Oxidation and crystallization behaviour of amorphous Ni64Zr36 alloy

Abstract

The oxidation and crystallization of an amorphous Ni₆₄Zr₃₆ alloy has been investigated in the temperature range 690–750 K using thermoanalytical methods and X-ray diffraction. The dominant reaction was the oxidation of Zr to ZrO₂. Even at complete conversion of the zirconium, only little NiO was detected in the oxidized alloy. The oxidation led to crystallization and phase separation of the amorphous alloy. The oxidized samples contained well dispersed metallic nickel particles which were embedded in an oxidic matrix consisting of mainly tetragonal and a little monoclinic ZrO₂. The degree of oxidation of the solid samples did not influence the crystallization behaviour of the unreacted alloy. The heat of crystallization referred to the non-oxidized part of the alloy was ca. 40 J g^–1 and independent of the degree of oxidation. The experimental kinetic data of the oxidation were fitted with a model based on the assumption that diffusion of the reactant oxygen through the oxide layer to the unreacted core of the alloy particle is the rate-controlling step. The model is applied to predict conversion–time profiles in the temperature range 570–750 K.