High Temperature Thermodynamic Data for CdTe(c)

The high temperature heat capacity, Gibbs energy of formation, and standard enthalpy and entropy of formation at 298 K are combined with thermodynamic data for Cd and revised data for Te to provide an internally consistent data set for CdTe(c). Equations are given for the Gibbs energy of formation from Cd(g) and Te₂(g) and from the solid or liquid elements as a function of temperature. These give values similar to those used before. However, the derived enthalpy and entropy of formation are significantly different due to a revised heat capacity for CdTe(c). The standard enthalpy and entropy of formation at 298.15 K from the gases are −293262 J/mol and −200.593 J/mol K, respectively. From the solid elements they are −100270 and −4.5334.     

Thermodynamic Properties of YbRhO<Subscript>3</Subscript> and Phase Relations in the System Yb-Rh-O

Thermodynamic properties of the ternary oxide YbRhO₃ were determined by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the solid electrolyte in the temperature range from 900 to 1300 K. The standard Gibbs energy of formation of YbRhO₃ from component binary oxides Yb₂O₃ with C-rare earth type structure and Rh₂O₃ with orthorhombic structure can be represented by the equation,

$$\Delta_{\text{f(ox)}} G^{\text{o}} ( \pm 130)/{\text{J/mol}} = - 43164 + 3.436\,({\text{T/K}}).$$

Standard enthalpy of formation of YbRhO₃ from elements in their normal standard states is ?1153.18(±3) kJ/mol and its standard entropy is 100.93(±0.6) J/K/mol at 298.15 K. The decomposition temperature of YbRhO₃ is 1671(±3) K in pure oxygen, 1566(±3) K in air and 1047(±3) K at an oxygen partial pressure of \(\left( {P_{{{\text{O}}_{2} }} /{\text{P}}^{\text{o}} } \right) = 10^{ - 6}\), where P^o = 0.1 MPa is the standard pressure. Decomposition temperature was confirmed by DTA/TGA. Phase diagrams for the system Yb-Rh-O are computed using the thermodynamic data.

     

Determination of thermodynamic properties in full composition range of Ti-Al binary melts based on atom and molecule coexistence theory

The results of predicting thermodynamic properties in the full composition range of Ti-Al binary melts in a temperature range from 1973 to 2273 K were obtained by coupling with the developed thermodynamic model for calculating mass action concentration N_i of structural units in Ti-Al system based on the atom and molecule coexistence theory (AMCT). Temperature dependence of the activity coefficients of Ti and Al in natural logarithmic form in the infinitely dilute solution (0>x_Ti<0.01) of Ti-Al binary melts was also determined from the calculated activity coefficients of Ti and Al at temperatures of 1973, 2073, 2173, and 2273 K. The standard molar Gibbs free energy change of dissolving pure liquid element i(l) for forming 1% (mass fraction) element i in Ti-Al binary melts further was deduced. With the aid of this model, meanwhile, the determined excess thermodynamic properties, such as the excess molar mixing Gibbs free energy/entropy/enthalpy were also calculated.     

Phase Equilibria in the System Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-CoO and Gibbs Energy of Formation of Ca<Subscript>3</Subscript>CoAl<Subscript>4</Subscript>O<Subscript>10</Subscript>

An isothermal section of the system Al₂O₃-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca₃CoAl₄O₁₀, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca₃CoAl₄O₁₀ in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: From the emf of the cell, the standard Gibbs energy change for the Ca₃CoAl₄O₁₀ formation reaction, CoO + 3/5CaAl₂O₄ + 1/5Ca₁₂Al₁₄O₃₃ → Ca₃CoAl₄O₁₀, is obtained as a function of temperature: /J mol⁻¹ (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca₃CoAl₄O₁₀ from its component binary oxides, Al₂O₃, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca₃CoAl₄O₁₀ at 298.15 K are evaluated. Chemical potential diagrams for the system Al₂O₃-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.     

Co_6W_6C化合物的热力学研究

以高纯钨、钴、碳粉为原料,在真空条件下制备获得物相纯净的Co_6W_6C化合物,对Co_6W_6C进行系列实验测定并结合计算得出了其相关的热力学参数。结果表明:在原料粉中碳含量为0.98%~1.06%(质量分数)、真空反应温度为1000℃、保温时间为1 h的条件下,可制备获得物相纯净的Co_6W_6C。结合其等压热容及1173 K下氧化反应的反应焓测定结果,通过计算获得了Co_6W_6C的标准摩尔熵(S_m~Θ)、标准摩尔生成焓(Δ_fH_m~Θ)等热力学参数以及其等压热容(C_p)、焓(H)、熵(S)和吉布斯自由能(G)等基础热力学参量随温度变化的函数关系。     

Sintering characteristics and microstructure of WC-Co-VC/Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> ultrafine cemented carbides

