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1.
Enthalpy increment measurements on CeTe2O6 (s) and ThTe2O6 (s) were carried out using a Calvet micro-calorimeter. The enthalpy increment values were least squares analyzed, with the constraint that H0(T)−H0 (298.15 K) at 298.15 equals 0 and Cp0 (298.15 K) is equal to the value estimated by Kellog’s method.The dependence of the enthalpy increment with temperature can be given as:Molar heat capacity Cp0(T), S(T) and Gibb’s free energy functions were evaluated. 相似文献
H0(T)−H0 (298.15 K)(J mol−1)=189.95 T (K)+15.226×10−3 T2 (K) +15.414×105/T (K)−63157 (CeTe2O6 (s), 391.5–848.0 K)
H0(T)−H0 (298.15 K)(J mol−1)=191.34 T (K)+14.993×10−3 T2 (K) +14.668×105/T (K)−63300 (ThTe2O6 (s), 391.5–909.3 K)
2.
The standard enthalpies of formation at 300 K of the RNiAl phases (R=rare earth) have been obtained by using a high temperature direct reaction drop calorimeter and an aneroid isoperibol calorimeter. State and composition of the samples were checked by X-ray diffraction analysis. Metallographic examination was performed and the phases were further identified by electron microscopy and electron probe microanalysis. The results obtained are discussed and compared with those available for the binary RNi2 and RAl2 compounds. 相似文献
3.
J. wik T. Palewski K. Nenkov G.S. Burkhanov O.D. Chistyakov J. Klamut J. Warchulska 《Journal of Alloys and Compounds》2008,460(1-2):41-46
The standard Gibbs energy of formation, , of MgLa in the temperature range from near absolute 0 to 525 K were determined by calorimetry. The heat capacities, Cp, from 2 K to 525 K were measured by the relaxation method and DSC. Also, a thermal anomaly at 5.9 K, which appeared to be a superconductive phase transition, was found in the obtained Cp values. The values were determined by combining the Cp data with the standard enthalpy of formation at 298 K which was measured by the Calvet-type calorimeter using hydrochloric acid solution. From 2 to 300 K, the increases gradually, and it can be evaluated as a linear function of temperature above 300 K as follows:This result is expected to be useful as basic thermodynamic data of Mg-based alloys. 相似文献
4.
The transition phase of MgTe from rock salt structure (B1) to cesium chloride structure (B2) is investigated by ab initio plane-wave pseudopotential density functional theory method. The thermodynamic properties of the B1 and B2 structures are obtained through the quasi-harmonic Debye model. Our results indicated that MgTe undergoes a structural phase transition from B1 to B2 at about 90.32 GPa. The dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and heat capacity CV on the pressure P, the Grüneisen parameter ratio (γ − γ0)/γ0 on pressure P, the bulk moduli ratio (B − B0)/B0 on pressure P, as well as the heat capacity CV on the temperature T are estimated. 相似文献
5.
Manjulata Sahu K. Krishnan M.K. Saxena K.L. Ramakumar 《Journal of Alloys and Compounds》2009,482(1-2):141-146
Gd6UO12(s) was synthesized by citrate–nitrate combustion method. Thermal expansion measurements of this compound were carried out in the temperature range of 298–1273 K by high temperature X-ray powder diffractometry and compared with other rare earth compounds of similar stoichiometry reported in literature. Heat capacity of Gd6UO12(s) was also measured by differential scanning calorimetry in the temperature range of 330–720 K. Enthalpy, entropy and free energy functions for Gd6UO12(s) were computed. 相似文献
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7.
V. Anbarasan B. Jeya Ganesh S. Raju S. Murugesan E. Mohandas U. Kamachi Mudali Geetha Manivasagam 《Journal of Alloys and Compounds》2008,463(1-2):160-167
The thermal properties of Ti–4 wt.%Nb–4 wt.%Zr alloy, namely the enthalpy increment and heat capacity have been characterized as a function of temperature using drop and differential scanning calorimetry, respectively. The measured data clearly attested to the presence of a phase change from α (hcp) to β (bcc) phase at about 1100 ± 5 K. In fact, the alloy exhibited a transformation domain in the temperature interval 1100–1170 K. The enthalpy associated with the α → β phase change is estimated to be about 73 (±5%) J g−1. The jump in the specific heat at the transformation temperature is 1714 (±7%) J kg−1 K−1. The drop and differential scanning calorimetry results are consolidated to obtain the first experimental data on the thermodynamic quantities of this alloy. 相似文献
8.
M. T. Clavaguera-Mora 《Journal of Alloys and Compounds》1995,220(1-2):197-205
Modern technology makes it possible to obtain different kinds of glassy material. In the as-prepared state most of these show relaxation effects, glass transition and crystallization under heat treatment, with very similar phenomenological peculiarities. The thermodynamic treatment of glassy materials is complicated by the fact that the glassy state is not always a metastable state but is sometimes an unstable state. Evaluation of the entropy of the glass, with respect to the corresponding stable crystalline phase at the same temperature and pressure, from heat capacity measurements is discussed. The “ideal glass” concept is introduced to calculate the Gibbs free energy of formation of the glass. The residual entropy is presented as a measure of the glass deviation from ideal behaviour. The treatment is extended to alloy glass. The thermodynamic and kinetic parameters which control the crystallization process are reviewed. Polymorphous and primary crystallization are considered, assuming, either homogeneous or inhomogeneous nucleation, followed by interface-controlled crystal growth. 相似文献
9.
