published works on the vibrational mode assignments of the bulk and 2D sheets of boric acid are explained satisfactorily. Finally, phonon dispersions and associated densities of states were also evaluated for each polymorph along with their temperature-dependent DFT-calculated entropy, enthalpy, free energy, heat capacity, and Debye temperature. In particular, our DFT calculations suggest a possible way to differentiate the 2A and 3T boric acid polymorphs through Raman spectroscopy and heat capacity measurements.

Development of a physical-mathematical model for the process of crystallization of meat systems

It is proven that the complex of processes that occur during freezing-defrosting of meat systems cannot be described within the framework of the theory of freezing out true solutions. A characteristic feature of meat systems is the heterogeneity in terms of chemical composition, structure and properties. Given this, within the framework of the proposed physical-mathematical model for the process of crystallization, meat system is regarded as a colloidal capillary-porous body. In this case, a process of crystallization is considered as the superposition of two processes: freezing out free moisture (basic process) and a competing process for increasing binding energy for the bound moisture. It was established that the aforementioned processes differently depend on temperature: the speed of freezing out moisture decreases with a decrease in temperature while the rate of the competing process, on the contrary, increases. It was theoretically predicted and experimentally proven that a change in the information parameters of effective specific heat capacity is the criterion of reversibility of the process of low temperature treatment. As revealed by computer simulation, the proposed model more adequately reflects the actual character of dependence of the effective specific heat capacity of meat systems with different composition and properties. Based on the proposed physical-mathematical model for the crystallization of meat systems, we have developed a method for determining effective specific heat capacity (C e ) using the thermograms of freezing-defrosting. Information parameters, which were derived from the temperature dependence of effective specific heat capacity, are: t cr/mel is the temperature of maximum rate of crystal formation (melting), oC; Dt cr is the cryoscopic interval of temperatures, oC; DН cr is the specific heat of phase transition in a cryoscopic interval of temperatures, J/K; Dw is the share of moisture, which changes its aggregate state in a cryoscopic interval of temperatures (the amount of free frozen out or melted moisture). The study conducted became the basis for the scientific substantiation of technologies for manufacturing semi-finished frozen minced meat products for the criterion of reversibility

Fundamental thermal properties of polyvinyl alcohol by fast scanning calorimetry

Polyvinyl alcohol (PVA) is a synthetic, semi-crystalline polymer with a wide array of commercial uses ranging from textiles and packaging to medicine. Despite the fact that PVA is in common use, several important thermal properties have not been measured including: 1. temperature dependent liquid state specific heat capacity, cpLiquid(T); 2. specific heat capacity increment of amorphous PVA at the glass transition temperature, Δcpamor(Tg); and, 3. fraction of rigid amorphous phase in semi-crystalline PVA, ϕRA. Two rate-dependent effects have prevented these measurements: PVA thermally degrades at temperatures just in excess of 200 °C which is often within the onset of melting, and PVA crystallizes from the melt so rapidly that it is difficult to obtain fully amorphous polymer. To prevent degradation, and measure these fundamental thermal properties, we have used fast scanning calorimetry at rates ranging from 1000 K/s up to 600,000 K/s. The Mettler Flash DSC1 and a custom-built calorimeter were used to cover this range of heating and cooling rates. We determine the critical cooling rate, βc, needed to quench PVA into an amorphous glass as |βc| = 20,000 K/s. Using FSC in combination with conventional differential scanning calorimetry, we find cpLiquid(T) = ((0.0016 ± 0.0002)*T + (2.3 ± 0.2)) J/(gK). The specific heat capacity increment for fully amorphous PVA is Δcpamor(Tg) = (1.01 ± 0.05) J/(gK). For the semi-crystalline samples used in this study, PVA obeys a two phase model in which ϕRA ∼0. The approaches used in this work are applicable to any semicrystalline polymer or biopolymer which degrades upon heating, or crystallizes so rapidly from the melt that a fully amorphous material cannot be realized.

Теплофизические и диэлектрические свойства Bi-=SUB=-1-x-=/SUB=-Er-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

AbstractThe heat capacity and the permittivity of multiferroics Bi_1 – x Er_ x FeO_3 ( x = 0, 0.10, and 0.15) have been studied in the temperature range 130–800 K. It is found that an insignificant substitution of erbium for bismuth significantly increases the heat capacity in a wide temperature range T > 300 K. The temperature dependence of the excess heat capacity is shown to be due to manifestation of the three-level states. An additional anomaly characteristic of a phase transition has been revealed in the temperature dependences of the heat capacity and the permittivity for the compositions with x = 0.15 at T = 587 K. The results of studies are discussed in combination of the data of structural studies.

