High-temperature Heat Capacity Research Articles

K8CaSi10O25 – Synthesis, in-situ high-temperature single-crystal diffraction and heat capacity

Different sol-gel routes were tested to synthesize polycrystalline material of K8CaSi10O25. The best result in terms of phase purity was obtained using combustion synthesis with glycine as fuel. Single crystals were obtained from the devitrification of a glass. Cyclic single-crystal diffraction studies were carried out within the temperature range of ambient conditions to 873 K with different cooling rates. The crystal structure (space group R3c) at ambient temperature was consistent with previous investigations (a = 11.1135(6) Å, c = 21.9286(14) Å, V = 2345.5(2) Å3). A new high-temperature polymorph was discovered, showing the following crystallographic data at 873 K: space group R3‾m, a = 11.2251(8) Å, c = 11.1789(9) Å, V = 1219.9(2) Å3. On heating, an incommensurately modulated structure was observed between the two aforementioned modifications. The standard third-law entropy was determined from low-temperature Cp’s measured by relaxation calorimetry and amounts to S°(298 K) = 898.7 ± 6.3 J mol−1 K−1.

Effect of temperature on thermal properties and residual strength of coal gangue concrete

Key factors for assessing the high-temperature resistance of coal gangue concrete are high-temperature residual strength and thermal properties. The high-temperature residual strength, high-temperature thermal conductivity, high-temperature specific heat capacity, and high-temperature density of concrete with various coal gangue coarse aggregate replacement ratios were tested using experimental methods in this paper to study the high-temperature resistance of coal gangue concrete. Thermal density and high-temperature residual strength tests took into account influencing factors like the water-cement ratio (0.50, 0.45, 0.40), aggregate replacement ratio (0, 25 %, 50 %, 75 %, 100 %), and temperature variation (room temperature, 200 °C，300 °C，400 °C，500 °C，600 °C，700 °C，800 °C), while thermal properties tests considered the effects of various coarse aggregate replacement ratios and temperatures. The study showed that when the temperature rises, coal gangue concrete's thermal density falls, mass loss rises, residual strength declines, thermal conductivity rises, and its specific heat capacity fluctuates. At temperatures between 20 °C and 400 °C, concrete's residual strength decreases with an increase in the coal gangue coarse aggregate replacement ratio, while thermal conductivity and specific heat capacity increase. At temperatures between 500 °C and 800 °C, however, concrete's residual strength slightly improves with an increased coal gangue coarse aggregate replacement ratio, while mass loss changes more. The research finally provides the formulae for calculating the high-temperature residual strength and thermal properties of coal gangue concrete based on the test results.

Synthesis and High-Temperature Heat Capacity of LaMgAl11O19 and SmMgAl11O19 Hexaaluminates

The processes occurring during heating of a stoichiometric mixture of lanthanum, samarium, magnesium, and aluminum hydroxides synthesized by the reverse precipitation method have been studied by DTA/TG and X-ray powder diffraction methods. The conditions for the synthesis of single-phase LaMgAl11O19 and SmMgAl11O19 samples of the magnetoplumbite structure type have been determined, and the isobaric heat capacity has been measured in the temperature range 317–1817 K, showing the absence of structural transformations in this range.

Synthesis and High-Temperature Heat Capacity of LaMgAl11O19 and SmMgAl11O19 Hexaaluminates

Synthesis and High-Temperature Heat Capacity of LaMgAl11O19 and SmMgAl11O19 Hexaaluminates

Low- and high-temperature heat capacity of metallic technetium

The heat capacity of technetium metal has been measured from 2.1 K to 293 K using relaxation calorimetry and the enthalpy increment up to 1700 K using drop calorimetry. The low-temperature calorimetry measurements revealed a superconducting transition temperature of TC = (7.76 ± 0.08) K. The zero-degree Debye temperature(θE) and the electronic heat capacity coefficient (γe) of the normal state were derived as (307 ± 5) K and (4.22 ± 0.20) mJ·K−2·mol−1, respectively. The standard entropy of the superconducting standard state was derived as Sm° (298.15) = (36.8 ± 1.3) J·K−1·mol−1. The fitting of enthalpy-increment data together with high-temperature heat capacity data reported in literature yielded a heat capacity equation up to 1700 K.

