Abstract
The thermodynamic activities of iron in iron-nickel alloys have been determined by e.m.f. measurements on solid-electrolyte oxygen concentration cells over the temperature range 750–1150°C.
Pt/Fe, FeO//ZrO2·CaO//Fe–Ni alloy, FeO/Pt.
The activity of iron in the Fe–Ni system exhibits slightly positive departures from ideal solution behavior in the iron-rich alloys and negative departures in the nickel-rich alloys. The activities of nickel, deduced from the Gibbs-Duhem equation, indicate negative departures from ideality in the entire composition range.
The relative integral molar excess entropies are positive for all the compositions studied. However, a consideration of the magnetic factors suggests that the configurational excess entropies are negative and that the solid solutions are non-random.
The heats of mixing vary from the endothermic to exothermic values with increasing nickel content. It is inferred that the non-random behavior suggested by the presumed configurational excess entropies is clustering at the iron-rich compositions and short-range ordering at the nickel-rich compositions.