Решеточная теплоемкость наноструктурированных материалов на основе титана/циркония и алюминия

AbstractThe dynamic and thermal properties of nanostructured materials based on aluminum with the periodic inclusions of Ti or Zr clusters have been investigated by the method of molecular dynamics. The elastic moduli, spectral vibrational densities of states, and temperature dependences of heat capacity for different Ti–Al and Zr–Al systems have been obtained. The effect of specific features of the phonon spectrum on the heat capacity of the nanocomposite lattice has been examined. It is shown that the ordering type and size of Ti/Zr clusters in the aluminum matrix significantly affect the elastic properties and heat capacity. The results obtained can be used for fabricating new aluminum-, titanium-, and zirconium-based composites with the desired properties.

ФАЗОВАЯ ДИАГРАММА СИСТЕМЫ Na–Na2O

Phase equilibria in the Na–O system are interesting because metallic sodium is widely used as a coolant in nuclear reactors. The aim of this work was the thermodynamic modeling of the Na–O system in the Na–Na2O region, as well as the calculation of the phase diagram of this system. In the course of the study, the available experimental data on the solubility of oxygen in liquid sodium are analyzed. Using literature data, in the course of the study, the phase equilibria were simulated and the coordinates of the phase diagram of the Na–Na2O region were calculated. In the process of the study, the “FactSage” software was used for calculations. The data of the SGPS (SGTE pure substances database) base are used, such as standard enthalpies of formation, standard entropies, and phase transition parameters, as well as temperature dependences of molar heat capacities for solid and liquid substances forming the system (solid and liquid Na; crystalline modifications of Na2O and its melt). Modeling of the Na–Na2O melt is performed by means of the two-sublattice model of ionic liquid. The interaction parameters for this model are determined in the process of the work. Temperature and concentration dependences are expressed by means of the Redlich-Kister polynomial.

Simultaneous Identification of temperature-dependent Thermal Conductivity and Specific Heat Capacity

Simultaneous Identification of temperature-dependent Thermal Conductivity and Specific Heat Capacity

Electronic, thermodynamics and mechanical properties of LaB6 from first-principles

Up to date, the electronic structure properties of amorphous lanthanum hexaboride, a-LaB6, were not yet investigated, and the thermodynamic and mechanical properties of crystalline lanthanum hexaboride (c-LaB6) were studied incompletely. The goal of this work was to fill these gaps in the study of lanthanum hexaborides. The electronic and phonon structures, thermodynamic and mechanical properties of both crystalline and amorphous lanthanum hexaborides (c-LaB6, a-LaB6, respectively) were investigated within the density functional theory. An amorphyzation of c-LaB6 gives rise to the metal – semiconductor transition. The thermal conductivity decreases on going from c-LaB6 to a-LaB6. The elastic moduli, hardness, ideal tensile and shear strengths of a-LaB6 are significantly lower compared to those of the crystalline counterpart, despite the formation of the icosahedron-like boron network in the amorphous phase. For c-LaB6, the stable boron octahedrons are preserved after the failure under tensile and shear strains. The peculiarity in the temperature dependence of heat capacity, Cp(T), at 50 K is explained by the availability of a sharp peak at 100 cm−1 in the phonon density of states of c-LaB6. An analysis of the Fermi surface indicates that this peak is not related to the shape of the Fermi surface, and is caused by the vibration of lanthanum atoms. In the phonon spectrum of a-LaB6, the peak at 100 cm−1 is significantly broader than in the spectrum of c-LaB6, for which reason the anomaly in the Cp(T) dependence of a-LaB6 does not appear. The calculated characteristics are in good agreement with the available experimental data.

Global Regolith Thermophysical Properties of the Moon From the Diviner Lunar Radiometer Experiment