High-Temperature Heat Capacity and Thermodynamic Functions of the LiNaGe4O9 Germanate

High-Temperature Heat Capacity and Thermodynamic Functions of the LiNaGe4O9 Germanate

Oxygen diffusion in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2

This study evaluates the self-diffusion and chemical diffusion coefficients of oxygen in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2 using point defect chemistry (oxygen vacancies and interstitials). The self-diffusion coefficient changed in proportion to the 1/n power of oxygen partial pressure, similar to the defect concentration. All parameters used to represent the diffusion coefficients were determined, and the experimental data were accurately stated. The defect formation and migration energies of the oxides were compared, and the change in Frenkel defect concentration was found to affect the high-temperature heat capacities of CeO2 and ThO2. The oxygen chemical diffusion was evaluated in the oxides, excluding the line compound ThO2, and the coefficients increased dramatically around the stoichiometric composition, i.e., the chemical diffusion coefficient was much higher at stoichiometric composition, with the oxygen-to-metal ratio equal to 2.00, than in low oxygen-to-metal oxides. This difference altered the mechanism of the reduction and oxidation processes. In the reduction process, the chemical diffusion control rate was dominant and a new phase with the oxygen-to-metal ratio equal to 2.00 was formed, which then expanded from the surface in the oxidation process from a low oxygen-to-metal ratio to the stoichiometric composition.

Order and disorder, crossovers, and phase transitions in dipolar artificial spin ice on the Cairo lattice.

We study the thermodynamic properties of the magnetic dipolar spin ice on a 2D pentagonal Cairo lattice by using the numerical Metropolis and the complete enumeration methods. We use the model of point Ising-like dipoles considering long-range interactions with up to 100 nearest neighbors and with periodic boundary conditions. There are two explicit peaks both in the temperature behavior of the heat capacity and in the magnetic susceptibility. The low-temperature peak is caused only by long-range interactions and is not present in the model where each dipole interacts only with four nearest neighbors. The height of the peak depends logarithmically on the quantity of dipoles, which indicates a phase transition. The nature of the low-temperature phase transition is related to the transformation from order to disorder in orthogonal sublattices while maintaining the spin ice state and the spin ice rule in the sublattice of crosses. The high-temperature heat capacity peak is associated with the melting of spin ice, i.e., with the crossover from spin ice to paramagnetic chaos. Its height is constant and does not depend on the quantity of dipoles. It is shown that the choice of the radius of the dipole-dipole interaction has a significant effect on the statistical properties of the model. The model may even show the appearance of the long-range order and the phase transition in the case of long-range interaction or its absence in the case of short-range interaction.

Thermodynamic properties of the novel photocatalyst BiSbO4 phase determined from 1.8 K to 1073 K

Growing interest in BiSbO4 application as the superior photocatalytic material leads to the problem of its thermodynamic stability. However, its thermodynamic properties have not been determined so far. In order to provide this data five experimental methods followed by critical data evaluation were used. BiSbO4 samples were obtained by the solid state synthesis. Low-temperature heat capacity data were obtained with physical property measurement system (PPMS) and standard entropy S0298.15 = 127.1 (±2.0) J/(mol·K) was derived. Next, using differential thermal analysis/differential scaning calorimetry method (DTA/DSC), high-temperature heat capacity of BiSbO4 phase has been measured and is given in the form of Maier-Kelley equation. Metal oxide equilibration established three phase equilibrium characterized by constant temperature and pO2. Finally, employment of the e.m.f. cell with the solid electrolyte gave Gibbs free energy change of the reaction Bi + O2+ 1/2Sb2O4 = BiSbO4. Then, the Third Law analysis provided the standard heat of formation of BiSbO4 from elements equal to ΔH0f,298.15 = −859.50 (±3.57) kJ/mole. This set of thermodynamic data allowed the calculation of the oxide Cp, heat content, S0T and μ0T, which are given in the range of temperature from 298.15 to 1100 K.