《Intermetallics》2014
We employ density functional theory (DFT) to calculate pressure dependences of selected thermodynamic, structural and elastic properties as well as electronic structure characteristics of equiatomic B2 FeTi. We predict ground-state single-crystalline Young's modulus and its two-dimensional counterpart, the area modulus, together with homogenized polycrystalline elastic parameters. Regarding the electronic structure of FeTi, we analyze the band structure and electronic density of states. Employing (i) an analytical dynamical matrix parametrized in terms of elastic constants and lattice parameters in combination with (ii) the quasiharmonic approximation we then obtained free energies, the thermal expansion coefficient, heat capacities at constant pressure and volume, as well as isothermal bulk moduli at finite temperatures. Experimental measurements of thermal expansion coefficient complement our theoretical investigation and confirm our theoretical predictions. It is worth mentioning that, as often detected in other intermetallics, some materials properties of FeTi strongly differ from the average of the corresponding values found in elemental Fe and Ti. These findings can have important implications for future materials design of new intermetallic materials. 相似文献
10.
11.
First principles calculation and quasi-harmonic Debye model were used to obtain more physical properties of zirconium carbide under high temperature and high pressure. The results show that the B1 structure of ZrC is energetically more favorable with lower heat of formation than the B2 structure, and that mechanical instability and positive heat of formation induce the inexistence of the B2 structure at normal pressure. It is also found that the B1 structure would transform to the B2 structure under high pressure below the critical point of V/V0=0.570. In addition, various thermodynamic and elastic properties of ZrC are obtained within the temperature range of 0–3000 K and the pressure range of 0–100 GPa. The calculated results not only are discussed and understood in terms of electronic structures, but also agree well with corresponding experimental data in the literature. 相似文献
12.
First-principles calculations of lattice dynamics and thermodynamic properties of orthorhombic LiInS2 and LiInSe2 and chalcopyrite LiInTe2 have been performed within density functional perturbation theory using norm conserving pseudopotentials. Theoretical values of phonon mode frequencies are in good agreement with the experimental data available for these crystals obtained by methods of Raman spectroscopy and infrared one. In the whole frequency range a significant decrease of the vibrational frequencies is observed going from LiInS2 to LiInSe2 and LiInTe2, which is a consequence of the anion radius increase. The lattice vibrations of In-X (X = S, Se, Te) bonds are mainly located in the low-frequency and mid-frequency ranges, and the Li-X bond vibrations are dominated in the higher frequency range. The mixed covalent-ionic nature of the three compounds is manifested by Born effective charge data. The vibration patterns of orthorhombic LiInS2 and chalcopyrite LiInTe2 were discussed in detail. The temperature dependences of thermodynamic quantities (including the internal energy, free energy, heat capacity, entropy and the Debye temperature ΘD) of all the three compounds were also presented in this paper. It is proved that Debye stiffness increases from LiInTe2 to LiInSe2 and LiInS2. 相似文献
13.
Masashi Sato R.V. Denys A.B. Riabov V.A. Yartys 《Journal of Alloys and Compounds》2005,400(1-2):184-187
The Pressure–Composition–Temperature (P–C–T) relations for the LaNiIn, LaNi0.95Cu0.05In and LaNiIn0.98Al0.02–H systems were measured by a volumetric Sieverts’ method at 398–423 K. All isotherms show plateau pressure regions indicating equilibria between two hydride phases. The replacements of Ni by Cu and In by Al affect the P–C–T diagrams, stability of the hydrides, homogeneity regions of the hydrides formed, slope of the isotherms and critical temperatures of the β–γ transition. In addition, the Cu-doping induces a significant hysteresis between the hydrogen absorption and desorption processes. The relative partial molar thermodynamic properties for the studied systems are: ΔHH = −34.6 ± 2.1 kJ (molH)−1, ΔSH = −70.7 ± 3.6 J (K·molH)−1 for LaNiIn–H; ΔHH = −34.1 ± 0.5 kJ (molH)−1, ΔSH = −74.9 ± 1.0 J (K·molH)−1 for LaNi0.95Cu0.05In–H; ΔHH = −33.2 ± 0.8 kJ (molH)−1, ΔSH = −68.3 ± 1.2 J(K·molH)−1 for LaNiIn0.98Al0.02–H. 相似文献
14.
