Herzogenrath, Germany
Herzogenrath, Germany

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Wu G.,Jülich Research Center | Yazhenskikh E.,Jülich Research Center | Hack K.,GTT Technologies | Muller M.,Jülich Research Center
Fuel Processing Technology | Year: 2015

The viscosity model recently developed for fully liquid pure oxides and binary systems is extended to describe the viscosity of multicomponent systems, based on the thermodynamic modified associate species model. In the model the viscosity is linked to the distribution of associate species as well as the connectivity of associate species. To describe the viscosity for multicomponent systems, the ternary associate species are introduced. The focus of the present paper is to describe the viscosity of the system SiO2-Al2O3-CaO-MgO-Na2O-K2O and its ternary or higher order subsystems. The model shows a good performance in describing the viscosity using only one set of model parameters, which all have a clear physico-chemical meaning. The viscosity behavior when substituting one network modifier for another at constant SiO2 contents is well described. The Al2O3-induced viscosity maximum is also well described, in which the position and magnitude of the viscosity maximum as a function of composition and temperature (charge compensation effect) are properly predicted. Another viscosity maximum when replacing Al2O3 with SiO2 for constant contents of the network modifiers is well presented. Moreover, the current model is self-consistent, in which the extension of viscosities from lower order systems to higher order systems works well, and vice versa. © 2015 Elsevier B.V.

Sergeev D.,Jülich Research Center | Yazhenskikh E.,Jülich Research Center | Talukder N.,Jülich Research Center | Kobertz D.,Jülich Research Center | And 2 more authors.
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2016

Thermodynamic properties of the reciprocal NaCl-KCl-NaNO3-KNO3 system are of interest for selecting compositions, which can be used as phase change materials in thermal energy storage. In the presented work two mixtures 7.5KCl-92.5NaNO3 and 12.5NaCl-87.5KNO3 on the diagonal sections of the reciprocal system with the liquidus temperatures of 549 K and 561 K, respectively were studied by DSC and DROP calorimetry. The heat capacities and the enthalpy increments of the solid and the liquid phases were obtained for both mixtures (ΔH549 K=9.5 kJ/mol, ΔH514-549 K=16.9 kJ/mol, ΔH519-561 K=17.0 kJ/mol). The combination of these results allows the calculation of the phase transition enthalpies. DROP-calorimeter was used in a mode of slow heating rate (0.5 K/min) thermal analysis, where the DROP-calorimetric detector was applied for the direct determination of phase transition enthalpies. The thermodynamic properties were calculated using our own dataset of the reciprocal system. The analysis of our experimental and calculated results of enthalpy increments and heat capacities has confirmed that our dataset can be used for prediction of thermodynamic properties of the full reciprocal system. Based on this conclusion three additional compositions 50NaNO3-5.5KCl-44.5KNO3, 28NaNO3-12.4KCl-59.6KNO3 and 13.1NaNO3-11.2KCl-75.7KNO3 of the system with liquidus temperatures at 481 K, 510 K, and 549 K were suggested as potential phase change materials (ΔH481 K=9.8 kJ/mol, ΔH496-510 K=12.7 kJ/mol and ΔH510-549 K=15.8 kJ/mol). © 2016 Elsevier Ltd. All rights reserved.

Sergeev D.,Jülich Research Center | Yazhenskikh E.,Jülich Research Center | Kobertz D.,Jülich Research Center | Hack K.,GTT Technologies | Muller M.,Jülich Research Center
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2015

Differential thermal analysis of the various compositions in the KCl-NaNO3 and NaCl-KNO3 systems has been performed. Temperatures of phase transitions were obtained. The relative content of NaCl, KCl, NaNO3, and KNO3 compounds was determined by the use of X-ray diffraction analysis. These results together with the experimental data from literature were used for optimization of thermodynamic parameters for all available phases and compounds to obtain the Gibbs energy dataset which can be used for the calculation and prediction of the phase diagrams and other thermodynamic properties of these systems. © 2015 Elsevier Ltd. All rights reserved.

Wu G.,Jülich Research Center | Yazhenskikh E.,Jülich Research Center | Hack K.,GTT Technologies | Wosch E.,RWTH Aachen | Muller M.,Jülich Research Center
Fuel Processing Technology | Year: 2015

Slag viscosity as a function of temperature and composition is a very important factor in determining the operating temperature, blended coals as well as fluxing agents for slagging gasification. A number of models for predicting the viscosity of fuel slags have been developed, however, most of them are only valid in a limited range of temperatures and compositions. This study aims at developing a new viscosity model for fully liquid slag systems in the Newtonian range, based on the thermodynamic modified associate species model. The viscosity model is a structurally-based model, which gives a reliable prediction over the whole range of compositions and a broad range of temperatures. The focus of the present paper is to collect and model the experimental data for pure oxides SiO2, Al2O3, CaO, MgO, Na2O, K2O and binary systems SiO2-Al2O3, SiO2-CaO, SiO2-MgO, SiO2-Na2O, SiO2-K2O, Al2O3-CaO, Al2O3-MgO, Al2O3-Na2O, Al2O3-K2O, which is the first step to develop a new viscosity model for the system SiO2-Al2O3-CaO-MgO-Na2O-K2O. A good agreement between experimental data and calculated data has been achieved using only one set of model parameters, which have a clear physico-chemical meaning. Moreover, the extrapolated viscosities to the regions where no experimental data are available in literature are reasonable. © 2015 Elsevier B.V.

