第一性原理研究Pt-Zr系统中化合物的生成焓/体模量与原子体积的线性相关性

通过第一性原理的计算方法,研究118种不同结构的Pt-Zr中间化合物,并选取相关的物理性能,如结构稳定性、晶格常数、生成焓、弹性常数以及体模量等进行计算。根据计算得出的生成焓信息,绘制Pt-Zr系统的基态能量曲线。计算得到的物理相关信息为未来的热力学计算和原子尺度模拟提供基础数据。在选取的 Pt-Zr化合物中,存在两组线性相关关系：生成焓与原子体积成正线性相关,而体模量与原子体积成负线性相关关系。     

First principles calculations of the stability of the T2 and D88 phases in the V–Si–B system

The crystal and electronic structures of D8_l-V₅SiB₂ and D8₈-V₅Si₃B ternary compounds have been investigated by means of first principle calculations. The calculated structural parameters are in very good agreement with the experimental data. The calculated values of the enthalpies of formation at T = 0 K of the D8_l-V₅SiB₂ and D8₈-V₅Si₃B ternary compounds are −67.1 and −62.1 kJ/mol of atoms respectively. The total and partial electronic densities of states show a strong hybridization between the B p states and V d states. The defect enthalpies of formation as well as the mixing enthalpies have been computed. These data are essential for the modeling of the D8_l and D8₈ phases in the V–Si–B ternary system. A partial V–VSi₂–VB isothermal section at 298 K is proposed.     

Revision of the enthalpies and gibbs energies of formation of calcium oxide and magnesium oxide

Major revisions in the enthalpies and Gibbs energies of formation of calcium oxide and magnesium oxide are presented. In free-evaporation experiments over the temperature range of 1830 to 2070 K, the kinetics of vaporization of calcium oxide and magnesium oxide have been studied. Conditions of local equilibrium were established. The results lead to new values for the standard enthalpies of formation of CaO and MgO. The Δ_fH₂₉₈ ⁰ of CaO is ≈33 kJ/mol more positive than the currently tabulated value, whereas that for MgO is ≈34 kJ/mol more negative. The currently tabulated values could not account for these observations nor for other recent studies. These significant changes result in a reversal of the relative thermodynamic stabilities of CaO and MgO, with MgO now indicated as the more stable oxide at lower temperatures on Ellingham diagrams. These results are consistent with recent work on the formation of CaC₂, solubility product measurements in liquid iron, and with theoretical models based on ionic radii.     

Revision of the enthalpies and gibbs energies of formation of calcium oxide and magnesium oxide

Major revisions in the enthalpies and Gibbs energies of formation of calcium oxide and magnesium oxide are presented. In free-evaporation experiments over the temperature range of 1830 to 2070 K, the kinetics of vaporization of calcium oxide and magnesium oxide have been studied. Conditions of local equilibrium were established. The results lead to new values for the standard enthalpies of formation of CaO and MgO. The Δ_fH₂₉₈ ⁰ of CaO is ≈33 kJ/mol more positive than the currently tabulated value, whereas that for MgO is ≈34 kJ/mol more negative. The currently tabulated values could not account for these observations nor for other recent studies. These significant changes result in a reversal of the relative thermodynamic stabilities of CaO and MgO, with MgO now indicated as the more stable oxide at lower temperatures on Ellingham diagrams. These results are consistent with recent work on the formation of CaC₂, solubility product measurements in liquid iron, and with theoretical models based on ionic radii.     

Standard enthalpies of formation of some 3d transition metal gallides by high temperature direct synthesis calorimetry

The standard enthalpies of formation of some 3d transition metal gallides have been measured by high temperature direct synthesis calorimetry at 1373±2 K. The following results in kJ/mol of atoms are reported: Sc₅Ga₃ (−59.4±2.0); Ti₂Ga (−39.0±1.4); V₂Ga₅ (−16.6±1.7); Cr₃Ga (−11.8±1.8); FeGa₃ (−24.8±2.1); CoGa₃ (−29.4±2.2) and NiGa (−44.9±1.9). The results are compared with some earlier values obtained by solution calorimetry or derived from EMF measurements. They are also compared with predicted values from the semi-empirical model of de Boer et al. and with available enthalpies of formation for 3d transition metal aluminides and germanides.     

Molar enthalpies of formation of BaCmO3 and BaCfO3

The enthalpies of solution of BaCmO₃ and BaCfO₃ in 1.00 mol dm⁻³ HClO₄ were measured at 298.15 ± 0.05 K and p° = 101.325 kPa as −(345.3±4.7) and −(347.2 ± 1.9) kJ mol⁻¹, respectively. The resulting standard molar enthalpies of formation, Δ_fH_m°(BaCmO₃, cr) = −(1517.8 ± 7.1) kJ mol⁻¹ and Δ_fH_m°(BaCfO₃, cr) = −(1477.9 ± 5.6) kJ mol⁻¹, together with other corresponding experimental values for several lanthanide, actinide and transition metal complex oxides with barium and strontium, are used to estimate the molar enthalpies of formation of a number of homologous actinide compounds. The present results also provide additional information on the standard molar enthalpy of formation of CfO₂ and on the Cf⁴⁺/Cf³⁺ standard potential.     

