Showing papers in "Calphad-computer Coupling of Phase Diagrams and Thermochemistry in 1999"

IVTANTHERMO for Windows — database on thermodynamic properties and related software

Abstract: A new version of the software package IVTANTHERMO for Windows intended for thermodynamic modelling of complex chemically reacting systems is described. The package includes an extensive database on thermodynamic properties of individual substances, programs for the database handling and a program, which allows the calculation of equilibrium composition and thermodynamic properties of the system to be examined. The software is intended for scientists, chemical engineers and students.

Thermodynamic modelling of the system titanium-oxygen☆

Abstract: The complete titanium-oxygen system from metallic titanium to gaseous oxygen including Magneli phases was critically assessed between 298 K and liquidus temperatures and at a pressure of 1 bar. All available experimental T-x phase diagram and thermodynamic data — all in all about 600 data points — were applied to model the Gibbs energies of totally eighteen phases. Of these, twelve were treated as line compounds. Gibbs energies as a function of temperature and composition using sublattice models were optimized for five condensed mixture phases. The ideal approach was accepted for the gas phase. The calculations were carried out using ChemSage.

Thermodynamic assessment of the Pu-U, Pu-Zr, and Pu-U-Zr systems

Abstract: Based on thermodynamic and phase diagram data, the Gibbs energies of mixing of the solution phases in the Pu-U and Pu-Zr systems were calculated using an optimization procedure. The use of thermodynamic data in the optimization made it possible to accurately calculate thermodynamic properties as well as the phase diagrams, which were in good agreement with the respective experimental values. The Pu-U-Zr ternary isotherms were calculated by using the optimized parameters of the three binary subsystems. The results agreed reasonably well with the experimental ones.

Thermodynamic evaluation of the Germanium — Tellurium system

Abstract: In order to optimize the binary Ge-Te system available experimental data were critically compiled from the literature. The cubic high-temperature β-phase and the rhomboedric room-temperature α-phase were described by a two-sublattice model with one kind of defect (vacancies on germanium sites). The room-temperature orthorhombic γ-phase was treated as a stoichiometric compound, as there is a lack of information about its solubility. The liquid phase was modelled by the the associate model with one kind of associate, namely ‘GeTe’. A set of thermodynamic parameters was obtained and the calculated phase diagram is presented.

Thermodynamic reassessment of Fe-Cr-Ni system with emphasis on the iron-rich corner

Abstract: Thermodynamic reoptimization has been made for the Fe-Cr-Ni system with emphasis on the iron-rich corner of the system. New ternary substitutional-solution interaction parameters were optimized for the liquid, fcc and bcc phases and a new Gibbs energy expression was suggested for one hypothetical component of the sigma phase. The rest of the data concerning the binary subsystems and the sigma phase were taken from earlier assessed Fe-Cr-Ni descriptions. The calculated results were validated with numerous experiments of phase equilibria, solute partition and component activity. The results were also compared with those of two earlier Fe-Cr-Ni assessments showing improved or equal agreement with most experiments. Only for the liquidus temperatures at high chromium and nickel contents (above 30wt%) is the agreement worse than in the earlier assessments.

Modeling the charge compensation effect in silica-rich Na2O-K2O-Al2O3-SiO2 melts

Abstract: At high SiO2 contents, a model of Na2O-K2O-Al2O3-SiO2 melts must take into account the “charge compensation effect” whereby the replacement of a tetravalent Si4+ by a trivalent Al3+ in the silicate network is facilitated by the formation of (NaAl)4+ or (KAl)4+ issociates. This effect has been taken into account in the quasichemical model by treating the (NaAl)4+ and (KAl)4+ associates as separate species in the melt, which is then formally treated as consisting of the components NaO 1 2 , KO 1 2 , AlO 3 2 , SiO2, (NaAl)O2 and (KAl)O2. Optimizations of the Na2O-Al2O3-SiO2, K2O-Al2O3-SiO2 and NaAlSiO4-KAlSiO4-SiO2 systems at high SiO2 contents are reported.

