Journal Article

PUBDB-2015-00599

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Absorption kinetics and hydride formation in magnesium films: Effect of driving force revisited

Uchida, H. T. (Corresponding Author)>Extern* ; Wagner, S.>Extern* ; Hamm, M.>Extern* ; Kürschner, J.>Extern* ; Kirchheim, R. ; Hjörvarsson, B. ; Pundt, A.>Extern*

2015
Elsevier Science Amsterdam [u.a.]

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Please use a persistent id in citations: doi:10.1016/j.actamat.2014.11.031

Abstract: Electrochemical hydrogen permeation measurements and in situ gas-loading X-ray diffraction measurements were performed on polycrystalline Mg films. Hydrogen diffusion constants, the hydride volume content and the in-plane stress were determined for different values of driving forces at 300 K. For α-Mg–H, a hydrogen diffusion constant of View the MathML sourceDHMg=7(±2)·10-11 m2 s−1 was determined. For higher concentrations, different kinetic regimes with reduced apparent diffusion constants View the MathML sourceDHtot were found, depending on the driving force, decreasing to about View the MathML sourceDHtot = 10−18 m2 s−1. This lowest measured diffusion constant is two orders of magnitude larger than that of bulk β-MgH2, and the difference is ascribed to a contribution from a fast diffusion along grain boundaries. The different kinetics regimes are attributed to the spatial distribution of hydrides. A heterogeneous hydride nucleation and growth model is suggested that is based on hemispherical hydrides spatially distributed according to the nuclei densities expressed as a function of the driving force. The model allows us to qualitatively explain the complex stress development, the different diffusion regimes and the blocking-layer thickness. As the blocking-layer thickness inversely scales with the driving force, small driving forces allow the hydriding of large film volume fractions. Maximum stress situations occur for hydride distances reaching four times the hydride radius and for hydride distances equaling the film thickness.

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Contributing Institute(s):

1. DOOR-User (DOOR)

Research Program(s):

1. 6G3 - PETRA III (POF3-622) (POF3-622)
2. FS-Proposal: II-20100323 EC (II-20100323-EC) (II-20100323-EC)
3. FS-Proposal: I-20120283 (I-20120283) (I-20120283)

Experiment(s):

1. DORIS Beamline B2 (DORIS III)
2. PETRA Beamline P08 (PETRA III)

Appears in the scientific report 2015

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Database coverage:
; Current Contents - Engineering, Computing and Technology ; Current Contents - Physical, Chemical and Earth Sciences ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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