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Hydrogenation of Magnesium Nanoblades: The Effect of Concentration Dependent Hydrogen Diffusion

[+] Author Affiliations
Bo Yang

University of Texas at Arlington, Arlington, TX

Yuping He, Yiping Zhao

University of Georgia, Athens, GA

Paper No. IMECE2011-64466, pp. 585-591; 7 pages
doi:10.1115/IMECE2011-64466
From:
  • ASME 2011 International Mechanical Engineering Congress and Exposition
  • Volume 4: Energy Systems Analysis, Thermodynamics and Sustainability; Combustion Science and Engineering; Nanoengineering for Energy, Parts A and B
  • Denver, Colorado, USA, November 11–17, 2011
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-5490-7
  • Copyright © 2011 by ASME

abstract

By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on H concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. Thus, as it proceeds, the hydrogenation process gradually changes from surface reaction-limited to diffusion-limited. In both one- and two-dimensional simulations, it is shown that a hydride shell is not formed during hydrogenation. In contrast, a hydride core is formed during dehydrogenation. The strong (exponential) concentration dependence of H diffusion coefficient throws profound influence on the stability and instability of a diffusion front, i.e., a H diffusion front in hydrogenation, and a H-vacancy diffusion front in dehydrogenation. In the latter case, the front tends to corrugate forming islands when the H2 release rate is high.

Copyright © 2011 by ASME

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