Thermodynamic assessment of the Co-Ta system

Abstract: The phase equilibria and thermodynamic properties of the binary Co-Ta system were analyzed and a complete thermodynamic description of the binary system was obtained with the CALPHAD technique using a computerized optimization procedure. The thermodynamic descriptions of pure Co and Ta elements were taken from the SGTE database. Based on the experimental data, six binary intermetallic compounds were considered. They are three Laves phases, μ phase, θ phase and Co 7 Ta 2 phase. The last two compounds are treated as stoichiometric compounds. Good agreement was obtained between calculated results and experimental data in the binary system.

The thermodynamic database MALT

Abstract: The objectives of the development of the thermodynamic database MALT are described together with its main characteristic features. The database, which contains about 5000 species, also composes software for calculation of chemical equilibria and construction of generalized chemical potential diagrams. Discussion is made on the quality of the thermodynamic data to be used in the advanced software for calculating complex chemical equilibria in multicomponent systems and the importance of the chemical potential diagrams for checking the interconsistency of data in a visual manner is stressed.

Application of thermodynamic modeling to slag-metal equilibria in steelmaking☆

Abstract: The knowledge of the non-metallic phases in equilibrium with liquid steel is very important to the design and control of the results of steelmaking operations, in particular deoxidation, desulfurization and inclusion shape control. Thus, through the control of steel and slag composition it is possible, for instance, to tailor non-metallic inclusions to achieve maximum deformability, to avoid nozzle clogging in continuous casting and to optimize the use of deoxidants. However, the solution of this type of problems requires adequate thermodynamic models and corresponding databases both for the metal phase and for the slag. Close interaction with the steelmaking shop makes it possible a) to evaluate the calculation needs for solving these problems, b) apply the selected models and databases to these questions and c) have a feedback with respect to how adequate the solution is to the actual problem. In this work the current models used for these applications are briefly reviewed, their limitations highlighted and the results of their applications both to laboratory and to plant data are presented and compared.

Thermodynamic description of the system Ti-Cr-C

Abstract: A thermodynamic description of the Ti-Cr-C ternary system is obtained based on a critical evaluation and limited experimental verification of the literature data reported on the ternary system and its binary subsystems. Using a minimum of only 3 adjustable parameters these calculations allow us to reproduce the experimentally determined solidification sequence, the invariant reaction temperatures, and the compositions of the participating liquid phase. The only exception is the reaction temperature for the ternary eutectic L ↔ TiC + Cr 7 C 3 + Cr 3 C 2 . This discrepany seems to be connected with the difficulty to calculate the binary eutectic L ↔ Cr 7 C 3 + Cr 3 C 2 indicating that the simple model used for the description of the liquid phase should be replaced by a more complex model to obtain a better fit for this reaction temperature.

Thermodynamic assessment of the CaOB2O3 system

Abstract: The CaO-B 2 O 3 pseudo-binary system has been assessed thermodynamically. A two-sublattice ionic solution model, (Ca +2 )p(O −2 ,BO 3 −3 ,B 4 O 7 2,B 3 O 4.5 ) Q was adopted to describe the liquid phase. All the solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the experimental data on both phase diagram and thermodynamic properties was obtained by using the CALPHAD technique. A comparison between the calculated results and experimental data as well as a previous assessment is presented.

The phase relations in the FeO-MgO-Al2O3-SiO2 system: assessment of thermodynamic properties and phase equilibria at pressures up to 30 GPa

Abstract: Thermodynamic parameters for minerals in the FeO-MgO-Al 2 O 3 -SiO 2 (FMAS) system have been assessed from phase equilibria at pressures up to 30 GPa. All solid solution phases except orthopyroxene have been described by the sublattice model. Calculated phase diagrams of end member systems, exchange reactions in the FMAS system, phase equilibria for fixed compositions at pressures up to 30 GPa are in a reasonable agreement with the experimental data. The most critical data in the MgO-Al 2 O 3 -SiO 2 (MAS) system were compositions of garnet in equilibrium with Mg-rich ilmenite at 1273 K. To reproduce the experimentally observed Fe-Mg partition between perovskite and magnesiowustite, it is necessary to take into account the presence of Fe 3+ ions in perovskite. The phase diagram of the FMAS system for pyrolite composition has been calculated in the temperature range of 1500 to 2400 K at pressures between 12 to 32 GPa.

