Narrowing of the palladium-hydrogen miscibility gap in nanocrystalline palladium

In situ x-ray-diffraction studies of the hydriding behavior of coarse-grained and nanocrystalline palladium samples at ambient temperature are descibed. A previously observed narrowing of the miscibility gap in nanocrystalline palladium was reproduced. The present results, however, demonstrate that...

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Bibliographic Details
Published in:Physical review. B, Condensed matter Condensed matter, 1993-07, Vol.48 (1), p.84-92
Main Authors: EASTMAN, J. A, THOMPSON, L. J, KESTEL, B. J
Format: Article
Language:English
Subjects:
360102 - Metals & Alloys- Structure & Phase Studies
AMBIENT TEMPERATURE
Applied sciences
CHEMICAL REACTIONS
COHERENT SCATTERING
Condensed matter: structure, mechanical and thermal properties
CRYSTALS
DIAGRAMS
DIFFRACTION
ELEMENTS
ENTHALPY
Equations of state, phase equilibria, and phase transitions
Exact sciences and technology
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGENATION
MATERIALS SCIENCE
METALS
Metals. Metallurgy
MIXING HEAT
PALLADIUM
PHASE DIAGRAMS
PHYSICAL PROPERTIES
Physics
PLATINUM METALS
POLYCRYSTALS
SCATTERING
Solubility, segregation, and mixing
phase separation
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
X-RAY DIFFRACTION
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Summary:In situ x-ray-diffraction studies of the hydriding behavior of coarse-grained and nanocrystalline palladium samples at ambient temperature are descibed. A previously observed narrowing of the miscibility gap in nanocrystalline palladium was reproduced. The present results, however, demonstrate that this change in the palladium-hydrogen phase diagram for nanocrystalline material is not related to an inability to form the hydride phase in highly disordered grain boundary regions as previously proposed. Instead, the entire volume of nanocrystalline samples was observed to transform to [beta]-PdH upon exposure to hydrogen. This behavior indicates that the entropy and/or enthalpy of mixing for the palladium-hydrogen system differs in nanocrystalline and coarse-grained materials. Because of these changes in thermodynamic quantities, the phase boundary of the palladium-hydrogen miscibility gap is predicted to be shifted to lower temperatures for nanocrystalline samples.
ISSN:0163-1829
1095-3795
DOI:10.1103/physrevb.48.84