Nacl—Bacl2—Srcl2三元熔盐相图的计算

本文运用作者提出的从三个对应的二元系的热力学性质预示三元溶液的热力学性质的新对称几何模型,推导得到三元溶液中三个组元的偏摩尔热力学性质的数学表达式。进而将这一结果应用于NaCl-BaCl_2-SrCl_2三元熔盐相图的计算中,得到此三元系的液相析出面及若干等温截面。计算所得结果与实测结果偏差小于5℃,说明此模型在一些熔盐体系中有较好的适用性。     

CALCULATION OF NaCl-BaCl_2-SrCl_2 PHASE DIAGRAM

The mathematical formulas are given for calculating the partial molar thermodynamic proper-ties in a ternary system from its three corresponding binary systems based on the new ternarysymmetric model presented by the authors in the foregoing paper.Applying this model toNaCl-BaCl_2-SrCl_2 system,the phase diagram of which as well as some isothermal sectionshave been calculated.The devations of temperature between the calculated and experimen-tal diagrams are less than five degrees.     

Ba-eu (barium-europium)

Several thermodynamic models for calculating binary phase diagrams published in the literature have been reevaluated. Problems in some of these models are already evident in the models themselves and may also be seen in the resulting calculated phase diagrams. When a calculation is attempted, thermodynamic models with quite different formulations may result in very similar proposed phase diagrams. In such cases, if experimental data of a binary phase diagram can be represented reasonably well by several different thermodynamic models, a simpler model often provides the clearest insight into the basic properties of the system. If a calculated phase diagram results in unusual phase relationships, the adopted thermodynamic model may be inappropriate or may involve unrealistic parameters. If the thermodynamic model is clearly unrealistic and yet the calculated phase diagram appears to be normal, errors in calculation or in interpretation may be suspect. Various examples of unlikely combinations of thermodynamic models and phase diagrams are discussed.     

Reevaluation of thermodynamic models for phase diagram evaluation

Several thermodynamic models for calculating binary phase diagrams published in the literature have been reevaluated. Problems in some of these models are already evident in the models themselves and may also be seen in the resulting calculated phase diagrams. When a calculation is attempted, thermodynamic models with quite different formulations may result in very similar proposed phase diagrams. In such cases, if experimental data of a binary phase diagram can be represented reasonably well by several different thermodynamic models, a simpler model often provides the clearest insight into the basic properties of the system. If a calculated phase diagram results in unusual phase relationships, the adopted thermodynamic model may be inappropriate or may involve unrealistic parameters. If the thermodynamic model is clearly unrealistic and yet the calculated phase diagram appears to be normal, errors in calculation or in interpretation may be suspect. Various examples of unlikely combinations of thermodynamic models and phase diagrams are discussed.     

Calculations of phase diagrams in associated solution model

The development of an ideal associated solution model concerned with complexes of various compositions, sizes, and shapes is described. Such models were used earlier to calculate thermodynamic characteristics and the position of the liquidus line for binary eutectic systems as well as those having a stable compound in the solid phase. In all the cases, the model parameters were not adjusted but were estimated from melting temperatures of the components. The latest studies deal with the influence of arbitrary stoichiometry associates on the equilibrium thermodynamic properties of liquid alloys. The application of the model to eutectic systems and systems having an unlimited miscibility in solid and liquid states close to the liquidus has been considered. It was shown that if the difference in melting temperatures of the components was small, different types of fusibility diagrams were possible: eutectic diagrams, cigar-shaped diagrams, or diagrams with upper or lower azeotropic points. Peritectic transformations could take place if the difference in melting temperatures of the components were large.     

