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

In English

Författare

  • Gagik Barkhordarian
  • Torben R Jensen
  • Stefania Doppiu
  • Ulrike Boesenberg
  • Andreas Borgschulte
  • Robin Gremaud
  • Yngve Cerenius
  • Martin Dornheim
  • Thomas Klassen
  • Ruediger Bormann

Summary, in English

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.

Publiceringsår

2008

Språk

Engelska

Sidor

2743-2749

Publikation/Tidskrift/Serie

Journal of Physical Chemistry C

Volym

112

Issue

7

Dokumenttyp

Artikel i tidskrift

Förlag

The American Chemical Society (ACS)

Ämne

  • Natural Sciences
  • Physical Sciences

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 1932-7447