Structural evolution upon decomposition of the LiAlH4 + LiBH4 system

In the present work we focus the attention on the phase structural transformations occurring upon the
desorption process of the LiBH4 + LiAlH4 system. This study is conducted by means of manometric–
calorimetric, in situ Synchrotron Radiation Powder X-ray Diffraction (SR-PXD) and ex situ Solid State
Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) measurements. The desorption reaction
is characterized by two main dehydrogenation steps starting at 320 and 380 C, respectively. The first
step corresponds to the decomposition of LiAlH4 into Al and H2 via the formation of Li3AlH6 whereas
the second one refers to the dehydrogenation of LiBH4 (molten state). In the range 328–380 C, the molten
LiBH4 reacts with metallic Al releasing hydrogen and forming an unidentified phase which appears to
be an important intermediate for the desorption mechanism of LiBH4–Al-based systems. Interestingly,
NMR studies indicate that the unknown intermediate is stable up to 400 C and it is mainly composed
of Li, B, Al and H. In addition, the NMR measurements of the annealed powders (400 C) confirm that
the desorption reaction of the LiBH4 + Al system proceeds via an amorphous boron compound