AbstractWe used infrared data from the Lunar Reconnaissance Orbiter (LRO) Diviner Lunar Radiometer Experiment to globally map thermophysical properties of the Moon's regolith fines layer. Thermal conductivity varies from 7.4 × 10−4 W m−1 K−1 at the surface to 3.4 × 10−3 W m−1 K−1 at depths of ~1 m, given density values of 1,100 kg m−3 at the surface to 1,800 kg m−3 at 1 m depth. On average, the scale height of these profiles is ~7 cm, corresponding to a thermal inertia of 55 ± 2 J m−2 K−1 s−1/2 at 273 K, relevant to the diurnally active near‐surface layer, ~4–7 cm. The temperature dependence of thermal conductivity and heat capacity leads to an ~2 times diurnal variation in thermal inertia at the equator. On global scales, the regolith fines are remarkably uniform, implying rapid homogenization by impact gardening of this layer on timescales <1 Gyr. Regional‐ and local‐scale variations show prominent impact features <1 Gyr old, including higher thermal inertia (> 100 J m−2 K−1 s−1/2) in the interiors and ejecta of Copernican‐aged impact craters and lower thermal inertia (< 50 J m−2 K−1 s−1/2) within the lunar cold spots identified by Bandfield et al. (2014). Observed trends in ejecta thermal inertia provide a potential tool for age dating craters of previously unknown age, complementary to the approach suggested by Ghent et al. (2014). Several anomalous regions are identified in the global 128 pixels per degree maps presented here, including a high‐thermal inertia deposit near the antipode of Tycho crater.

Investigation of storage materials for packed bed cold storages in liquid air energy storage (LAES) systems

Liquid air energy storage (LAES) is a storage technology for electric energy, using liquefied air as storage medium. Balancing fluctuating power in- and outputs, storage systems improve the integrability and availability of renewable energies. Due to the high energy density of liquefied gases, the storage volume is small, especially compared to similar storage technologies as pumped hydro or compressed air energy storage.During the charging process, ambient air is liquefied with an adopted Claude-cycle using additional cold from a cold storage. When the electricity demand is high, liquid air is released from the storage tank for power generation in the discharging phase. Therefore, liquid air is pressurized with a cryo-pump, heated up in the cold storage and finally expanded using an air-expander. The cold storage is cooled down to cryogenic temperatures again.Transferring cold from the discharging to the charging phase, the cold storage is one of the key components, influencing the process efficiency of the LAES-system. One option to design the cold storage is a packed bed cold storage (PBCS), which consists of a simple cylinder and a packed bed of storage material. Investigations on thermodynamic properties show that the temperature-dependent heat capacity of the storage material has a major influence on the performance of the cold storage. The influence of different heat capacity characteristics on the performance of the PBCS is systematically analyzed. The resulting theory is applied to existing storage materials and their related heat capacities. Nine storage materials are investigated, ranging from metals to ceramics, minerals and plastics.

The ‘Particle Weighting’ Effect in the Heat Capacity Temperature Dependence of the V$_{2}$D Ordering Interstitial Alloys

The ‘Particle Weighting’ Effect in the Heat Capacity Temperature Dependence of the V$_{2}$D Ordering Interstitial Alloys

Thermodynamic properties of block copolymers of chitosan with poly(D,L-lactide)

In the present work, the temperature dependences of heat capacities of block copolymers of chitosan with poly(D,L-lactide) have been measured in the temperature range from 6 to 350K by precision adiabatic vacuum calorimetry, and thermophysical properties of copolymers have been studied over the range from 270 to 560K by differential scanning calorimetry (DSC). In the above temperature intervals, the glass transition has been detected for all investigated compounds, and the standard thermodynamic characteristics have been determined and analyzed. The standard thermodynamic functions of block copolymers under study, namely, heat capacity Cpo(T), enthalpy [Н°(Т)−Н°(0)], entropy [S°(T)−S°(0)], and Gibbs energy [G°(T)−H°(0)] for the range from T→0 to 350K, and the standard entropies and Gibbs energies of formation at T=298.15K have been calculated based on the obtained experimental data. The standard thermodynamic properties of the investigated compounds have been discussed, and the dependences of thermodynamic properties of block copolymers on their composition have been established.

Thermophysical Properties of Cold- and Vacuum Plasma-Sprayed Cu-Cr-X Alloys, NiAl and NiCrAlY Coatings II: Specific Heat Capacity

Part I of the paper discussed the temperature dependencies of the electrical resistivities, thermal conductivities, thermal diffusivities and total hemispherical emissivities of several vacuum plasma-sprayed (VPS) and cold-sprayed (CS) copper alloy monolithic coatings, VPS NiAl, VPS NiCrAlY, extruded GRCop-84 and as-cast Cu-17(wt.%)Cr-5%Al. Part II discusses the temperature dependencies of the constant-pressure specific heat capacities, C P, of these coatings. The data were empirically regression-fitted with the equation: $${\varvec{C}}_{\mathbf{P}} = {\mathbf{ AT}}^{\mathbf 4} + {\mathbf{BT}}^{\mathbf 3} + {\mathbf{CT}}^{\mathbf 2} + {\mathbf{DT}} + \varvec{E}$$ where T is the absolute temperature and A, B, C, D and E are regression constants. The temperature dependencies of the molar enthalpy, molar entropy and Gibbs molar free energy determined from experimental values of molar specific heat capacity are reported. Calculated values of C P using the Neumann–Kopp (NK) rule were in poor agreement with experimental data. Instead, a modification of the NK rule was found to predict values closer to the experimental data with an absolute deviation less than 6.5%. The specific molar heat capacities for all the alloys did not agree with the Dulong–Petit law, and C P > 3R, where R is the universal gas constant, were measured for all the alloys except NiAl for which C P < 3R at all temperatures.