Reassessment of thermochemical energy storage in perovskite-like manganites at comparative studies of RP SrCa3Mn3O10-δ vs. orthorhombic Sr0.25Ca0.75MnO3-δ

The structural stability, thermal expansion, oxygen exchange thermodynamics, and thermochemical storage (TCS) capacity of perovskite-like Sr0.25Ca0.75MnO3-δ and Ruddlesden-Popper SrCa3Mn3O10-δ manganites are studied by the combined use of experimental techniques, thermodynamic modeling of the defect formation reactions, and energy calculations utilizing density functional theory (DFT). It is argued that conservative estimates of the storage capacity can be made by the use of the Dulong-Petit limit for high-temperature heat capacity and oxygen partial enthalpy independent of both temperature and oxygen content. The respectively recalculated literature data and the obtained results show that the thermodynamic limit for the TCS capacity (~800 kJ/kg) of Sr0.25Ca0.75MnO3-δ is one of the highest at thermal cycling within the oxygen partial pressure range of 10 −4–0.21 atm. At the same time, the storage capacity of SrCa3Mn3O10-δ achieves only about 600 kJ/kg. The TCS cycling tests demonstrate the stability of SrCa3Mn3O10-δ while a decline in the energy storage capacity is observed for Sr0.25Ca0.75MnO3-δ. According to the EDX analysis, this effect may reflect surface degradation of Sr0.25Ca0.75MnO3-δ. The energy storage capacities of SrCa3Mn3O10-δ and Sr0.25Ca0.75MnO3-δ decrease to 510 and 560 kJ/kg, respectively, because of the rather sluggish reduction kinetics. It is concluded that further improvement of manganites as energy storage materials can be achieved using new doping strategies.

Crystal structure, phase transitions, and thermodynamic properties of magnesium metavanadate (MgV2O6)

As a promising anode material for magnesium ion rechargeable batteries, magnesium metavanadate (MgV2O6) has attracted considerable research interest in recent years. A MgV2O6 sample was synthesized via a facile solid-state reaction by multistep-firing stoichiometric mixtures of MgO and V2O5 powder under an air atmosphere. The solid-state phase transition from α-MgV2O6 to β-MgV2O6 occurred at 841 K and the enthalpy change was 4.37 ± 0.04 kJ/mol. The endothermic effect at 1014 K and the enthalpy change was 26.54 ± 0.26 kJ/mol, which is related to the incongruent melting of β-MgV2O6. In situ XRD was performed to investigate phase transition of the as-prepared MgV2O6 at high temperatures. The cell parameters obtained by Rietveld refinement indicated that it crystallizes in a monoclinic system with the C2/m space group, and the lattice parameters of a = 9.280 Å, b = 3.501 Å, c = 6.731 Å, β = 111.76°. The solid-state phase transition from α-MgV2O6 to β-MgV2O6 was further studied by thermal kinetics, indicating that this process is controlled first by a fibril-like mechanism and then by a spherulitic-type mechanism with an increasing heating rate. Additionally, the enthalpy change of MgV2O6 at high temperatures was measured utilizing the drop calorimetry, heat capacity was calculated and given as: Cp = 208.3 + 0.03583T-4809000T−2 (298 – 923 K) (J mol−1 K−1), the high-temperature heat capacity can be used to calculate Gibbs free energy of MgV2O6 at high temperatures.

High-Temperature Heat Capacity and Thermodynamic Properties of the CaY2Ge3O10 and CaY2Ge4O12 Germanates

High-Temperature Heat Capacity and Thermodynamic Properties of the CaY2Ge3O10 and CaY2Ge4O12 Germanates

Synthesis, Crystal Structure and Thermodynamic Properties of Apatite-like Lead Gadolinium Vanadato-germanates

The Pb10-xGdx(GeO4)2+x(VO4)4-x (x = 0.5, 1.0) apatites were synthesized by the solid-phase synthesis by roasting stoichiometric mixtures of PbO, Gd2O3, GeO2, and V2O5 in air at temperatures of 773–1073 K. Their crystal structure was determined using X‑ray diffraction analysis. The high-temperature heat capacity (350–1000 K) was measured by differential scanning calorimetry. The experimental data Cp = f (T) were used to calculate the thermodynamic properties of apatites

