Formation of Ca(BH4)2 from Hydrogenation of CaH2+MgB2 Composite
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- 作者：Gagik Barkhordarian ; Torben R. Jensen ; Stefania Doppiu ; Ulrike Bö ; senberg ; Andreas Borgschulte ; Robin Gremaud ; Yngve Cerenius ; Martin Dornheim ; Thomas Klassen ; Rü ; diger Bormann
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：February 21, 2008
- 年：2008
- 卷：112
- 期：7
- 页码：2743 - 2749
- 全文大小：269K
- 年卷期：v.112,no.7(February 21, 2008)
- ISSN：1932-7455
文摘
The hydrogenation of the CaH2+MgB2 composite and the dehydrogenation of the resulting products areinvestigated in detail by in situ time-resolved synchrotron radiation powder X-ray diffraction, high-pressuredifferential scanning calorimetry, infrared, and thermovolumetric measurements. It is demonstrated that aCa(BH4)2+MgH2 composite is formed by hydrogenating a CaH2+MgB2 composite, at 350 
C and 140 bar ofhydrogen. Two phases of Ca(BH4)2 were characterized: 
- and 
-Ca(BH4)2. -Ca(BH4)2 transforms to -Ca(BH4)2 at about 130 C. Under the conditions used in the present study, -Ca(BH4)2 decomposes first toCaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at 360 C, beforecomplete decomposition to CaH2, Mg, B (or MgB2), and hydrogen at 400 C. During hydrogenation under140 bar of hydrogen, -Ca(BH4)2 is formed at 250 C, and -Ca(BH4)2 is formed when the sample is cooledto less than 130 C. Ti isopropoxide improves the kinetics of the reactions, during both hydrogenation anddehydrogenation. The dehydrogenation temperature decreases to 250 C, with 1 wt % of this additive, andhydrogenation starts already at 200 C. We propose that the improved kinetics of the above reactions withMgB2 (compared to pure boron) can be explained by the different boron bonding within the crystal structureof MgB2 and pure boron.
C and 140 bar ofhydrogen. Two phases of Ca(BH4)2 were characterized: - and -Ca(BH4)2. -Ca(BH4)2 transforms to -Ca(BH4)2 at about 130 C. Under the conditions used in the present study, -Ca(BH4)2 decomposes first toCaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at 360 C, beforecomplete decomposition to CaH2, Mg, B (or MgB2), and hydrogen at 400 C. During hydrogenation under140 bar of hydrogen, -Ca(BH4)2 is formed at 250 C, and -Ca(BH4)2 is formed when the sample is cooledto less than 130 C. Ti isopropoxide improves the kinetics of the reactions, during both hydrogenation anddehydrogenation. The dehydrogenation temperature decreases to 250 C, with 1 wt % of this additive, andhydrogenation starts already at 200 C. We propose that the improved kinetics of the above reactions withMgB2 (compared to pure boron) can be explained by the different boron bonding within the crystal structureof MgB2 and pure boron.