Phase formation in the nickel—Zinc reaction couple

Annealing of Ni’MZn reaction couples at 400°C for 1–25 h results in the formation of intermetallic layers of the γ- and δ-phases at the interface between nickel and zinc. The width of the homogeneity region for the γ-phase is 73.0–86.0 at. % Zn, while that for the δ-phase is 87.5–89.0 at. % Zn. The chemical formula for the γ-phase is thus NiZn3–6, while that for the δ-phase is NiZn7–8. The γ-phase growth kinetics is described by a parabolic equation xi2’Mx02=2k1ti (xi and x0 are the thicknesses of the layer at times ti and t0=0, k1 is the growth rate constant): k1=(4.4±0.2)·10’M14 m2/sec. The δ-phase shows a deviation from the parabolic law since its growth rate constant decreases from 9.6·10’M14 m2/sec at t=1 h to 6.9·10’M14 m2/sec at t=25 h. The thickness ratio for the layers in this time interval chages by about 13%.