Thermodynamic properties of nickel-sulfur melts

A correlation is presented for the thermodynamic properties of nickel-sulfur melts with sulfur contents less than 45 atom percent in good agreement with available experimental data. The correlation is mathematically equivalent to assuming the presence of distinct chemical species in the liquid, with physical interactions between the species being described by the three-suffix Margules equations with zero ternary interactions along with the regular solution assumption. The model furnishes directly information on the saturation with solid nickel, and is apparently able to describe the properties of unstable phases over a surprisingly large range of temperature (908–1726 K). This best correlation was found with species that are present in the solid phase (Ni₃S₂,NiS), along with monoatomic nickel.     

Limitations of a regular associated solution approximation in describing the thermodynamic behaviour of complex liquid alloys

The validity of the regular associated solution (RAS) model for describing the thermodynamic properties of complex liquid alloys has been analysed by applying it to the Cu-In system. The presence of Cu₃In as the associated species in equilibrium with the free atoms in the liquid state was assumed. Liquid copper-indium alloys exhibit a very complex thermodynamic behaviour where the deviations from ideality of activities and integral enthalpy of mixing vary from positive to strongly negative and the properties are strongly temperature dependent. It is seen that a regular solution type interaction among species is insufficient to model the thermodynamic properties of liquid Cu-In alloys and the temperature dependence of interaction energies among the species has to be taken into account. A modified associated solution model incorporating volume effects and temperature dependence of interaction energies could successfully describe the thermodynamic properties of liquid Cu-In alloys.     

Cluster Monte Carlo and numerical mean field analysis for the water liquid-liquid phase transition

Using Wolff's cluster Monte Carlo simulations and numerical minimization within a mean field approach, we study the low temperature phase diagram of water, adopting a cell model that reproduces the known properties of water in its fluid phases. Both methods allow us to study the thermodynamic behavior of water at temperatures, where other numerical approaches - both Monte Carlo and molecular dynamics - are seriously hampered by the large increase of the correlation times. The cluster algorithm also allows us to emphasize that the liquid-liquid phase transition corresponds to the percolation transition of tetrahedrally ordered water molecules.     

多溴代吩噁噻热力学性质的理论计算

采用密度泛函理论方法计算了135个多溴代吩嗯噻在298.15 K和101.325 kPa时其理想气体状态的一些热力学性质的数值;研究这些性质与溴原子取代数目和位置的关系;预测多溴代吩噁噻异构体的相对稳定性.结果表明:多溴代吩嗯噻的热力学性质与溴原子取代数目和位置有良好的相关性,相关系数平方R2值接近1.000;多溴代吩噁噻异构体的相对稳定性主要由能量因素所决定且与多氯代吩嗯噻基本一致;吩噁噻的溴化作用与氯化作用,随卤原子数目的增加在热力学上难易程度的变化情况不同.     

Relationship between activity and three phase boundary in the ternary phase diagram

Theoretical formulae have been derived for determining the activity along a three-phase boundary in a three component system. The activities can be calculated from ternary phase diagrams from the partial thermodynamic properties and the use of a single integration constant. The latter is calculated from the binary phase diagrams. The formulae are rigorous and no assumption is made.     

Quantitative simultaneous fit to the liquidus surface and thermodynamic data for the GaInSb system using an associated solution model for the liquid

The liquidus surface and extensive thermodynamic properties in the Ga-In-Sb system are fit simultaneously in a quantitatively satisfactory manner. The Ga_uIn_l-uSb solid solution phase is described as quasiregular in the components GaSb and InSb. The liquid phase is assumed to consist of the species, Ga, In, Sb, GaSb, and InSb which contribute to the excess Gibbs energy of mixing by quadratic and cubic terms in the species mole fractions. The simplest version of this model that leads to an asymmetric behavior of the component chemical potentials in the Ga-Sb and In-Sb systems is identified and found to be adequate. Contrary to common usage in the literature it is not assumed a priori that the relative (to its pure liquid elements) heat capacity of CaSb(s) (or InSb(?)) is equal to that of GaSb(?) (inSb(s)). This assumption is generally incorrect for associated solution models. Moreover, the parameters of the liquid phase are constrained so that the enthalpy and entropy of mixing of GaSb(?) at the melting point of GaSb(s) are properly related to the enthalpy and entropy of formation of GaSb(s). Two similar constraints are used for InSb(l).     

