X-ray diffraction study of the transition kinetics of α- to β-nickel monosulfide

Abstract

This kinetics of the transition α-NiS/α-Ni1-xS → β-NiS/β-Ni1-yS has been investigated using a series of anneal-quench experiments. X-ray diffraction was used for phase identification and quantitative analysis. Initial bulk compositions of α-NiS/α-Ni1-xS play important role in the kinetics of the transition. The activation energy for this α- to β-phase transition is 20.01 kJ.mol-1 for the stoichiometric composition NiS. For nickel deficient composition α-Ni1-xS, however, Ea varies from 17.0 to 70.0 kJ.mol-1 depending on the extent of transition. The relationship between Ea and extent of transition for the initial bulk Ni0.97S was derived using the Refined Avrami method. The effect of initial composition of α-Ni1-xS also reflects on the reaction rate. The composition of exsolved β-Ni1-yS in a α-Ni1-xS matrix is more close to stoichiometric composition NiS than is α-Ni1-xS. A distinct induction period of the α- to β-phase transition was observed due to the slow formation rate of the more nickel rich β-phase embryos.