Temperatures and enthalpies of phase transitions of 17 lanthanide(III) halides determined experimentally are reported. Correlations were made between temperature of fusion of lanthanide(III) halides, on the one hand, and enthalpy of fusion, on the other, versus atomic number of lanthanide. According to this classification, the lanthanide(III) halides split into groups, as also do the corresponding crystal structures. A correlation between the crystal structure of lanthanide(III) halides and their respective entropy of fusion (or entropy of fusion + entropy of solid–solid phase transition) was inferred from the aforementioned features. Fusion in those halides with hexagonal, UCl3-type and orthorhombic, PuBr3-type, structures entails an entropy of fusion change (or entropy of fusion + entropy of solid–solid phase transition change) by 50 ± 4 J mol−1 K−1. The homologous entropy change within the group of halides having the rhomboedric, FeCl3-type, structure, is smaller and equals 40 ± 4 J mol−1 K−1. Halides with monoclinic, AlCl3-type, crystal structure constitute a third group associated to an even smaller entropy change upon fusion, only 31 ± 4 J mol−1 K−1. The halides with lower entropies of fusion also have a lower S1300 K − S298 K indicating either a higher degree of order in the liquid or a higher entropy in the solid at room temperatures. 相似文献
15.
Ziya S. AlievGulnara I. Ibadova Jean-Claude TedenacAndrei V. Shevelkov Mahammad B. Babanly 《Journal of Alloys and Compounds》2011,509(24):6773-6776
The solubility of YbTe in Sb2Te3 is investigated by a combination of DTA, XRD, SEM, and EMF methods. The fragment of the T-x phase diagram of the YbTe-Sb2Te3 system is constructed for 0-25 mol.% YbTe. It is shown that the solubility limit for YbTe in Sb2Te3 is achieved at 15 mol.% YbTe at 300 K and at 17.5 mol.% YbTe at 855 K. From the EMF measurements with an YbTe electrode the partial thermodynamic functions of the YbTe pseudo-component are calculated for the alloys of different compositions. Also, the standard integral thermodynamic functions of the YbTe dissolution in Sb2Te3 as well as the standard thermodynamic functions of formation and the standard entropy of the solid solution are calculated from the experimental data. 相似文献
16.
《Intermetallics》2015
The structural and elastic properties of the L12 structure Ir3Nb and Ir3V under pressure have been investigated by means of the first principles calculations based on the density functional theory within the generalized gradient approximation. The lattice parameters of Ir3Nb and Ir3V obtained by minimization of the total energy are consistent with the available experimental and other theoretical results. In addition, the elastic constants (C11, C12, C44) of Ir3Nb and Ir3V show that they are mechanical stable structures under pressure. The values of B/G exhibit an upward trend with increasing pressure, which means its ductility increased. When the pressure reaches 45 GPa, the Cauchy pressures and B/G values reveal that Ir3Nb and Ir3V change from brittle to ductile. Finally, through quasi-harmonic Debye model, the temperature and pressure dependences of thermodynamic properties are predicted in a wide pressure (0–50 GPa) and temperature (0–1200 K) ranges. 相似文献
17.
The site preference of Fe in Cr23−xFexC6 is investigated based on the interatomic potentials obtained by the lattice inversion method. The calculated results show that Fe atoms preferentially substitute for Cr at 4a sites first and then 8c sites. The structural parameters of Cr23−xFexC6 with content x are calculated and the results are consistent with experimental results. The calculated cohesive energies indicate that the increase in x value is accompanied by the decrease in the stability of Cr23−xFexC6. The thermodynamic properties of Cr23C6, such as the phonon density of states and vibrational entropy, as well as the bulk modulus of Cr23−xFexC6 are evaluated. The calculated results are in good agreement with experimental results. This work provides a simple and promising method for studying the properties of carbides with complex structures. 相似文献
18.
采用基于密度泛函理论的第一性原理计算方法,系统研究高压高温下Re2N的晶体参数、力学性能和热力学性能。结果表明:在高压下Re2N具有明显的弹性各向异性,与弹性常数C12、C13、C44相比,C11和C33的变化随着压力的变化非常明显。此外,首次计算Re2N的体弹模量B、弹性模量E和剪切模量G沿不同晶轴的分布。弹性模量在一些主要晶轴方向上的大小分布趋势如下:[0001][1211][1010][1011]EEEE〉〉〉。计算结果还表明:在(0001)晶面,Re2N的抗剪切能力是最低的,从而极大地减小对大剪切变形的阻力。基于准简谐德拜模型,在0~50GPa压力和0~1600K温度下得到德拜温度、格林艾森参数、热传导以及热扩散系数的变化行为。 相似文献
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20.
《Intermetallics》2016
First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co3(Al,Mo,Nb) with the L12 structure. Calculated elastic constants show that Co3(Al,Mo,Nb) is mechanically stable and possesses intrinsic ductility. It is found that the shear and Young's moduli of Co3(Al,Mo,Nb) are smaller than those of Co3(Al,W). Calculated density of states indicate the existence of covalent-like bonding in Co3(Al,Mo,Nb). Temperature-dependent thermodynamic properties of Co3(Al,Mo,Nb) can be described satisfactorily using the Debye-Grüneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data can be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys. 相似文献