Equilibrium between MB2 (M=Ti,Zr,Hf) UHTC and Ni: A thermodynamic database for the B-Hf-Ni-Ti-Zr system

MB₂ (M=Ti,Zr,Hf) Ultra High Temperature Ceramics (UHTCs) are characterised by melting temperatures in excess of 3000 °C and have structural, physical, transport, and thermodynamic properties suitable for use as thermal barriers in extreme environments. It is then necessary to investigate interactions of the diborides with the materials they are supposed to protect. To this end it has been developed a CALPHAD thermodynamic database for the calculation of phase equilibria and thermodynamic properties in the quinary system B-Ni-Ti-Zr-Hf. The database contains thermodynamic parameters for all the phases included in the 10 binary and 10 ternary sub-systems of B-Ni-Ti-Zr-Hf. A few binary systems (B-Hf, B-Ti, B-Zr, Hf-Ni, Ni-Zr) have been slightly modified with respect to the previous assessments and several ternary systems (B-Hf-Ni, B-Ni-Ti, B-Ni-Zr, B-Hf-Zr, B-Ti-Zr, Hf-Ni-Ti, Hf-Ni-Zr, Hf-Ti-Zr, Ni-Ti-Zr) have been completely assessed or re-assessed in this work with particular attention to the self-consistency of the models adopted.     

A thermodynamic analysis of the bi-s system by an associated solution model

The available phase equilibria and thermodynamic data have been used to thermodynamically analyse the Bi-S system. An associated solution model is used to describe the thermodynamic properties of the liquid phase by assuming the presence of ‘BiS’ species in the liquid in addition to ‘Bi’ and ‘S’ species. The phase diagram and the thermodynamic properties, calculated from the optimized parameters, agree very well with the experimental data.     

A thermodynamic assessment of the Cr–Mo system using CE-CVM

A thermodynamic assessment of the condensed phase region of the Cr–Mo system has been carried out on the basis of available experimental thermodynamic and phase equilibria data. The Gibbs energy of the BCC_A2 solid phase was described by using octahedron–rhombohedron–cube (ORC) approximation of the Cluster Expansion and Cluster Variation Methods (CE-CVM), while a sub-regular solution model was used for describing Gibbs energy of the liquid phase. An optimal set of parameters has been obtained for describing the Gibbs energies of the liquid and solid phases in the Cr–Mo binary system by simultaneous optimization of all experimental data. The calculated phase diagram and thermodynamic properties are in good agreement with experimental data. The relevance of CE-CVM has been demonstrated in the present case by computing first to fifth neighbor short range order (sro) parameters of the solid phase as a function of composition at various temperatures.     

多溴二苯并噻吩系列化合物的热力学性质及稳定性的密度泛函理论

本文在298.15 K和1.013×10~5Pa时,根据密度泛函理论(DFT),使用Gaussian 03程序,在B3LYP/6-31G(d)水平上计算117个多溴二苯噻吩系列化合物(PBDTs),得各分子的热力学性质。设计等键反应,计算PBDTs系列化合物的标准生成热Δ_fH~(?)和标准生成自由能Δ_fG~(?)。同时用程序Origin7.5将这些热力学参数与溴原子的取代位置及取代数目线性回归,求出相关方程,研究表明:热力学参数、标准生成热、标准生成自由能与溴原子的取代位置及取代数目之间关系极密切。根据标准生成自由能的相对大小,本文从理论上求得该化合物异构体的相对稳定性顺序。本文研究该化合物热力学性质及其稳定性,对于研究其生成、降解以及对环境的潜在威胁具有重要意义。     

An application of satellite-derived sea surface temperature data to the Australian fishing industry in near real-time

Abstract

A four-year project conducted from 1981 to 1985 examined the application of satellite-derived near real-time sea surface temperature data in assisting the Tuna fishing industry located along the southwestern coast of Australia. The satellite imagery employed was obtained from the NOAA series of polar orbiting satellites. Since the southern bluefin tuna is a pelagic species, it had been anticipated that a good correlation would be found between sea surface temperatures and catches. Early experimental results tended to confirm that view, but a number of anomalies existed in those results. It is now suggested that a weak correlation exists between temperature and catches, but this is due to localized factors. A theory justifying this assumption is given.     

Activities and ternary phase diagrams

A set of theoretical formulae for calculating activities along the liquid surface in ternary phase diagrams has been presented. These formulae are rigorous since no assumption is made in the derivation. The expressions are generalized and can be simplified to the forms presented by Pelton, Chou, Elliott and Gokcen under certain conditions. In practice, the activity of the components are desired at a fixed temperature instead of a variable temperature like that along a liquid surface. Under this situation, with reasonable assumptions the equations can be further simplified such that they do not contain any partial thermodynamic properties. Activities can then be readily calculated from phase diagrams. The method presented in this paper is for a ternary system and can be extended to multicomponent systems.     

