The ion intensities of iron in Fe-Mo alloys have been measured at 1 823K over the whole range of composition by the Knudsen cell-mass spectrometric method, and the activities of iron and molybdenum in this binary system were determined. In this method silver or iron was used as the internal standard substance to cancelthe constants which are intrinsic in the measurement and can not be determined. The activity coefficients of molybdenum and iron in the infinitely dilute solutions are as follows:
γ^o_Mo(1)=1.54(+0.32-0.26), γ^o_Mo(s)=0.70(+0.39-0.37) and γ^o_Fe(1)=6.0(±1.1)
The first and second order interaction parameters of molybdenum in liquid iron, ε^(Mo)_Mo and ε^(Mo)2_Mo in atomic fraction unit and e^(Mo)_Mo and e^(Mo)2_Mo in weight percent unit are represented as follows:
ε^(Mo)_Mo=4.1(±1.4), ε^(Mo)2_Mo=-11.0(±4.1) and
e^(Mo)_Mo=1.21×10^-2(±0.35×10^-2), e^(Mo)2_Mo=-1.1×10^-4(±0.8×10^-4).
Furthermore, the heat of sublimation at 298K and fusion of pure iron have been determined by the second law method as follows:
ΔH^s(α)₂₉₈=414kJ/g-atm
ΔH^m₁₈₀₉=15.1kJ/g-atm.