The structure of Raney nickel: II. Electron microprobe studies

Abstract

The activation of Raney nickel alloys containing 42 and 50 wt % Ni by reaction with aqueous sodium hydroxide was studied by metallographic methods including an electron probe microanalyzer. The alloys contained a eutectic of about 5 wt % Ni, β(NiAl 3), and γ(Ni 2Al 3) phases; NiAl was not found in these alloys. For any phase the attack by alkali advances as a front yielding a sharp gradient between alloy and activated catalyst, or, in the case of eutectic, a void. In activated catalysts portions originating from β and γ alloys can be recognized on the basis of structural characteristics. The activated materials contain what appears to be shrinkage cracks, which are larger and more numerous in catalyst derived from β- rather than γ-phase. In moderately concentrated aqueous alkali, the eutectic and β phase react more rapidly than γ phase. For example, in a 10-min leaching of 30–50 mesh alloy at 50 °C in which half of the aluminum was oxidized, the product contained activated β-phase and γ alloy. In dilute alkali the attack on the alloy was non-selective and the catalyst contained substantial amounts of alumina. Our data indicate that analyses of moderate accuracy can be obtained on the porous activated Raney nickel by the electron probe microanalyzer.