Theoretical calculation of the mixing enthalpies of 21 IIIB-IVB, IIIB-VB and IVB-VB binary alloy systems

The calculation of the formation/mixing enthalpies of binary alloys is an important problem. There have been no systematic theoretical calculations of the mixing enthalpies for group B alloy systems using the famous Miedema theory or from the theoretical methods of first principle. Therefore such calculations for the 21 binary group IIIB-IVB, IIIB-VB and IVB-VB metal alloy systems are performed systematically for the first time using a subregular model. The results show that the agreement between the calculations and experimental data is pretty good and could be accepted from the theoretical or experimental points of view. From the present results and those in other two papers by the authors, it also can be concluded that the subregular model can be used for calculating the mixing enthalpies for all the 36 alloy systems combined with the 9 group B metals of Zn, Cd, Ga, In, Tl, Sn, Pb, Sb and Bi.     

Chemical and thermodynamic properties of several Al–Ni–R systems

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.     

采用钛钢热轧复合带的防蚀法

运用Ｍｉｅｄｅｍａ理论系统地研究了镁与稀土镧系元素构成的二元合金的热力学性质，计算了其液态混合焓和固态金属间化合物的形成焓，计算的结果同已有的实验结果和理论预言的结果符合得比较好。     

Enthalpies of formation of magnesium compounds from first-principles calculations

An energetics database of binary magnesium compounds has been developed from first-principles calculations. The systems investigated include Mg–X (X = As, Ba, Ca, Cd, Cu, Dy, Ga, Ge, La, Lu, Ni, Pb, Sb, Si, Sn and Y). The calculated lattice parameters and enthalpies of formation of binary compounds in these systems are compared with both experimental data and thermodynamic databases.     

Thermodynamic Optimization of the Ni-Al-Ce Ternary System

The Ni-Al-Ce ternary system has been thermodynamically optimized in order to be integrated into the database for Ni-base alloys containing rare earth elements. A comprehensive set of thermodynamic parameters including all the ternary intermetallic compounds have been obtained. The calculated enthalpies of formation for ternary compounds by the present work are consistent with values from other sources. Isothermal sections at 1073 and 773 K and liquidus projection have been calculated. Ternary phase equilibria have been well reproduced compared to experimental data.     

Prediction of the formation enthalpies of Bi–Cd–Ga–In–Pb–Sn–Zn liquid alloys by binary infinitely dilute enthalpies

The molecular interaction volume model (MIVM) is used to predict the formation enthalpies of Bi–Cd–Ga–In–Sn–Zn and Bi–Cd–Ga–In–Pb–Sn–Zn liquid alloys, using only the infinitely dilute enthalpies of binary systems and the coordination numbers of the constituent elements in liquid alloys. In addition, the infinitely dilute enthalpies of binary system were obtained by Miedema's theory without requiring experimental data. The results are compared with the experimental data and calculated values using the Hoch–Arpshofen model (HAM), the results indicate that the model is reliable as well as being convenient.     

Enthalpies of formation of compounds in Al-Ni-Y system

The enthalpies of formation of the ternary compounds Al4NiY, Al2NiY, Al2Ni6Y3, Al16 Ni3Y, AlNiY, Al3Ni2Y, AlNi8Y3, Al7Ni3Y2, and of the binary comp ounds Al2Y containing nickel and Ni5Y containing aluminum have been determined by high temperature reaction calorimetry. The enthalpy values measured are compared to previously published results where available as well as extended Miedema model predictions. The melting points of the compounds were determined by DTA and X-ray diffraction was used to confirm the crystal structures of the compounds. The enthalpi es of formation of the ternary compounds show a maximum along the 50%Al (mole fr action) section. The ternary compounds appear along lines of constant yttrium content consistent with binary compound solubility extensions.     

Standard enthalpies of formation of some carbides, silicides and germanides of cerium and praseodymium

The standard enthalpies of formation of some congruent-melting compounds in the binary systems Re---X, where Re Ce, Pr or La and X C, Si or Ge have been determined by direct-synthesis calorimetry at 1473 ± 2 K. The following values of ΔH_f^o are reported: CeC₂, −25.4 ± 1.4 kJ (mol atom)⁻¹; CeSi₂, −60.5 ± 2.0 kJ (mol atom)⁻¹; CeSi, −71.1 ± 3.3 kJ (mol atom)⁻¹; Ce₅Ge₃, −73.4 ± 2.3 kJ (mol atom)⁻¹; CeGe_1.6, −75.6 ± 1.9 kJ (mol atom)⁻¹; PrC₂, −29.4 ± 1.6 kJ (mol atom)⁻¹; PrSi₂, −61.5 ± 1.7 kJ (mol atom)⁻¹; PrSi, −78.1 ± 1.9 kJ (mol atom)⁻¹; Pr₅Ge₃, −70.4 ± 2.3 kJ (mol atom)⁻¹; PrGe_1.6, −81.7 ± 1.7 kJ (mol atom)⁻¹; LaSi₂, −56.8 ± 2.5 kJ (mol atom)⁻¹. The results are compared with earlier experimental data, with predicted values from Miedema's semiempirical model, and with available data obtained for Sn and Pb compounds by Borzone et al., by Palenzona and by Palenzona and Cirafici.     

