Transmission electron microscopic observations of the decomposition process of lithium alanate

The thermal decomposition process of lithium alanate (LiAlH₄) was investigated by TEM, TG-DTA and XRD. It was shown that LiAlH₄ decomposes through a two-step reaction: a liquid-to-solid phase transition in the first step of the decomposition and a solid-to-solid reaction in the second step of the decomposition, both steps accompanied by hydrogen release. The particle size of the aluminum (Al), which formed in the first decomposition step, was much larger than that in the second decomposition step. In addition, Al particles formed in the liquid phase of LiAlH₄ in the first decomposition step, while, they form in solid phase of Li₃AlH₆ in the second decomposition step, resulting in the kinetics of the first decomposition step being faster than that of the second decomposition step. The investigation clearly demonstrated the reaction model of the decomposition of LiAlH₄ in the nano-scale, showing different diffusion processes of Al in each of the decomposition steps.