H2 Isotherms and Diffusion Parameters of H in fcc Pd–Mg Alloys

Hydrogen isotherms, p H2 -H content relationships, have been obtained for fcc Pd–Mg alloys. One set of alloy compositions was employed for isotherm measurements from 273 to 343 K and another set of compositions was employed for isotherms from 423 to 523 K. It is shown in this work from X-ray diffrac...

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Published inJournal of physical chemistry. C Vol. 117; no. 2; pp. 1071 - 1080
Main Authors Wang, Da, Flanagan, Ted B
Format Journal Article
LanguageEnglish
Published Columbus, OH American Chemical Society 17.01.2013
Subjects
Applied sciences
Chemical and electrochemical properties
Exact sciences and technology
Metals. Metallurgy
FCC lattices
Hydrogen
Adsorption isotherm
Solubility
Dilute alloy
Palladium alloy
Impurity trapping
X ray diffraction
Internal oxidation
Magnesium addition
Nano precipitate
Impurity diffusion
Chemical composition
Activation energy
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Summary:Hydrogen isotherms, p H2 -H content relationships, have been obtained for fcc Pd–Mg alloys. One set of alloy compositions was employed for isotherm measurements from 273 to 343 K and another set of compositions was employed for isotherms from 423 to 523 K. It is shown in this work from X-ray diffraction that Mg expands the fcc Pd lattice. In the dilute phase at a given low p H2 the H2 solubility increases with atom fraction Mg, X Mg, which is expected for alloys with expanded lattices relative to Pd. Thermodynamic parameters for H2 solution have been obtained from the isotherms. Diffusion parameters have been determined from the H fluxes through Pd–Mg alloy membranes. The dependence of Fick’s diffusion constants, D H, on the H content at the upstream side of the membrane has been determined. The diffusion constants decrease with increase in X Mg. The activation energies for diffusion have been determined for three membranes with different Mg contents and these increase with X Mg. Internal oxidation of Pd–Mg alloys results in nanosized MgO precipitates within a Pd matrix. H2 solubilities (323 K) have been measured for several internally oxidized alloys, and these indicate trapping at or near the Pd/MgO interfaces. Partially internally oxidized Pd–Mg alloy membranes are shown to have a greater resistance to CO poisoning than Pd membranes.
ISSN:1932-7447
1932-7455
DOI:10.1021/jp310978y