Thermodynamic Modeling of Hydrogen Storage Capacity in Mg-Na Alloys
Thermodynamic modeling of the H-Mg-Na system is performed for the first time in this work in order to understand the phase relationships in this system. A new thermodynamic description of the stable NaMgH3 hydride is performed and the thermodynamic models for the H-Mg, Mg-Na, and H-Na systems are reassessed using the modified quasichemical model for the liquid phase. The thermodynamic properties of the ternary system are estimated from the models of the binary systems and the ternary compound using CALPHAD technique. The constructed database is successfully used to reproduce the pressure-composition isotherms for MgH2 + 10 wt.% NaH mixtures. Also, the pressure-temperature equilibrium diagram and reaction paths for the same composition are predicted at different temperatures and pressures. Even though it is proved that H-Mg-Na does not meet the DOE hydrogen storage requirements for onboard applications, the best working temperatures and pressures to benefit from its full catalytic role are given. Also, the present database can be used for thermodynamic assessments of higher order systems.
Understanding the hydrogen storage behavior of promising Al–Mg–Na compositions using thermodynamic modeling
Thermodynamic modeling of the Al–Mg–Na–H system is performed in this work to understand the phase relationships and reaction mechanisms in this system. The Al–Na system is reassessed using the modified quasichemical model for the liquid phase. All the terminal solid solutions were remodeled using the compound energy formalism. The thermodynamic properties of the ternary systems are estimated from the models of the binary systems and the ternary compound using the CALPHAD method. The reaction pathways for the systems MgH2/AlH3, MgH2/NaAlH4, and MgH2/Na3AlH6 are calculated and compared to the experimental data from the literature. Details about the reaction mechanisms and temperatures, the amount of the products, and their composition are revealed and discussed in this work. The calculations show that in the composites MgH2/NaAlH4 and MgH2/Na3AlH6, the components spontaneously destabilize mutually in specific relative amounts by forming NaMgH3, which may play only a catalytic role on the decomposition of (MgH2 + Al) mixture, NaAlH4, or Na3AlH6. Also, Al destabilizes MgH2 and NaMgH3 by forming β phase and reducing the decomposition temperatures of these hydrides by more than 50 °C. The constructed database is successfully used to reproduce the pressure–composition isotherms (PCIs) for Mg-10 at% Al and Mg-4 at% Al alloys at 350 °C. The results provide a better understanding of the reaction mechanisms in the PCIs found in the literature concerning the number of plateau pressures and their sloping. It is shown that the first plateau pressure observed during the PCIs of Al–Mg alloys depends on Al content and is higher than that of pure Mg. This difference is due to Al solubility in hcp-Mg.
Use of a specific antiserum for renin detection in human kidney.
The use of anti-human renin antibodies made possible the intrarenal localization of renin in human kidney by immunofluorescence. In normal kidney, only some juxtaglomerular apparatus (JGA) were fluorescent. In these JGA, granular or diffuse fluorescence was only seen in afferent arterioles and was not present in all cells. In the ischemic areas of partially infarcted kidney, fluorescence was seen in all JGA and in interlobular arteries. In these arteries the most eccentric cells were often the most positive. In the nonischemic areas of the same kidneys, fluorescence was not seen in JGA, but was observed in proximal tubular cells, suggesting the reabsorption of filtered renin at this site.