The sintering characteristics, microstructure, and mechanical properties of ultrafine WC-12%Co-0.2%VC/0.5%Cr₃C₂ cemented carbides were investigated. Dilatometric and differential thermal analyses (DTA) indicate that the compacts start to shrink at 600°C, the shrinkage rate peak is at 1190°C, and the liquid formation temperature is lower than the W-C-Co eutectic temperature (1330°C). Microstructure analysis results show that the cemented carbides with fine and homogeneous microstructure were obtained when sintered at 1430°C. Continuous and discontinuous grain growth was suppressed due to the synergistic action of VC/Cr₃C₂. The transverse rupture strength (TRS) of the samples reaches 4286 MPa, with the hardness HRA 92.1. The fine and homogeneous microstructure, alloy strengthening, and different phase constitutions of binder in the cemented carbides result in high hardness and TRS. Continuous and discontinuous grain growth was observed in the cemented carbide sintered at 1450°C, which results in significant decreases of hardness and TRS. It indicates that VC/Cr₃C₂ additions in the cemented carbides can only suppress the grain growth at a certain temperature.     

第一性原理研究Re的热力学性质

基于准谐Debye-Grüneisen模型,运用第一性原理缀加投影平面波方法研究了Re的热力学性质,拟合了Re的状态方程,计算了Re不同压强下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化关系。结果表明:采用八阶Birch-Murnaghan方程拟合得到的Re压强-体积曲线与实验测量结果吻合较好;计算的零压下吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化均与实验值符合较好;在零压,50、100、150和200GPa压强下,Re的弹性模量和吉布斯自由能随温度升高而减小;焓、熵随温度升高而增加;Re的电子等容热容随温度线性增加,晶格振动等容热容在低温下符合3T幂次规律并随温度增加而迅速增大,且在高温时逐渐接近Dulong-Petit极限;预测的德拜温度约为430K,与实验结果一致。     

The structural effect of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on their thermodynamic characteristics of adsorption from aqueous organic solutions on phenyl-bonded silica gel

The thermodynamic characteristics of adsorption of substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from aqueous organic solutions on phenyl-bonded silica gel were determined in the Henry region via the method of high-performance liquid chromatography. The influence of the structure of the studied compounds on their thermodynamic characteristics of adsorption from binary aqueous organic solvents of different natures was examined. The correlation dependences of the standard differential molar changes in the Gibbs energy, enthalpy, and entropy of adsorption on the van der Waals surface area and reduced dipole moment of molecules of the examined compounds were found. The main factors in optimization of the separation techniques and adjustment of the adsorption selectivity of phenyl-bonded silica gel were determined under conditions of reversed-phase high-performance liquid chromatography.     

Thermodynamic Evaluation of Yttrium

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Thermodynamics of La based La–Al–Cu–Ni–Co alloys studied by temperature modulated DSC

The onset and offset melting temperatures T_m and T_l, glass transition temperature T_g and heat of fusion ΔH_m of six La based La–Al–Cu–Ni–(Co) alloys were measured by DTA or DSC at a heating rate of 20 K/s. The absolute values of specific heat capacity for the undercooled liquid and the corresponding crystalline of these six alloys were obtained by means of temperature-modulated DSC (TMDSC). Entropy, enthalpy and Gibbs free energy differences between the undercooled liquid and crystalline of these alloys as a function of temperature have been calculated. Their glass forming ability was discussed from a thermodynamic point of view.     

High Temperature Thermodynamic Properties of ZnTe(s)

We have gathered the partial pressure, Knudsen cell, and emf measurements on ZnTe(s) from which the Gibbs energy of formation can be calculated. Published partial pressures of diatomic tellurium have been adjusted to take account of a subsequently published third law analysis of tellurium. The equation used to calculate the total pressure from the rate of mass loss from an extensive set of Knudsen cell measurements has been corrected to give a 5% increase in total pressure and the Gibbs energy of formation has been recalculated. A high temperature heat capacity for ZnTe(s) has been selected from the published data. The Gibbs energies of formation as a function of temperature have then been fit using a third law analysis to give two essentially equally good but extreme fits. In the first, the standard enthalpy of formation agrees with the calorimetric value of −119 kJ/mol but the standard entropy of ZnTe(s) is low by 2-3 J/mol K. In the second, the standard enthalpy of formation is more positive than the calorimetric values by about 3 kJ/mol but the standard entropy of ZnTe(s) is 82 J/mol K and close to the value from low temperature heat capacity measurements. We select values of −119.49 kJ/mol for the standard enthalpy of formation and 78.23 J/mol K for the standard entropy.     

Free energy of crystal–liquid interface

It is demonstrated that a simple model, free of any adjustable parameter, can be developed to predict the free energy of a crystal–liquid interface σ_sl based on the Gibbs–Thomson equation and a model for the size-dependent melting temperature. This model has improved Turnbull's empirical equation. In the model, σ_sl depends on not only the melting enthalpy of crystals, but also the vibrational component of the overall melting entropy of the crystals. The predicted values of σ_sl for different types of crystals, such as true metals, meta metals, semiconductors, ionic crystals and organic crystals, are confirmed by available experimental results in the experimental error range.     

