Evolution of Microstructure and Catalytic Activity in Melt-Spun and Aged Ni3Al Ribbons

The Ni3Al intermetallic compound with nominal composition close to Ni75Al25 was produced by melt spinning technique. The obtained ribbon flakes were 50-100 µm in thickness and about 7 mm in width. The microstructures of as-cast and heat-treated ribbons were investigated by x-ray diffraction, scanning and transmission electron microscopy. The as-cast ribbons were not uniform in composition: The microstructure comprised the Ni3Al partially ordered phase and the Al-rich NiAl phase with the L10 martensite structure. Secondary annealing performed at 1220 K homogenized the microstructure and improved atomic ordering, and the latter increased considerably in comparison with the as-cast state. The catalytic properties of the as-cast and heat-treated ribbons, in powdered form, were tested for hydrogenation of phenylacetylene. It was shown that the use of annealed ribbons resulted in improvement in catalyst’s activity compared to the as-cast state: The degree of conversion increased up to 35%, whereas the reaction products ratio increased up to 86%.