High temperature calorimetry: recent developments

In the last 10 years, high temperature calorimetry has allowed a considerable increase in the knowledge of the thermochemistry of metallic systems: determinations of enthalpies of formation of intermetallic compounds or of solid solutions, and of enthalpies of mixing in liquid alloys. The recent extension of the domains of applicability of high temperature calorimetry has been achieved by the development of calorimeters working at increasingly high temperature with very acceptable precision. It must also be pointed out that new methods have been developed for cases where the classical methods failed to obtain reliable results. The purpose of this paper is to emphasize the results obtained recently in systems where the lack of reliable thermochemical information leaves much to be desired.     

Structural and mechanical properties of Fe–Al compounds: An atomistic study by EAM simulation

The structural properties, formation enthalpies, and mechanical properties of Fe–Al compounds (FeAl, Fe₂Al, Fe₃Al, FeAl₂, FeAl₃ and Fe₂Al₅) are studied by using embedded-atom method (EAM) which is acquired by Mobius lattice inversion. The potential is transferrable and therefore does well for studying different Fe–Al compounds. The calculated lattice parameters and cohesive energies of Fe–Al compounds agree with the experimental and some EAM results. According to elastic constants restrictions, all the six Fe–Al compounds are mechanically stable. The calculated bulk moduli of the compounds increase with the increasing Fe concentration. Furthermore, results showed that FeAl, Fe₃Al, FeAl₃, FeAl₂, Fe₂Al₅ have lower ratios of shear modulus to bulk modulus and Fe₂Al has higher ratio.     

Thermodynamic optimization of the Cu-Nd system

The thermodynamic constraints to eliminate artificial phase relations were introduced with the Cu-Nd system as an example. The enthalpies of formation of the compounds Cu₆Nd, Cu₅Nd, Cu₂Nd and αCuNd are calculated using density functional theory. Taking into account all the experimental data and the first-principles calculated enthalpies of formation of these compounds, the thermodynamic optimization of the Cu-Nd system was performed under the proposed thermodynamic constraints. It is demonstrated that the thermodynamic constraints are critical to obtain a set of thermodynamic parameters for the Cu-Nd system, which can avoid the appearance of all the artificial phase relations.     

Application of reaction calorimetry to metallic systems

The application of reaction calorimetry to metallic systems is examined. Different commonly used procedures and their respective fields of application are described: (a) direct and indirect drop method with flow calorimeters, (b) solid-solid reaction calorimetry (Kleppa's and Gachon's methods), (c) dissolution calorimetry in metallic baths, and (d) precipitation calorimetry. Some examples of results on binary and ternary alloys are given as illustrations: (a) the determination of the enthalpies of formation of metallic melts with respect to concentration and temperature, (b) the measurements of the enthalpy of formation of solid compounds, and (c) the determination of phase boundaries from isothermal reaction calorimetry.     

Structural stability of some CsCl structure HfTM (TM = Co, Rh, Ru, Fe) compounds

In order to investigate Hf-TM (TM = Fe, Co, Rh, Ru) phase diagrams in the region of 50:50% atomic ratio, we performed ab initio Full-Potential Linearized Augmented Plane Waves calculations of the most stable Hf and TM elemental phases and HfTM compounds of the CsCl and CuAu structure types. The obtained electronic structures, cohesive energies and enthalpies of formation are discussed and compared to some of the existing models and available experimental data. The non-existing compound HfFe is found to be at least metastable, and the reason for its absence from the phase diagram is discussed.     

Enthalpies of formation of Ni3Al: Experiment versus theory

Using Al solution calorimetry, enthalpies of formation of Ni₃Al in the L1₂ structure ranging from-41.3 to -42.3 kJ/mol were determined at temperatures from 300 to 1123 K. These enthalpies are substantial for an intermetallic compound and display a slight temperature dependence, which is contained within the experimental error. This temperature dependence is related to the lack of any transformations of the compound, which remains ordered up to the melting temperature. The measured enthalpies were combined with other thermodynamic data to estimate the excess entropy of formation of Ni₃Al. The high degree of ordering in the compound is reflected in the large negative value of the excess entropy,whose absolute value exceeds those for other high melting temperature intermetallic compounds. The full-potential linearized augmented Slater-type orbital method (FLASTO) was used to calculate the enthalpies of formation of paramagnetic and ferromagnetic Ni ₃ Al. These enthalpies of formation indicate the compound to be a weak ferromagnet, and they are in good agreement with the calorimetric data.