Critical assessment of thermodynamic properties of important polycyclic aromatic hydrocarbon compounds (PAHs) in coal tar pitch at typical temperature ranges of the carbonization process

Because of the importance of thermodynamic behavior of Polycyclic Aromatic Hydrocarbon (PAH) compounds in coal tar pitch carbonization process, a thermodynamic model for the prediction of thermodynamic properties of PAH compounds is developed. Heat capacity functions as well as standard thermodynamic properties of PAHs in solid, liquid, and gas states are estimated using modified group additivity algorithms first proposed by Richard and Helgeson and thermal physical data of those PAHs for which enough experimental data exists in the literature. For the first time, initial calculated thermodynamic properties of PAHs are optimized by applying the CALPHAD (CaLculation of PHAse Diagrams) approach where all thermodynamic data are rendered consistent with phase transitions and vapor pressure data. The heat capacity function of PAHs exhibiting thermal anomaly behavior is modeled as a specific case. This modeling is performed using an order-disorder approach with the Compound Energy Formalism (CEF). Good agreement has been obtained between the predicted thermodynamic properties of PAHs and available experimental data. The proposed model has improved the predictive capacity compared to that of the previous models predicting thermodynamic properties of PAHs at typical temperature ranges of the carbonization process. The application of the model to predict the thermodynamic properties of major and high molecular weight PAHs available in coal tar pitch has been discussed.     

Refinement of the thermodynamic modeling of the Nb–Ni system

The Nb–Ni system is reassessed on the basis of a critical literature review involving recent experimental data. These newly published experimental data include the phase relation associated with the NbNi₈ phase, phase transition temperatures resulting from selected alloys, all invariant reaction temperatures, and enthalpies of mixing of liquid, as well as the crystallographic data on the μ$\mu$ (Nb₇Ni₆) phase. A consistent thermodynamic data set for the Nb–Ni system is obtained by optimization of the selected experimental values. The calculated phase diagram, crystallographic properties and thermodynamic properties agree reasonably with the experimental data. Noticeable improvements have been made, compared with the previous thermodynamic optimizations.     

Phase equilibria and microstructure development in Mg-rich Mg-Gd-Sr alloys: Experiments and CALPHAD assessment

Mg-Sr alloys are promising to fabricate orthopedic implants. The alloying of rare earth elements such as Gd may improve the comprehensive mechanical properties of Mg-Sr alloys. The information on the phase diagram and the microstructure development are required to design chemical composition and microstructure of Gd alloyed Mg-Sr alloys. The phase equilibria and the microstructure development in Mg-rich Mg-Gd-Sr alloys (Gd, Sr < 30 at. %) are experimentally investigated via phase identification, chemical analysis, and microstructure observation with respect to the annealed ternary alloys. The onset temperatures of liquid formation are measured by differential scanning calorimetry. A thermodynamic database of the Mg-rich Mg–Gd–Sr ternary system is developed for the first time via CALPHAD (CALculation of PHAse Diagram) approach assisted by First-Principles calculations. The thermodynamic calculations with the developed database enable a well reproduction of the experimental findings and the physical-metallurgical understanding of the microstructure formation in solidification and annealing.     

解析式状态方程计算含临界点方阱流体的性质

含临界区流体的物性计算一直是热力学领域的难点。一般认为，解析式状态方程不可能同时很好地计算远离临界点和靠近临界点流体的热力学性质。该文目的就是验证解析式方程在计算热力学性质特别是接近临界点附近的热力学性质适用性。通过计算机分子模拟数据，研究了各种解析式状态方程计算接近临界区的方阱流体的物性的可能性，结果表明，经过参数重新拟合新的解析式方程，可以很好地计算方阱流体的相平衡、密度等性质，直到对比温度接近临界点0．05处。临界点温度、压力和密度的计算值和分子模拟值也基本符合。该文结果可以为解析式方程计算范围的扩大提供依据，从而试图解析式在工程方面有更加广泛的应用。     

Exploring the protein folding free energy landscape: coupling replica exchange method with P3ME/RESPA algorithm

A highly parallel replica exchange method (REM) that couples with a newly developed molecular dynamics algorithm particle-particle particle-mesh Ewald (P3ME)/RESPA has been proposed for efficient sampling of protein folding free energy landscape. The algorithm is then applied to two separate protein systems, beta-hairpin and a designed protein Trp-cage. The all-atom OPLSAA force field with an explicit solvent model is used for both protein folding simulations. Up to 64 replicas of solvated protein systems are simulated in parallel over a wide range of temperatures. The combined trajectories in temperature and configurational space allow a replica to overcome free energy barriers present at low temperatures. These large scale simulations reveal detailed results on folding mechanisms, intermediate state structures, thermodynamic properties and the temperature dependences for both protein systems.     

Modified general solution model for interstitial solid solution

By introducing two sublattices to the general solution model, a modified model for studying the thermodynamic properties of interstitial solid solutions in multicomponent steels is suggested. The excess Gibbs free energy of mixing in Fe-Σi-C steel can be calculated from the modified model with the thermodynamic parameters of ternary Fe-i-C and binary i-j systems that are easily obtained. As an example, Ae₃ temperatures for pro-eutectoid ferrite formation in nine steels have been calculated from the modified general solution model and compared with that from the two-sublattice model using the interactions among multicomponents or not and that from ThermoCalc software. The relative standard deviation and root-mean-square error between the experimental Ae₃ temperatures and the values calculated from the modified model are 0.57% and 7.2K, respectively. It can be concluded that the modified general solution model for interstitial solid solutions is acceptable.