The effects of nanonickel additive on the decomposition of complex metal hydride LiAlH4 (lithium alanate)

摘要

High energy ball milling up to at least lh does not lead to the transformation of undoped LiAlH_4 as well as LiAlH_4 doped with n-Ni into Li_3AlH_6. In a DSC test the melting of LiAlH_4 is completely eliminated by the addition of 5 wt% n-Ni incorporated by high energy ball milling. The LiAlH4 + 5 wt% n-Ni system processed by ball milling desorbs ~4.8 wt% H_2 at 120 ℃ within 2000 s. At 120 ℃ within a 5000 s time interval the desorption reaction occurs fully in a solid state in one step according to the following reaction: LiAlH_4 -+ l/3Li3AlH6 + 2/3A1 + H_2. This reaction is completely non-volatile. At 140 "C and higher temperatures the desorption reaction of ball milled LiAlH_4 + 5 wt% n-Ni occurs fully in a solid state most likely in two steps according to the following reactions: (1) LiAlH_4 - l/3Li_3AlH_6 + 2/3A1 + H_2 and (2) l/3Li_3AlH_6 - IiH + 1/3A1 + 0.5H_2. However, XRD patterns after reaction (2) do not show the presence of LiH but instead, they show the presence of LiOH. It is possible that LiH is transformed rapidly into LiOH by a mechanism which is now under investigation. When stored for a long time at room temperature the heavily ball milled LiAlH_4 + 5 wt% n-Ni system gradually degrades losing H_2 capacity.