THERMODYNAMIC CALCULATION MODELS FOR TiO_2-BASED SLAG MELTS

1.IntroductionTheincreasingdemandsf0rlownitrogensteelproductsgiveriset0greatenthusiaJsmtouseTiO2-basedfluxfordenitrogeniZationofsteel[1-3].ManyexperimentscondrmedthatTi0z-basedslagshavehighernitridecaPacitiesandaPpeartobeonekind0fthemosteffectivefiuxesf0rdeIiltrogenization.Butasfarastherm0dynamicstudiesareconcerned,littleworkhasbeenreported0nthethermodynamiccalculationm0delsforTiO2-base'slags[4],especiallyf0rmulticomponentslagswithtitania-Inadditi0n,aJsaresultofusingvanadium-bearingtitani…     

The influence of solution-model complexity on phase diagram prediction

In the derivation of phase diagrams using solid- and liquid-solution thermodynamic equilibria, thermodynamic models are used to extrapolate experimental data to a broader range of compositions and temperatures. Such models have historically increased in complexity from the regular-solution formalism, with regard to both temperature and composition dependence of parameters. The regular, quasi-regular, subsubregular, and quasi-subsubregular models have been applied to existing thermodynamic data for four“simple” metallic systems of differing types (Cu-Ni, Pb-Ag, Sn-Zn, and Ge-Mg) to illustrate the effect of more accurate thermodynamic modeling on the resulting predicted phase diagrams. Comparison with the actual phase diagrams demonstrates the relative importance of“nonregularity” in the solution with regard to both composition and temperature in the accuracy of phase diagram prediction. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October 21-23,1991, in Cincinnati, OH. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.     

由三元相图计算活度

采用熔化自由能法、标准生成自由能法和化学平衡法推导出利用8种类型的三元相图计算活度的公式,覆盖了三元相图的点、线、面全部范围。公式本身没有引进假设和近似。这8种类型的三元相图涵盖了有液相面各种类型的三元相图。本研究的计算方法和计算公式可以应用于各种复杂的三元相图,该方法也可以推广到三元等温截面相图和三元以上的多元相图。     

Phase diagrams and thermodynamic properties of rare earth-bismuth systems

A survey is given of rare earth-bismuth phase diagrams and of crystallographic and thermodynamic properties of the intermetallic compounds occuring in the various rare earth-bismuth systems. Observed trends and regularities are briefly discussed. A more detailed investigation is presented for the Tm---Bi phase diagram.     

Melting points of the metallic elements having the face-centered cubic,body-centered cubic,and close-packed hexagonal structures

The melting points of the fcc, bcc and cph structures of a majority of the metallic elements have been calculated from the thermodynamic data in the literature. This information is useful in estimating phase diagrams that represent metastable structures. An example is the extension of the liquid-fcc solid solution two-phase field to pure Cr for the Ni-Cr system. There are often marked differences in melting points between the different structures for a given metal.     

Thermodynamic analysis of alloys Ti–Al, Ti–V, Al–V and Ti–Al–V

Thermodynamic analysis of three binary Ti-based alloys: Ti–Al, Ti–V, and Al–V, as well as ternary alloy Ti–Al–V, is shown in this paper. Thermodynamic analysis involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2000, 2073, 2200 and 2273 K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.     

Topology of potential phase diagrams composed of three chemical elements

A detailed analysis of the topology of two-dimensional isothermal potential phase diagrams for systems composed of three chemical elements is presented. Chemical potentials (or derived properties as activities or partial pressures) of two independent components or their combinations are used as coordinates of such diagrams. The chemical potentials of other species are constant at the given temperature (i.e., stoichiometric, single-species condensed phases, or components of a multicomponent phase of fixed composition). It was shown that only invariant point can change the topology of the diagram. A method for the determination of invariant points is proposed. The set of invariant points is divided into four classes, and each class is demonstrated by a practical example.     

Thermodynamic Optimization and Calculation of the HoCl3-MCl (M = Na, K, Rb, Cs) Systems

According to measured experimental phase diagram data and thermodynamic data, the HoCl₃-MCl (M = Na, K, Rb, Cs) phase diagrams were determined by the CALPHAD technique. The Gibbs energies of liquid phases in these systems have been optimized and calculated by the modified quasi-chemical model in the pair-approximation for short-range ordering. A series of thermodynamic functions have been optimized and calculated on the basis of an interactive computer-assisted analysis. The results show that the thermodynamic properties and phase diagrams are self-consistent. The optimized results for the systems are discussed.     

