Characterisation of mechanochemically synthesised alane (AlH3) nanoparticles

Abstract

A mechanochemical synthesis process has been used to synthesise alane (AlH3) nanoparticles. The alane is synthesised via a chemical reaction between lithium alanate (LiAlH4) and aluminium chloride (AlCl3) at room temperature within a ball mill and at 77K within a cryogenic mill. The reaction product formed consists of alane nanoparticles embedded within a lithium chloride (LiCl) by-product phase. The LiCl is washed with a solvent resulting in alane nanoparticles which are separated from the by-product phase but are kinetically stabilised by an amorphous particle surface layer. The synthesis of a particular alane structural phase is largely dependent on the milling conditions and two major phases (α, α′) as well as two minor phases (β, γ) have been identified. Ball milling at room temperature can also provide enough energy to allow alane to release hydrogen gas and form aluminium metal nanoparticles. A comparison between XRD and hydrogen desorption results suggest a non-crystalline AlH3 phase is present in the synthesised samples.