Defect-Induced Properties and Thermodynamics of La0.5Ba0.5CoO3–δ

The defect structure model of La0.5Ba0.5CoO3–δ was successfully verified using a combined set of coulometric and thermogravimetric data. The results were used to model the dependences of Seebeck coefficient, measured vs T and pO2 simultaneously with the total conductivity, and chemical strain of this oxide. The partial molar enthalpy of oxygen in La0.5Ba0.5CoO3–δ was calculated from the defect structure model and used to evaluate the enthalpy increments and high-temperature heat capacity of an oxide with constant chemical composition, La0.5Ba0.5CoO2.99, from the drop calorimetric measurement results in air. The standard enthalpies of formation of cubic La0.5Ba0.5CoO2.95 and double LaBaCo2O5.90 perovskites, and the enthalpy of cation ordering in A-sublattice of La0.5Ba0.5CoO2.95, were found using the results of solution calorimetry at 298.15 K. With the data obtained, we predicted the chemical compatibility of La0.5Ba0.5CoO3–δ with solid oxide fuel cell (SOFC) electrolyte materials.

Density-functional-theory predictions of mechanical behaviour and thermal properties as well as experimental hardness of the Ga-bilayer Mo2Ga2C

Mo2Ga2C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties. To understand this unique MAX phase structure and promote possible future applications, the structure, chemical bonding, and mechanical and thermodynamic properties of Mo2Ga2C were investigated by first-principles. Using the “bond stiffness” model, the strongest covalent bonding (1162 GPa) was formed between Mo and C atoms in Mo2Ga2C, while the weakest Ga-Ga (389 GPa) bonding was formed between two Ga-atomic layers, different from other typical MAX phases. The ratio of the bond stiffness of the weakest bond to the strongest bond (0.33) was lower than 1/2, indicating the high damage tolerance and fracture toughness of Mo2Ga2C, which was confirmed by indentation without any cracks. The high-temperature heat capacity and thermal expansion of Mo2Ga2C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K. Because of the metal-like electronic structure, the electronic excitation contribution became more significant with increasing temperature above 300 K.

Synthesis, crystal structure and thermodynamic properties of apatite Pb-=SUB=-3-=/SUB=-Bi-=SUB=-2-=/SUB=-(GeO_4)-=SUB=-3-=/SUB=-

Apatite Pb3Bi2(GeO_4)3 was obtained by the solid-phase method from the initial oxides of PbO, Bi2O3 and GeO2 by sequential firing in air at temperatures of 773-1003 K. Its crystal structure has been refined by X-ray diffraction. The high-temperature heat capacity (350-1000 K) of this compound was measured by differential scanning calorimetry. Based on these data, the main thermodynamic functions are calculated. Keywords: apatite bismuth-lead germanate, solid-phase synthesis, high-temperature heat capacity, thermodynamic properties Keywords: apatite bismuth-lead germanate, solid-phase synthesis, high-temperature heat capacity, thermodynamic properties.

Synthesis, crystal structure and high-temperature heat capacity of substituted apatites Pb-=SUB=-9-=/SUB=-R(GeO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=- (R=Tb, Dy, Ho)

Pb9R(GeO4)3(VO4)3 (R=Tb, Dy, Ho) apatites were obtained by solid-phase synthesis from the initial oxides of PbO, Tb2O3 (Dy2O3, Ho2O3), GeO2 and V2O5 by sequential annealing (at a temperature of 773-1073 K) in an air atmosphere. Their crystal structure has been determined by X-ray diffraction analysis. The high-temperature heat capacity was measured by differential scanning calorimetry. Based on the experimental dependence of the heat capacity on the temperature, the thermodynamic properties are calculated. Keywords: apatites, solid-phase synthesis, crystal structure, heat capacity, thermodynamic properties. Keywords: apatites, solid-phase synthesis, crystal structure, heat capacity, thermodynamic properties.