Coherent phase diagrams

Phase equilibria in coherent solids differ significantly from equilibria in fluids or incoherent solids. Gibbs' phase rule usually does not apply, the field lines on a phase diagram do not coincide with the equilibrium phase compositions, phase compositions in a two-phase field depend on the bulk alloy composition and, for a given set of imposed thermodynamic variables, several equilibrium states may exist. These conditions place significant constraints on the use of coherent phase diagrams. This paper discusses some aspects of phase equilibria that are unique to coherent systems and how phase information may be conveyed when phase stability diagrams are used in lieu of coherent phase diagrams. The utility of phase stability diagrams lies in their ability to display graphically the equilibrium states of a two-phase coherent system as a function of alloy composition (in much the same way that Gibbs energy vs composition curves show equilibrium states for a fluid system).     

熔盐腐蚀电化学

本文从热力学和动力学这两方面阐述了熔盐腐蚀的电化学研究方法。总结了金属在熔融氯化物、硫酸盐、碳酸盐、硝酸盐中的E-pO_2-图,Na-M-S-O 相图和金属氧化物在熔融硫酸盐中的溶解度。讨论了弱极化曲线拟合方程和腐蚀电流密度与微分极化电阻之间的关系。电化学技术是评价合金耐蚀性能,监控熔盐腐蚀速度的有效工具。     

Critical Systematic Evaluation and Thermodynamic Optimization of the Mn-RE System (RE = Tb,Dy, Ho,Er, Tm and Lu) with Key Experiments for the Mn-Dy System

Critical evaluation and optimization of all available phase diagrams and thermodynamic data for the Mn-RE (RE = Tb, Dy, Ho, Er, Tm, and Lu) systems has been conducted to obtain reliable thermodynamic functions of all the phases in the systems. Key experiments for the Mn-Dy system were performed using DSC and solution calorimeter. In the thermodynamic modeling, it is found that the Mn-RE systems show systematic changes in the phase diagrams and thermodynamic properties such as enthalpy of mixing in liquid state in the order of periodic number in the lanthanide series. The systematic thermodynamic modeling approach for RE elements allow to resolve inconsistencies in the experimental data and estimate unknown thermodynamic properties and phase equilibria of Mn-RE system.     

Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System

A thermodynamic computer dataset for the Y-Si-C-O system was used for calculations of multicomponent, multiphase reactions. The phase reactions of yttrium silicate coatings for the oxidation protection of C/SiC-based composites were analyzed. They were simulated as a function of the temperature and other environmental conditions. To illustrate the high temperature behavior of the coatings, isothermal sections, isopleths, pseudo-binary and -ternary diagrams, phase fraction diagrams, volatility diagrams and potential phase diagrams are presented. Additionally to the thermodynamic aspects, mass balance criteria were taken into account for the analysis of the active/passive oxidation in the coating system. This article was presented at the MultiComponent Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12–16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.     

Effect of Intercritical Annealing Temperature on Phase Transformations in Medium Carbon Dual Phase Steels

This paper presents a study concerning phase transformations during quenching of a medium carbon dual phase steel using thermodynamic equilibrium calculations and dilatometry. Medium carbon steel was subjected to the intermediate quenching to produce a fine grained ferrite/martensite dual phase steel. 4 samples quenched after intercritical annealing at 725, 730, 740, and 750 °C. Martensite-start and bainite-start temperatures were calculated from dilatometric curves using plastodilotemeter. Experimental findings are supported by calculated phase diagrams and equilibrium phase compositions using ThermoCalc^® and calculations from different empirical formulas. It is concluded that martensite-start temperature depend on chemical composition and grain size of austenite.