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Sergeev D.,Julich Research Center | Yazhenskikh E.,Julich Research Center | Kobertz D.,Julich Research Center | Hack K.,GTT Technologies | Muller M.,Julich 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. Source

Sergeev D.,Julich Research Center | Yazhenskikh E.,Julich Research Center | Talukder N.,Julich Research Center | Kobertz D.,Julich 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. Source

Eriksson G.,GTT Technologies | Bale C.W.,Ecole Polytechnique de Montreal | Pelton A.D.,Ecole Polytechnique de Montreal
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. Source

Wu G.,Julich Research Center | Seebold S.,Julich Research Center | Yazhenskikh E.,Julich Research Center | Hack K.,GTT Technologies | Priv-Doz M.M.,Julich Research Center
32nd Annual International Pittsburgh Coal Conference: Coal - Energy, Environment and Sustainable Development, IPCC 2015 | Year: 2015

IGCC power plants have high efficiency and represent a good opportunity to control the CO2 emissions produced from the use of fossil fuels such as coal. The core of an IGCC power plant is the gasifier, in which slag viscosity as a function of temperature and composition plays a significant role in determining the optimum operating conditions. Many processes during gasification are related to the slag viscosity, such as particle sticking (or droplet sticking), slag flow and slag tapping. However, most of the previous viscosity models are only valid in a limited range of temperatures and compositions resulting from the lack of an effective description of the structural dependence of the viscosity. In this study, a structure based model has been developed for the fully liquid system SiO2-Al2O3-CaO-MgO-Na2O-K2O-FeO-Fe2O3 and its subsystems in the Newtonian range, based on the thermodynamic modified associate species model. To obtain an effective structural dependence of the viscosity, it is linked to the associate species distribution and the connectivity of associate species. Using this principle, both the temperature- and composition-induced structural changes of oxide melts can be described by a set of monomeric associate species in combination with the critical clusters induced by self- and inter-polymerization. With the new model, one of the challenges of the viscosity behavior in SiO2-based binary systems, the so-called lubricant effect, is well described. The viscosity behavior when substituting one network modifier for another at constant SiO2 content is also well described. The Al2O3-induced viscosity maximum is also described, in which the position and magnitude of the viscosity maximum as a function of temperature and composition (charge compensation effect) are properly predicted. The new model is self-consistent and gives a reliable prediction over the whole range of compositions and a broad range of temperatures using only one set of model parameters, which all have a clear physico-chemical meaning. In addition, the iso-viscosity lines and 3-dimensional viscosity surfaces are generated and further applied to determine the effects of coal ash fluxing and blending. Source

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. Source

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