Crystal structure and thermodynamic properties of germanate CuEu-=SUB=-2-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-8-=/SUB=-

Copper-europium germanate CuEu2Ge2O8 was obtained from the initial CuO, Eu2O3 and GeO2 oxides using solid-phase synthesis by annealing in air in the temperature range of 1223-1273 K. Its crystal structure was determined (space group Cm). The influence of temperature on high-temperature heat capacity of the synthesized germanate was studied by the differential scanning calorimetry method. It was found that the dependence of heat capacity on temperature has an extreme value related to a phase transition. The thermodynamic properties were calculated based on the experimental data about heat capacity. Keywords: copper-europium germanate, solid-phase synthesis, crystal structure, thermodynamic properties.

A calorimetric and thermodynamic investigation of strontium fluorapatite [formula omitted

A calorimetric and thermodynamic investigation of one of the representatives of full-substituted fluorapatites, strontium-substituted fluorapatite {Sr10PO46F2}, was undertaken. The phase was synthesized according to the technique developed by the authors of the article based on the classical sol–gel process. The synthetic product was characterized by X-ray powder diffraction (XRD), X-ray fluorescence analysis (XRF), Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and Differential thermal/gravimetric analysis (DTA-TG). The enthalpy of formation of the phase was determined using HNO3-solution calorimetry giving ΔfHmo(T=298.15K,Sr10PO46F2,cr)=(-13721±8)kJ∙mol-1. The low-temperature heat capacity, Cp,mo, was measured using adiabatic calorimetry from T = (6.8 to 307.0) K. The high-temperature heat capacity, Cp,mo, was measured using DSC calorimetry from T = (306.7 to 651.7) K. Using these Cp,mo(T) data, the third law entropy at T = 298.15 K, Smo, is calculated as (938.7 ± 3.8) J∙K−1∙mol−1. This new experimental result, together with literature data, are used to calculate the Gibbs energy of formation, ΔfGmo, giving: ΔfGmo(T=298.15K,Sr10PO46F2,cr)=(-13000±9)kJ∙mol-1. Smoothed Cp,moT values between T → 0 K and T = 650 K are presented, along with values for Smo and the functions [HmoT-Hmo0] and [GmoT-Gmo0]. Thermodynamic stability of cation-substituted fluorapatites, M10PO46F2 with M = Ca, Ba, Sr, Mg, was analyzed based on literature and experimental data.

Schottky-like anomaly in the heat capacity and magnetocaloric effect of charge-ordered single-crystalline (Sm, Ca, Sr)MnO[formula omitted] compound

We present a comprehensive experimental study on the magnetic and magnetocaloric properties of a charge-ordered single-crystalline Sm0.5Ca0.25Sr0.25MnO3 compound. The studies on x-ray photoelectron spectroscopy (XPS) reveals the presence of an equal distribution of Mn3+ and Mn4+ ions in the studied system. The Oxygen, O1s-core level spectra have been simulated with three binding energies curves, which correspond to the O2− ions, O1− ions, and chemically adsorbed oxygens, Ochem. The XPS analysis of the O1s-core-level spectra and magnetic characterizations indicate the proper stoichiometry of the present sample. Considering the change of volume phase fraction in the isofield magnetization measurements during the first-order magnetic phase transition from paramagnetic state to ferromagnetic state, the isothermal magnetic entropy change (ΔS) has been estimated based on the modified Clausius–Clapeyron equation. An inverse magnetocaloric effect has also been noticed in the -ΔS vs. T plot calculated by Maxwell’s thermodynamic relation, suggesting the dominant antiferromagnetic ground state supported by a charge-ordered phase of the studied system. The high-temperature zero-field heat capacity (CP) data can be well-interpreted quantitatively using the Debye model of heat capacity. With the extracted magnetic heat capacity (Cmag) data, the temperature variation of the magnetic entropy (S(0)), as well as the adiabatic temperature change (ΔTad), have been estimated. In addition to that, the low-temperature CP data displays a Schottky-like anomaly in the temperature region between 2 K and 20 K. The experimental data points are successfully fitted by considering the various contributing factors of the low-temperature heat capacity such as the lattice-phonon vibration (Clat), antiferromagnetic spin-wave (Cmag), and the two-level Schottky function (Csch) due to the energy splitting of the Sm3+ cations.