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Thermal energy storage (TES) based on molten salts has been identified as a key player in the transition from fossil fuels to renewable energy sources. Solar Salt, a mixture of NaNO3 (60 wt%) and KNO3 (40 wt%), is currently the most advanced heat transfer and storage material used in concentrating solar power (CSP) plants. Here, it is utilized to produce electricity via a Rankine cycle, with steam temperatures reaching 550 °C. The goal of this study is to increase the operating temperature of solar salt to over 600 °C, allowing it to be adapted for use in high-temperature Rankine cycles with steam temperatures greater than 600 °C. Yet, this goal is impaired by the lack of available thermodynamic data given the salt's complex high-temperature decomposition and corrosion chemistry. The study explores the thermodynamics of the decomposition reactions in solar salt, with a focus on suppressing decomposition into corrosive oxide ions up to a temperature of 620 °C. The results provide a new understanding of the stabilization of solar salt at previously unexplored temperatures with effective utilization of gas management techniques. [ABSTRACT FROM AUTHOR]

The amides Na3RE(NH2)6 have been obtained from the metals in supercritical ammonia under ammonobasic conditions at 573 K and 70 MPa for RE = La–Nd, and at 473 K and 40 MPa for RE = Er, Yb. All compounds are formed in the hot zone within a temperature gradient, indicating a retrograde solubility under the applied process conditions. These amides represent soluble intermediates in ammonothermal binary rare earth metal nitride synthesis. All compounds were obtained as microcrystalline powders, while single crystals of those amides containing the heavier rare earth metals could be isolated. The crystal structures were solved and refined from single-crystal and powder X-ray diffraction intensity data. The results of vibrational spectroscopy are reported. Thermal analysis measurements under inert gas atmosphere demonstrated a decomposition to the respective black binary rare earth metal nitrides REN1−δ. [ABSTRACT FROM AUTHOR]

Polycrystalline powder and single crystals of Na2[Zn(NH2)4] ⋅ (NH3)0.24 and Na2[Zn(NH2)4] ⋅ (H2O)0.37 were obtained under ammonobasic conditions at 823 K and 200 MPa. Upon substituting the constituent ammonia by water, the space group (C2/c) and crystal structure remain generally unchanged. Nevertheless, the presence of water during the ammonothermal synthesis has a fundamental impact on the transport direction, changing from exothermic for the pure ammonia system to an endothermic material transport for the hydrate formation under essentially the same experimental conditions. That indicates that even a small amount of oxygen can have a fundamental influence on the solubility and its temperature dependence of dissolved species during ammonobasic synthesis. Chemical analysis, Raman spectroscopy and thermal analysis consistently support the composition assignment. Solid‐state NMR measurements back up the exchange of exclusively ammonia by water, rather than introduction of hydroxide ions. A minor enhancement of the thermal stability of the hydrate compared to the ammoniate is observed. [ABSTRACT FROM AUTHOR]

Polycrystalline powder and single crystals of Na2[Zn(NH2)4] ⋅ (NH3)0.24 and Na2[Zn(NH2)4] ⋅ (H2O)0.37 were obtained under ammonobasic conditions at 823 K and 200 MPa. Upon substituting the constituent ammonia by water, the space group (C2/c) and crystal structure remain generally unchanged. Nevertheless, the presence of water during the ammonothermal synthesis has a fundamental impact on the transport direction, changing from exothermic for the pure ammonia system to an endothermic material transport for the hydrate formation under essentially the same experimental conditions. That indicates that even a small amount of oxygen can have a fundamental influence on the solubility and its temperature dependence of dissolved species during ammonobasic synthesis. Chemical analysis, Raman spectroscopy and thermal analysis consistently support the composition assignment. Solid‐state NMR measurements back up the exchange of exclusively ammonia by water, rather than introduction of hydroxide ions. A minor enhancement of the thermal stability of the hydrate compared to the ammoniate is observed. [ABSTRACT FROM AUTHOR]

Single crystals of Na2La4(NH2)14·NH3 were obtained from supercritical ammonia under ammonobasic conditions at a temperature of 573 K and 120 MPa pressure. It represents a lanthanum-rich intermediate in the ammonothermal synthesis of LaN. Upon aging, the title compound loses the crystal ammonia, resulting in pale crystals of Na2La4(NH2)14, the original space group P212121 being retained in a very similar unit cell. However, the crystal structure reacts to subtle changes in the composition as well as to the modified coordination of particularly the sodium cations interconnecting lanthanum amide layers within a third dimension. Results of Raman spectroscopic studies are reported. The observations of thermal analysis measurements indicating the formation of lanthanum nitride, in combination with the observed retrograde solubility in liquid ammonia, contribute to the knowledge of the ammonothermal crystal growth of lanthanum nitride. [ABSTRACT FROM AUTHOR]