PubMed | GTT Technologies, University of California at Los Angeles and RWTH Aachen
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2016

We assess the concept of alchemical transformations for predicting how a further and not-tested change in composition would change materials properties. This might help to guide ab initio calculations through multidimensional property-composition spaces. Equilibrium volumes, bulk moduli, and relative lattice stability of fcc and bcc 4d transition metals Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag are calculated using density functional theory. Alchemical derivatives predict qualitative trends in lattice stability while equilibrium volumes and bulk moduli are predicted with less than 9% and 28% deviation, respectively. Predicted changes in equilibrium volume and bulk moduli for binary and ternary mixtures of Rh-Pd-Ag are in qualitative agreement even for predicted bulk modulus changes as large as +100% or -50%. Based on these results, it is suggested that alchemical transformations could be meaningful for enhanced sampling in the context of virtual high-throughput materials screening projects.

Loffler A.,Friedrich - Schiller University of Jena | Hack K.,GTT Technologies | Rettenmayr M.,Friedrich - Schiller University of Jena
International Journal of Materials Research | Year: 2010

Recent developments in modeling the interaction of thermodynamics and kinetics during microsegregation formation in multicomponent alloys are reported. A model accounting for solid state back diffusion, dendrite arm coarsening, dendrite tip undercooling, eutectic undercooling and thermodynamic correction of the interface concentrations is presented. By coupling the solution of the diffusion equation in the liquid and solid phases with the thermochemistry library ChemApp, the phase equilibria at the solid-liquid interface are calculated at each time step. Using an activity based method for identifying multiphase equilibria and metastable extensions of the stability range of phases, a thermodynamically consistent implementation of eutectic undercooling in multicomponent systems is achieved. The model is equipped with a userfriendly interface that allows setting the model parameters interactively and that presents the results (solute distribution, phase fractions, secondary arm spacing) in a pertinent way. © Carl Hanser Verlag GmbH & Co. KG.

Saxena S.K.,Florida International University | Eriksson G.,GTT Technologies
Journal of Physics and Chemistry of Solids | Year: 2015

A thermodynamic database on all iron phases (BCC, FCC, HCP and melt) has been created using thermochemical and equations of state data from experiments and theory. The database permits the calculation of the phase diagram of iron to physical conditions of the Earth's core (pressure of 365. GPa and temperature of 6453. K). If the inner core were all iron, its upper temperature would be 6453 (500). K. The average heat capacity of a pure iron HCP inner core is calculated as 29.4. J/mol/K with an entropy of 92. J/mol/K and a gruneisen parameter of 1.81. © 2015 Elsevier Ltd.

Eriksson G.,GTT Technologies | Bale C.W.,Ecole Polytechnique de Montréal | Pelton A.D.,Ecole Polytechnique de Montréal
Journal of Chemical Thermodynamics | Year: 2013

The first-melting projection of the phase diagram of a ternary or higher-order system shows the temperature at which a liquid phase first appears upon heating at any given composition in a system at thermodynamic equilibrium. In most systems, first-melting projections are identical to solidus projections. It is shown that they obey the same well-known topological rules as isothermal sections of phase diagrams. Hence, their interpretation is straightforward. Only in systems with catatectic invariants or retrograde solid solubility do exceptions to these rules occur, and then only over limited composition regions. In these regions the first-melting and solidus projections are not identical. In such cases it is preferable to plot the first-melting projection which is always single-valued at all compositions. A general algorithm for calculating first-melting projections thermodynamically is outlined. © 2013 Elsevier Ltd. All rights reserved.

Ouzilleau P.,Ecole Polytechnique de Montréal | Gheribi A.E.,Ecole Polytechnique de Montréal | Eriksson G.,GTT Technologies | Lindberg D.K.,Åbo Akademi University | Chartrand P.,Ecole Polytechnique de Montréal
Carbon | Year: 2015

The development is presented of a model of the thermodynamic functions of enthalpy, entropy and Gibbs energy for the elements carbon and hydrogen in coke crystallites. It is applicable to varying degrees of graphitization, described by the crystallite length La and the crystallite height Lc. The model parameters are derived from known properties such as bond enthalpies and entropies of formation. Good agreement has been obtained between the predicted thermal dehydrogenation of petroleum cokes and experimental data. The removal of hydrogen from idealized coke crystallites is predicted to occur mostly between 1100 and 1300 K. Agreement has also been found in the comparison of the predicted thermodynamic stability of coke relative to graphite, in a previous experimental study. This stability has been determined as at ≈900 J g-1 at temperatures between 950 and 1250 K and for La = 10 nm. The current predictive capacity of the present model is valid for temperatures up to 2500 K. © 2014 Elsevier Ltd. All rights reserved.

Harvey J.-P.,Ecole Polytechnique de Montréal | Eriksson G.,GTT Technologies | Orban D.,Ecole Polytechnique de Montréal | Chartrand P.,Ecole Polytechnique de Montréal
American Journal of Science | Year: 2013

We present in this paper a robust strategy to determine the equilibrium state, in the isobaric-isothermal (NPT) ensemble, of complex multicomponent systems in which solid solutions presenting order/disorder transitions are stable. The algorithm specifically designed to construct the first estimate of the phase assemblage describing the equilibrium state of the system is presented in detail in this work and tested on different binary and ternary systems in which solid solutions are modeled using i) the cluster site approximation or ii) the cluster variation method in the tetrahedron approximation for both the face-centered and body-centered cubic solutions. The performance of the sequential quadratic strategy using an exact Newton method and a linesearch method, implemented in this work for the specific resolution of Gibbs free energy minimization problems, is compared to the one of other large-scale optimization software packages: SNOPT, IPOPT, and KNITRO. Key subroutines implemented in the strategy to locate local minima, and specifically implemented to improve the convergence toward targeted local minima, are also presented in this work and highlight the robustness of our approach.

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