Structure formation of activated nickel catalyst during caustic leaching of a nickel-aluminium alloy

An activated nickel catalyst (Raney-type nickel) was produced by leaching nickel-aluminium alloys in alkali solution. The structure of this leached residue was investigated using transmission electron microscopy and X-ray diffraction. The leaching process selectively dissolves aluminium from the alloy and the remaining atoms form a nonequilibrium body-centred cubic phase of disordered nickel and aluminium atoms. This phase exists over a wide range of compositions. The further loss of aluminium leads to a rearrangement of the remaining nickel atoms into the stable face-centred cubic structure of nickel. This transformation occurs by small adjustments of nickel atoms over short distances resulting in crystallites in the size range of a few nanometers.