Thermodynamic description of solution phases of systems Fe-Cr-Si and Fe-Ni-Si with low silicon contents and with application to stainless steels

Abstract: A thermodynamic optimization has been made for the solution phases of the ternary systems Fe-Cr-Si and Fe-Ni-Si in the iron-rich corner. Ternary substitutional-solution interaction parameters were optimized for the liquid, fcc and bcc phases, and the lower-order data were taken from the earlier assessed sub-systems. The calculated results were validated with experiments of phase equilibria and component activities in liquid. The new data were then added to the existing database of multicomponent steels and calculations were carried out for certain silicon containing stainless steels. As a result, clearly improved agreement was obtained between calculations and experiments concerning the liquidus temperatures and the solid/liquid partitioning of silicon in these steels.

Predicting of the thermodynamic properties for the ternary system Ga-Sb-Bi

Abstract: R-function method for predicting the ternary thermodynamic properties from its binary ones was applied to the ternary system Pb−Bi−Mg. Activities, activity coefficients, partial and integral molar quantities for Pb, Bi and Mg for the quasibinary sections Pb-X (X=B, C, D, E, F) in the investigated ternary system Pb−Bi−Mg calculated by means ofR-function method are given in this paper. Also, it was determined that results obtained byR-function method reach a good agreement with the experimental results obtained by Oelsen calorimetry.

Experimental study of thermal expansion and phase transformations in iron-rich Fe-Al alloys☆

Abstract: A series of Fe-Al alloys with various contents of aluminium (from 1 to 10 weight percent) was investigated by X-ray diffraction. The unit cell parameters and molar volumes of these alloys were measured at ambient conditions. The thermal expansions of two alloys (with 5 and 10 weight % Al) were obtained in the temperature range of 293–1370 K. The specimen was heated by passing an electrical current through the sample. The sample consists of a carbon strip as a heater and a Fe-Al alloy powder pressed onto its surface. A Pt-13% Rh thermocouple was used for temperature determination. In order to prevent oxidation of the specimen, the experiments were carried out in an argon-hydrogen flow. The spectra were analyzed and unit cell parameters at different temperatures were calculated using the General Structural Analysis System (GSAS) program. The phase transformation from bcc to fcc structure in the Fe-5%Al alloy was observed at temperatures between 1203(5) and 1238(5) K; the Fe-10%Al alloy transformed to a structure with a primitive cubic lattice at temperatures above 1300 K.

Thermodynamic evaluation of the system silicon — Tellurium

Abstract: Thermochemical and phase diagram data taken from literature have been critically evaluated with respect to consistency in order to provide the Gibbs energies of liquid and solid phases. The liquid phase was described with the use of the associated solution model, while low and high temperature modifications of Si2Te3 are given as stoichiometric. Phase diagram and thermodynamic functions calculated from the set of optimized parametric descriptions of the Gibbs energies are presented.

Thermodynamic description of Cr-P AND Fe-Cr-P systems at low phosphorus contents

Abstract: Thermodynamic optimization of systems Cr-P and Fe-Cr-P has been made by using classical thermodynamic models for describing the properties of the individual phases of the systems. The thermodynamic parameters of sub-systems Fe-Cr and Fe-P for Fe-Cr-P were taken from earlier assessments and the parameters of systems Cr-P and Fe-Cr-P were optimized by using recently measured activity and Gibbs energy data, and experimental phase equilibrium data. The present descriptions are valid at phosphorus contents up to X p =0.25 (≈16.6 wt%P).

Some problems arising from two sublattice modelling of ordered phases

Abstract: Although two (or effectively two) sublattice modelling of ordered phases has been the norm in carrying out phase diagram assessments, it is argued that this kind of modelling should, in general, be discouraged for these phases. Two-sublattice modelling gives a Gibbs energy minimum (with reference states at the same temperature and with the same parent structure as the ordered phase) for every ordered phase, irrespective of its composition. In doing so, it fails to take into account that at most ordered phase compositions there are only kinks and not minima in the Gibbs energy-composition curve with respect to these reference states. Kinks can be obtained if the ordered phases are modelled with more than two sublattices. Because of the incorrect shape of the Gibbs energy-composition curve when two-sublattice modelling is used, there is an excessive but unnecessary demand on the sublattice L parameter terms in the excess Gibbs energy for the fitting of experimental results. This often leads to unreliable extrapolations of the Gibbs energy-composition curves.

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

Abstract: 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.

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

Abstract: 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.