Thermodynamic activities in iron-nickel alloys

Abstract

The activity of Fe in iron-nickel alloys was studied in a differential apparatus by equilibrating mixtures of H 2O H 2 gases over pure iron and over the alloys. Errors due to thermal diffusion are minimized in this design, and the measured activity of iron is corrected for the variation of the activity of wüstite with ambient gas composition. Formation of magnetite prevents the investigation of nickel-rich alloys. In the iron-rich face-centered cubic alloys the solid solution is very nearly ideal; the activity coefficients are generally only slightly smaller than unity, the entropies of mixing are slightly larger than the ideal values, and the heats of mixing are small positive numbers.