The structural transitions during leaching of Ni2Al3 phase in a Raney Ni-Al alloy

The microstructure transitions during leaching of a rapidly solidified Ni-A l alloy have been investigated by means of X-ray diffraction, transmission electron microscopic (TEM) and high resolution electron microscopic (HREM) techniques. Ni2Al3 was the main phase in the starting Ni-Al alloy. The micr ostructure of the Raney nickel catalyst consists of nano-scale nickel cryst allites, residue of source phases surrounded by nano-scale boundary regions . The transformation during leaching of Ni2Al3 phase was an advancing inter face type process. Clusters of AuCu-structure type face-centrered tetragona l Ni3Al2 as an intermediate phase seems to appear in the reaction front. Ba sed on an analysis of the atomic configurations of phases Ni2Al3, Ni3Al2 an d nickel, a reasonable explanation for the transition mechanism during leac hing of Ni2Al3 phase and the arc characteristic of diffraction spots was pr oposed. The nickel crystallites generated during leaching obey an orientati on relationship with the source Ni2Al3 phase, which is consistent with the Delannay's orientation relationship proposed for nickel and NiAl phases. Th e nano-scale structural characteristic of the Raney nickel catalyst, especi ally its porous structure at the boundary regions, provides an excellent hy drogenation catalytic activity and selectivity of the catalyst. (C) 2001 Kl uwer Academic Publishers.