Differential scanning calorimetry (DSC) and synchrotron X-ray diffraction study of unmilled and milled LiBH4: A partial release of hydrogen at moderate temperatures

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. © 2011 by the authors; licensee MDPI, Basel, Switzerland.