Synthesis of Ti3AlC2 by SHS and thermodynamic calculation based on first principles

In this paper, a self-propagating high-temperature combustion synthesis with the pseudo-hot isostatic pressing process(SHS/PHIP) was employed to fabricate high-pure Ti3AlC2(U 240 mm). In addition, the first principle with quasi-harmonic approximation was applied for the thermodynamic properties’ investigation of Ti2AlC and Ti3AlC2, including Gibbs free energy, enthalpy, and entropy.With temperature increasing, Gibbs free energy increases,but enthalpy and entropy decrease. The present work provides the theoretical proof for the synthesis mechanism of Ti3AlC2 by SHS/PHIP.     

Thermodynamic Evaluation of Gadolinium

ＴｈｅｒｍｏｄｙｎａｍｉｃＥｖａｌｕａｔｉｏｎｏｆＧａｄｏｌｉｎｉｕｍＳｈｅｎＨｕａｓｅｎ，ＺｈａｎｇＷｅｉｊｉｎｇ，ＬｉｕＧｕｏｑｕａｎ，ＷａｎｇＲｕｎａｎｄＤｕＺｈｅｎｍｉｎ（沈化森）（张维敬）（刘国权）（王润）（杜振民）（Ｄｅｐａｒｔｍｅｎｔｏ...     

Formation and morphology of M<Subscript>7</Subscript>C<Subscript>3</Subscript> in low Cr white iron alloyed with Mn and Cu

The presence of M₇C₃ carbide in white iron enhances its wear resistance because of high hardness. Scanning electron microscopy (SEM) revealed its morphology as a pencil-like hexagonal structure. On the basis of the SEM observations, elemental distribution studies, and differential thermal analysis (DTA) of some heat-treated hypoeutectic white irons alloyed with Cr, Mn, and Cu, it is concluded that M₇C₃ carbides form as a result of attainment of a favorable condition in the liquid phase present at the austenite grain boundaries. Segregation of phosphorus in the intercellular regions and formation of a copper-rich intermetallic is responsible for the formation of this liquid phase. Austenite was found to nucleate first, followed by the nucleation and growth of M₇C₃ carbide in its vicinity, because of rejection of C and Cr during formation of austenite. The rosette structure generally observed is formed from the joining of M₇C₃ carbides by precipitation of secondary carbides.     

On the temperature behavior of a tensoresistive effect in the amorphous Fe<Subscript>80</Subscript>B<Subscript>14</Subscript> alloy

Investigation of the temperature behavior of the coefficient of tensoresistance π of the amorphous Fe₈₆B₁₄ alloy in a temperature range from room temperature to the crystallization temperature has been carried out. It has been revealed that below the Curie temperature T _C, in the interval of existence of elinvar properties, π in this alloy increases only weakly, with a temperature coefficient of 4 × 10^?4 K^?1. At T > T _C, a stronger temperature increase of π is observed. An analysis performed has shown that the most probable reason of the observed temperature changes in π was a temperature-induced change in Young’s modulus of the alloy. It has been shown that during crystallization the coefficient of tensoresistance π decreases with increasing amount of crystalline phases in the alloy.     

Thermodynamic optimization of the AgCl-KCl and BaCl<Subscript>2</Subscript>-LiCl systems

The values of the thermodynamic properties of the liquid phase of the AgCl-KCl and BaCl₂-LiCl systems were optimized taking into account all the available experimental thermochemical and phase diagram information from the literature. Each liquid was described as a substitutional solution, and a Redlich-Kister formalism was used for the excess Gibbs energy.     

Thermodynamic optimisation of the Pb–Tl binary system

The phase diagram of the Pb–Tl binary system is experimentally well determined. Experimental thermodynamic values for all the phases involved are also available. For the liquid phase the temperature dependence of the enthalpy of mixing is also determined. In the present contribution, a consistent set of Gibbs energy functions of all the phases is obtained using the Redlich–Kister polynomial. The adjustable model parameters were determined by least-squares fit to the experimental data. A satisfactory agreement between experimental and calculated values is observed.     

Magnetoresistance of the La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal

The dependence of the resistance ρ of the La_0.7Ca_0.3MnO₃ single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero field ρ(T) and by the shift of the transition temperature T _C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of this single crystal is controlled by a change in the activation energy in the magnetic field.     

Chemical and phase composition of nanosized oxide and passive films on Ni-Cr alloys. II. XPS analysis of films produced by anodic passivation of alloys in 1 N H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

XPS data of thin (1 to 2 nm) oxide films formed by the anodic passivation of Ni-2 at % Cr and Ni-6 at % Cr alloys in 1 N H₂SO₄ are discussed. Thermodynamic calculations of the solid-phase chemical reaction 3NiO + 2Cr = Cr₂O₃ + 3Ni are carried out taking into account the changes in the surface energy at the alloy-oxide film interface along with the Gibbs energy change in the alloy oxidation reaction.