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 n ickel-aluminium alloys in alkali solution. The structure of this leached re sidue was investigated using transmission electron microscopy and X-ray dif fraction. The leaching process selectively dissolves aluminium from the all oy and the remaining atoms form a nonequilibrium body-centred cubic phase o f disordered nickel and aluminium atoms. This phase exists over a wide rang e of compositions. The further loss of aluminium leads to a rearrangement o f the remaining nickel atoms into the stable face-centred cubic structure o f nickel. This transformation occurs by small adjustments of nickel atoms o ver short distances resulting in crystallites in the size range of a few na nometers.