Dispersion and Integration of Dopants by Mechanical Alloying in Complex Hydrogen Storage Materials
Graham, Dennis D.
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https://hdl.handle.net/2142/82844
Description
Title
Dispersion and Integration of Dopants by Mechanical Alloying in Complex Hydrogen Storage Materials
Author(s)
Graham, Dennis D.
Issue Date
2009
Doctoral Committee Chair(s)
Ian Robertson
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
Prior work had found that MgH2, a thermodynamically hindered system, can be destabilized through the introduction of Si but no microstructural information has been presented. In this work, confirmation of the proposed forward dehydriding mechanism to Mg2Si was obtained in the MgH 2 + Si system using energy dispersive spectroscopy and electron diffraction. In addition, particle sizes were calculated for catalysts added to this system, and electron tomography was applied to determine the three-dimensional catalyst dispersion. In the kinetically hindered Ca(BH4)2 system, initial efforts to synthesize Ca(BH4)2 from CaB 6 in this work were shown to be unsuccessful both structurally and microchemically by using a combination of energy dispersive spectroscopy, electron energy loss spectroscopy, and X-ray diffraction, confirming results obtained via a volumetric Sievert's apparatus that showed no significant reversibility. However, reversibility is achieved if the reaction is started from Ca(BH 4)2. In this work, the degree of mixing of added catalysts to the reversible Ca(BH4)2 system was determined via energy dispersive spectroscopy. In addition, chemical and diffraction analysis of the amorphous intermediate phase indicated no significant segregation occurs on dehydriding. It is concluded from the work reported herein that, in this work that, although ball milling does provide a rapid method for introducing catalysts and for reducing grain size, it can hinder addressing the fundamental question, how the catalyst actually provides catalytic assistance to the material. This work has assisted the search for a viable hydrogen storage material for the automotive industry by addressing gaps in the current understanding regarding kinetic assistance of complex hydrogen storage materials with catalysts on a microstructural level.
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