Thermal properties of spin-S Kitaev-Heisenberg model on a honeycomb lattice

Temperature (T) dependence of heat capacity C(T) in the S=1/2 Kitaev honeycomb model shows a double-peak structure resulting from fractionalization of spins into two kinds of Majorana fermions. Recently it has been discussed that the double-peak structure in C(T) is also observed in magnetic ordered phases of the S=1/2 Kitaev-Heisenberg (KH) model on a honeycomb lattice when the system is located in the vicinity of the Kitaev's spin liquid phase. In addition to the S=1/2 spin case, similar double-peak structure has been confirmed in the KH honeycomb model for classical Heisenberg spins, where spin S is regarded as S→∞. We investigate spin-S dependence of C(T) for the KH honeycomb models by using thermal pure quantum state. We also perform classical Monte Carlo calculations to obtain C(T) for the classical KH model. From obtained results, we find that the origin of the high-temperature peak is different between the quantum spin case with small Ss and the classical Heisenberg spin case. Furthermore, the high-temperature peak in the quantum spin case, which is one of the clues for fractionalization of spins, disappears for S>1.

Advanced Analysis of Isobaric Heat Capacities by Mathematical Gnostics

Two novel imidazolium based ether-functionalized room temperature ionic liquids were synthesized to study the temperature dependence of the isobaric heat capacity in the temperature range 298.15–348.15 K. In-house synthesized ionic liquids are often available in small amounts only, owing to the high cost of the precursors and difficulties during the synthesis itself. It is therefore impossible to repeat measurement many times so that a statistically significant data sample can be obtained. In addition, to obtain at least several values of the measured property, the ionic liquid must be recycled and reused. In this work two recycling techniques were used and their influence on the values of the experimental isobaric heat capacity was analyzed. Advantages of a modern nonstatistical data analysis technique, namely mathematical gnostics, were demonstrated.

Isobaric heat capacity and standard thermodynamic properties of NaLaTiO4 and Na2La2Ti3O10 over the range of (7–670) K

The heat capacities of layered perovskite-like oxides NaLaTiO4 and Na2La2Ti3O10 were measured by precision adiabatic vacuum calorimetry over the temperature range of (7–350) K and by differential scanning calorimetry over the temperature range of (350–670) K. The standard thermodynamic functions: molar heat capacity C p,m, enthalpy H(T) − H(9), entropy S(T) − S(9), and Gibbs energy −[G(T) − G(9)] of the compounds were evaluated from the experimental heat capacity temperature dependences over the range of (9–670) K. The extrapolation of heat capacity down to T = 0 K is incorrect in this case due to the considerable deviation of experimental points from fitting curves obtained on the basis of Debye’s theory.

Thermodynamic properties of misfit cobaltite [Bi2-xCa2O4][CoO2]1.7

We synthetized a misfit structure cobaltite [Bi2-xCa2O4][CoO2]1.7 and studied its thermal behavior by simultaneous thermal analysis (STA), low temperature heat capacity measurement in physical property measurement system (PPMS), differential scanning calorimetry (DSC) to measure heat capacity and drop calorimetry to obtain the relative enthalpy increments. The oxygen non-stoichiometry determined by thermogravimetry (STA data combined with weight loss measurement of the material reduced in hydrogen atmosphere) was analyzed in terms of point defect model resulting in two independent reactions, oxygen release and cobalt disproportionation, described by the respective enthalpy and entropy changes. The applied model satisfactorily describes two regimes of oxygen release/incorporation associated with the respective Co valency changes Co4+/Co3+ and Co3+/Co2+. The temperature dependence of the molar heat capacity above room temperature was derived by simultaneous least squares method from DSC and enthalpy data considering the contribution due to oxygen release and deviation from ideal stoichiometry. The low temperature heat capacity was analyzed in terms of a combined Debye–Einstein model.