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Pseudo-Binary Phase Diagram of LiNH₂-MH (M = Na, K) Eutectic Mixture.

ABSTRACT: The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH₂) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH₂ with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH₂ combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH₂. This lower temperature operation of both LiNH₂-NaH and LiNH₂-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH₂-0.85NaH and 0.25LiNH₂-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon.

SUBMITTER: Pathak P

PROVIDER: S-EPMC9268627 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The intriguing functional nature of ceramics containing rare earth sesquioxide (RES) is associated with the type of polymorphic structure they crystallize into. They prefer to be in the cubic, monoclinic or hexagonal structure in the increasing order of cation size, RRE. Since the functional properties of these ceramics varies with RRE, temperature and pressure, a systematic investigation delineating the cation size effect is indispensable. In the present work we report the structural stability and compressibility behaviour of the RES ceramics, (Eu1-xLax)2O3, of RESs with dissimilar structure and significant difference in cationic radii. The selected compositions of (Eu1-xLax)2O3 have been studied using the in-situ high pressure synchrotron X-ray diffraction and the structural parameters obtained through Rietveld refinement. The cubic structure, which is stable for 0.95 Å [Formula: see text] RRE [Formula: see text] Å at ambient temperature and pressure (ATP), prefers a cubic to hexagonal transition at high pressures. The biphasic region of cubic and monoclinic structure, which is stable for 0.98 Å [Formula: see text] RRE [Formula: see text] Å at ATP, prefers a cubic/monoclinic to hexagonal transition at high pressures. Further, in the biphasic region of monoclinic and hexagonal structure, observed for 1.025 Å [Formula: see text]RRE [Formula: see text] Å, the monoclinic phase is found to be progressing towards the hexagonal phase with increasing pressure. The pure hexagonal phase obtained for 1.055 Å [Formula: see text] RRE [Formula: see text] 1.10 Å is found to be structurally stable at high pressures. The bulk moduli are obtained from the Birch-Murnaghan equation of state fit to the compressibility data and its dependance on the cation size is discussed. The microstrain induced by the difference in cation size causes an internal pressure in the crystal structure leading to a reduction in the bulk modulus of [Formula: see text] and 0.6. A pressure-concentration (P-x) phase diagram upto a pressure of 25 GPa is constructed for (Eu1-xLax)2O3. This would provide an insight to the fundamental and technological aspects of these materials and the RESs in general.

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Pseudo-Binary Phase Diagram of LiNH₂-MH (M = Na, K) Eutectic Mixture.

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Pseudo-Binary Phase Diagram of LiNH2-MH (M = Na, K) Eutectic Mixture.

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Pseudo-Binary Phase Diagram of LiNH₂-MH (M = Na, K) Eutectic Mixture.