Study on Reaction Diffusion in the Nickel-Zinc System

Abstract

Pure nickel-pure zinc diffusion couples were annealed in the temperature range from 483 to 873 K. Diffusion layers were formed step by step as in the case of the iron-zinc system. Above 613 K five layers, δ, γ′, γ'″, γ″ and γ₁, were detected, although γ′, γ'″ and γ″ layers were not presumed to be formed from a point of view of the equilibrium phase diagram.
Anantatmula et al. measured the thermodynamic activity in the nickel-zinc system and found that the value of lnγ_Zn changed abnormally at about 17 at%Ni in the homogeneous region of the γ phase. They concluded that the abnormal change of the activity would be caused by an interaction between the Fermi surface and the Brillouin zone in the γ phase of γ brass structure. The concentration gap at the boundary of γ′⁄γ'″ layers ranged from 16 to 18 at%Ni and within this composition the activity showed an abnormal behaviour. There are two possible interpretations of the formation of the γ′ and γ'″ layers; one is that the interdiffusion coefficient reaches a minimum at 17 at%Ni, and the other is that there is a miscibility gap around the same composition mentioned above.