Differential Scanning Calorimetry (DSC) and Synchrotron X-ray Diffraction Study of Unmilled and Milled LiBH₄: A Partial Release of Hydrogen at Moderate Temperatures

Author： Lang J. Gerhauser A. Filinchuk Y. Klassen T. Huot J.

Publisher： MDPI

E-ISSN： 2073-4352|2|1|1-21

ISSN： 2073-4352

Source： Crystals, Vol.2, Iss.1, 2011-12, pp. : 1-21

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Abstract

A systematic investigation of phase transitions in unmilled and milled LiBH₄ has been performed by Pressurized Differential Scanning Calorimetry (PDSC). It was found that a large exotherm is present below the low temperature (LT) → high temperature (HT) phase transition. This exotherm is not caused by air contamination but seems to originate from hydrogen release from a solid solution in the matrix of LiBH₄ low temperature phase. The exotherm activation energy has been measured to be 100 kJ mol^-1. Calorimetric measurements under argon and hydrogen have shown that for the milled sample, the endothermic peak of the LT → HT transition is split in two when the PDSC scan is performed under hydrogen atmosphere. Synchrotron X-ray powder diffraction on the milled LiBH₄ sample revealed only a single-step transition from the LT to HT phase, both under vacuum and under 2 and 40 bar of hydrogen pressure. The axial ratios for the LT LiBH₄ below 300 K are significantly altered by milling; they are also considerably different under 40 bar of hydrogen, indicating an interaction between the hydrogen gas and the LT LiBH₄ solid phase.