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Formation of Ca(BH4)(2) from hydrogenation of CaH2+MgB2 composite

Barkhordarian, Gagik; Jensen, Torben R; Doppiu, Stefania; Boesenberg, Ulrike; Borgschulte, Andreas; Gremaud, Robin; Cerenius, Yngve LU ; Dornheim, Martin; Klassen, Thomas and Bormann, Ruediger (2008) In Journal of Physical Chemistry C 112(7). p.2743-2749
Abstract
The hydrogenation of the CaH2+MgB2 Composite and the dehydrogenation of the resulting products are investigated in detail by in situ time-resolved synchrotron radiation powder X-ray diffraction, high-pressure differential scanning calorimetry, infrared, and thermovolumetric measurements. It is demonstrated that a Ca(BH4)(2)+MgH2 composite is formed by hydrogenating a CaH2+MgB2 composite, at 350 degrees C and 140 bar of hydrogen. Two phases of Ca(BH4)(2) were characterized: alpha- and beta-Ca(BH4)(2). alpha-Ca(BH4)(2) transforms to beta-Ca(BH4)(2) at about 130 degrees C. Under the conditions used in the present study, beta-Ca(BH4)(2) decomposes first to CaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at... (More)
The hydrogenation of the CaH2+MgB2 Composite and the dehydrogenation of the resulting products are investigated in detail by in situ time-resolved synchrotron radiation powder X-ray diffraction, high-pressure differential scanning calorimetry, infrared, and thermovolumetric measurements. It is demonstrated that a Ca(BH4)(2)+MgH2 composite is formed by hydrogenating a CaH2+MgB2 composite, at 350 degrees C and 140 bar of hydrogen. Two phases of Ca(BH4)(2) were characterized: alpha- and beta-Ca(BH4)(2). alpha-Ca(BH4)(2) transforms to beta-Ca(BH4)(2) at about 130 degrees C. Under the conditions used in the present study, beta-Ca(BH4)(2) decomposes first to CaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at 360 degrees C, before complete decomposition to CaH2, Mg, B (or MgB2), and hydrogen at 400 degrees C. During hydrogenation under 140 bar of hydrogen, beta-Ca(BH4)(2) is formed at 250 degrees C, and alpha-Ca(BH4)(2) is formed when the sample is cooled to less than 130 degrees C. Ti isopropoxide improves the kinetics of the reactions, during both hydrogenation and dehydrogenation. The dehydrogenation temperature decreases to 250 degrees C, with 1 wt % of this additive, and hydrogenation starts already at 200 degrees C. We propose that the improved kinetics of the above reactions with MgB2 (compared to pure boron) can be explained by the different boron bonding within the crystal structure of MgB2 and pure boron. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry C
volume
112
issue
7
pages
2743 - 2749
publisher
The American Chemical Society
external identifiers
  • wos:000253222200077
  • scopus:39849090034
ISSN
1932-7447
DOI
10.1021/jp076325k
language
English
LU publication?
yes
id
409ae6e8-3067-4c8d-a623-b40afe8b9343 (old id 1196509)
date added to LUP
2008-09-10 11:44:27
date last changed
2017-09-10 03:46:11
@article{409ae6e8-3067-4c8d-a623-b40afe8b9343,
  abstract     = {The hydrogenation of the CaH2+MgB2 Composite and the dehydrogenation of the resulting products are investigated in detail by in situ time-resolved synchrotron radiation powder X-ray diffraction, high-pressure differential scanning calorimetry, infrared, and thermovolumetric measurements. It is demonstrated that a Ca(BH4)(2)+MgH2 composite is formed by hydrogenating a CaH2+MgB2 composite, at 350 degrees C and 140 bar of hydrogen. Two phases of Ca(BH4)(2) were characterized: alpha- and beta-Ca(BH4)(2). alpha-Ca(BH4)(2) transforms to beta-Ca(BH4)(2) at about 130 degrees C. Under the conditions used in the present study, beta-Ca(BH4)(2) decomposes first to CaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at 360 degrees C, before complete decomposition to CaH2, Mg, B (or MgB2), and hydrogen at 400 degrees C. During hydrogenation under 140 bar of hydrogen, beta-Ca(BH4)(2) is formed at 250 degrees C, and alpha-Ca(BH4)(2) is formed when the sample is cooled to less than 130 degrees C. Ti isopropoxide improves the kinetics of the reactions, during both hydrogenation and dehydrogenation. The dehydrogenation temperature decreases to 250 degrees C, with 1 wt % of this additive, and hydrogenation starts already at 200 degrees C. We propose that the improved kinetics of the above reactions with MgB2 (compared to pure boron) can be explained by the different boron bonding within the crystal structure of MgB2 and pure boron.},
  author       = {Barkhordarian, Gagik and Jensen, Torben R and Doppiu, Stefania and Boesenberg, Ulrike and Borgschulte, Andreas and Gremaud, Robin and Cerenius, Yngve and Dornheim, Martin and Klassen, Thomas and Bormann, Ruediger},
  issn         = {1932-7447},
  language     = {eng},
  number       = {7},
  pages        = {2743--2749},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry C},
  title        = {Formation of Ca(BH4)(2) from hydrogenation of CaH2+MgB2 composite},
  url          = {http://dx.doi.org/10.1021/jp076325k},
  volume       = {112},
  year         = {2008},
}