Thermodynamic Assessment of the NaF-KF-UF4 System

In the Molten Salt Reactor (MSR) concept, metal fluorides are key components of possible fuel and coolant salts. The fast reactor option opens the possibility for alternatives to the Li based matrix salts, avoiding the costly 7Li enrichment and the tritium production from residual 6Li. Such alternatives can be based on NaF and KF as matrix components. In this study, two pseudo-binary phase diagrams of NaF-UF4 and KF-UF4, and the NaF-KF-UF4 pseudo-ternary system were experimentally investigated using Differential Scanning Calorimetry (DSC). The obtained data were used to perform a full thermodynamic assessment of the NaF-KF-UF4 system. The calculated pseudo-ternary eutectic was found at 807 K and a 68.9-7.6-23.5 mol% NaF-KF-UF4 composition. The comprehensive experimental and modelling data obtained in this work provide further extension of the JRCMSD thermodynamic database describing thermodynamic properties of key fuel and coolant salts for the MSR technology.

Optical and Thermal Investigations of New Schiff Base/Ester Systems in Pure and Mixed States

New mesomorphic series, 4-hexadecyloxy phenyl-imino-4′-(3-methoxyphenyl)-4″-alkoxybenzoates (An), were prepared and investigated with different thermal and mesomorphic techniques. The synthesized homologous series constitutes four members that differ from each other in the terminal length of flexible chain (n) attached to phenyl ester moiety, which varies between n = 6, 8, 10, and 12 carbons. A lateral CH3O group is attached to the central benzene ring in the meta position with respect to the ester moiety. Molecular structures of all newly prepared homologues were elucidated via FT-IR, 1H and 13C NMR spectroscopy. Mesomorphic and thermal properties were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and the mesophases identified by polarized optical microscopy (POM). DSC and POM examinations revealed that all members of the present series (An) exhibit a purely enantiotropic nematic (N) phase. Comparative evaluations and binary phase diagrams were established between the present homologues and their corresponding shorter one (Bn). The examination revealed that, the length of the flexible alkoxy chain incorporated into the phenylimino moiety is highly effective on the temperature range and stability of the mesophase observed. With respect to the binary mixtures An/Bn, the exhibited N phase showed to cover the whole composition range with eutectic behavior.

Investigation of the K-Mg-Ca Sulfate System as Part of Monitoring Problematic Phase Formations in Renewable-Energy Power Plants

Besides the widely applied hydropower, wind farms and solar energy, biomass and municipal and industrial waste are increasingly becoming important sources of renewable energy. Nevertheless, fouling, slagging and corrosion associated with the combustion processes of these renewable sources are costly and threaten the long-term operation of power plants. During a high-temperature biomass combustion, alkali metals in the biomass fuel and the ash fusion behavior are the two major contributors to slagging. Ash deposits on superheater tubes that reduce thermal efficiency are often composed of complex combinations of sulfates and chlorides of Ca, Mg, Na, and K. However, thermodynamic databases involving all the sulfates and chlorides that would favor a better understanding and control of the problems in combustion processes related to fouling, slagging and corrosion are not complete. In the present work, thermodynamic properties including solubility limits of some phases and phase mixtures in the K2SO4-(Mg,Ca)SO4 system were reviewed and experimentally investigated. Based on the new and revised thermochemical data, binary phase diagrams of the K2SO4-CaSO4 and K2SO4-MgSO4 systems above 400 °C, which are of interest in the combustion processes of renewable-energy power plants, were optimized.

Phase Boundary Mapping in ZrNiSn Half-Heusler for Enhanced Thermoelectric Performance

The solubility range of interstitial Ni in the ZrNi1+xSn half-Heusler phase is a controversial issue, but it has an impact on the thermoelectric properties. In this study, two isothermal section phase diagrams of the Zr-Ni-Sn ternary system at 973 K and 1173 K were experimentally constructed based on the binary phase diagrams of Zr-Ni, Zr-Sn, and Ni-Sn. The thermodynamic equilibrium phases were obtained after a long time of heating treatment on the raw alloys prepared by levitation melting. Solubilities of x<0.07 at 973 K and x<0.13 at 1173 K were clearly indicated. An intermediate-Heusler phase with a partly filled Ni void was observed, which is believed to be beneficial to the lowered lattice thermal conductivity. The highest ZT value~0.71 at 973 K was obtained for ZrNi1.11Sn1.04. The phase boundary mapping provides an important instruction for the further optimization of ZrNiSn-based materials and other systems.