Patrice Chartrand

FactSage Thermochemical Software and Databases

Abstract This paper presents a summary of the FactSage thermochemical software and databases. FactSage was introduced in 2001 and is the fusion of the FACT-Win/F∗A∗C∗T and ChemSage/SOLGASMIX thermochemical packages that were founded over 25 years ago. The FactSage package runs on a PC operating under Microsoft Windows® and consists of a series of information, database, calculation and manipulation modules that enable one to access and manipulate pure substances and solution databases. With the various modules one can perform a wide variety of thermochemical calculations and generate tables, graphs and figures of interest to chemical and physical metallurgists, chemical engineers, corrosion engineers, inorganic chemists, geochemists, ceramists, electrochemists, environmentalists, etc. In this article emphasis is placed on the calculation and manipulation of phase diagrams. However the reputation of FactSage has been established mainly in the field of complex chemical equilibria and process simulation where the software has unique capabilities. Some of these capabilities are also shown in this paper.

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the Al-Mg, Al-Sr, Mg-Sr, and Al-Mg-Sr systems

All available thermodynamic and phase diagram data were critically assessed for all phases in the Al-Mg, Al-Sr, and Mg-Sr systems at 1 bar pressure from room temperature to above the liquidus temperatures. For these systems, all reliable data were simultaneously optimized to obtain a set of model equations for the Gibbs energy of the liquid alloy and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the liquid. The Al-Mg-Sr ternary phase diagram was calculated from the optimized thermodynamic properties of the binary systems. Since no reliable ternary data were available, three assumptions were made: no ternary terms were added to the model parameters for the thermodynamic properties of the liquid, no ternary solid solutions are present in the system, and no ternary compound is present in the system. The calculated ternary phase diagram is thus a first approximation, which can be improved by the addition of new experimental data and can be used as a base for the calculation of phase diagrams of multicomponent systems.

On the choice of geometric thermodynamic models

A number of “geometric” models have been proposed for estimating the thermodynamic properties of a ternary solution from optimized data for its binary subsystems. Among the most common of these are the Kohler, Muggianu, Kohler/Toop, and Muggianu/Toop models. The latter two are “asymmetric” models in that one component is singled out and treated differently, whereas the first two models are “symmetric.” It is shown that the use of a symmetric model when an asymmetric model is more appropriate can often give rise to large errors. Equations are proposed for extending the symmetric/asymmetric dichotomy into N-component systems (N=3), while still permitting the flexibility to choose either a symmetric or an asymmetric model for any ternary subsystem. An improved general functional form for “ternary terms” in the excess Gibbs energy expression is also proposed. These terms are related to the effect of a third component upon the binary pair interaction energies. All the above considerations also apply when short-range ordering is taken into account by using the modified quasichemical model. Finally, some arguments in favor of the Kohler model over the Muggianu model are presented.

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.

Prediction of the thermophysical properties of molten salt fast reactor fuel from first-principles

Molten fluorides are known to show favourable thermophysical properties which make them good candidate coolants for nuclear fission reactors. Here we investigate the special case of mixtures of lithium fluoride and thorium fluoride, which act both as coolant and as fuel in the molten salt fast reactor concept. By using ab initio parameterised polarisable force fields, we show that it is possible to calculate the whole set of properties (density, thermal expansion, heat capacity, viscosity and thermal conductivity) which are necessary for assessing the heat transfer performance of the melt over the whole range of compositions and temperatures. We then deduce from our calculations several figures of merit which are important in helping the optimisation of the design of molten salt fast reactors.

Thermodynamic evaluation and optimization of the Ca-Si system

All available phase equilibria and thermodynamic data for the Ca−Si system were collected and critically evaluated. In a first step, the thermodynamic properties of Ca(g) were obtained from experimental vapor pressure data over pure Ca. The new vapor pressure of calcium over pure solid and liquid was used as a new reference to model the thermodynamic properties of the intermediate stoichiometric Ca−Si compounds together with other thermodynamic and phase diagram data found in the literature (liquidus temperatures, heat capacities, pressures of Ca, and heats of reaction). Optimization was performed to obtain the parameters of one set of model equations for the different solid and liquid phases to best reproduce all the experimental data simultaneously. In this way, the data are rendered self-consistent, discrepancies among the data are identified, and extrapolations and interpolations can be performed. For the liquid phase, the Modified Quasichemical Model in the Pair Approximation for short-range ordering was used.

Evidence of second order transition induced by the porosity in the thermal conductivity of sintered metals

In this paper, using both experimental data and theoretical modelling, we investigate the degradation of the thermal conductivity of sintered metals due simultaneously to the grain boundary thermal resistance and the porosity. We show that the porosity dependence of the thermal conductivity of sintered material from spherical particle powder, exhibits a critical behaviour associated with a second order phase transition. An analytical model with a single parameter is proposed to describe the critical behaviour of the thermal conductivity of sintered metals versus porosity.

Experimental study of the thermal conductivity of sintered tungsten: Evidence of a critical behaviour with porosity

Rear face flash experiments were performed in order to determine the thermal conductivity of sintered tungsten at room temperature. Ten different samples were synthesized with the spark plasma sintering technique. The microstructure obtained from the sintering is porous and consists of angular grains with medium sphericity. The average grain size (d) and the porosity (P) of the samples lie within the ranges of 2 mu m <= d <= 7 mu m and 0 <= P <= 0.35. We show that the dependence of the thermal conductivity of the sintered tungsten samples on the porosity shows a critical behaviour. A theoretical explanation of this behaviour and a predictive model for this porosity dependence are proposed

Thermal transport properties of halide solid solutions: Experiments vs equilibrium molecular dynamics

The composition dependence of thermal transport properties of the (Na,K)Cl rocksalt solid solution is investigated through equilibrium molecular dynamics (EMD) simulations in the entire range of composition and the results are compared with experiments published in recent work [Gheribi et al., J. Chem. phys. 141, 104508 (2014)]. The thermal diffusivity of the (Na,K)Cl solid solution has been measured from 473 K to 823 K using the laser flash technique, and the thermal conductivity was deduced from critically assessed data of heat capacity and density. The thermal conductivity was also predicted at 900 K in the entire range of composition by a series of EMD simulations in both NPT and NVT statistical ensembles using the Green-Kubo theory. The aim of the present paper is to provide an objective analysis of the capability of EMD simulations in predicting the composition dependence of the thermal transport properties of halide solid solutions. According to the Klemens-Callaway [P. G. Klemens, Phys. Rev. 119, 507 (1960) and J. Callaway and H. C. von Bayer, Phys. Rev. 120, 1149 (1960)] theory, the thermal conductivity degradation of the solid solution is explained by mass and strain field fluctuations upon the phonon scattering cross section. A rigorous analysis of the consistency between the theoretical approach and the EMD simulations is discussed in detail.

Thermal conductivity of halide solid solutions: measurement and prediction.

The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed.