The manganese activity in the liquid Ni-Mn alloys has been measured by an isobaric method with an alumina capsule in which Fe-Mn alloys have been used as a reference system. Results obtained are as follows: (1) Activity of manganese shows remarkable negative deviations from Raoult’s law compared with the Co-Mn system in low manganese concentration range and has close values to those of the Co-Mn system in high manganese concentration range in the vicinity of
NMn=0.9. In the concentration range, for
NMn≤0.5 it increases with increasing temperature and vice versa in the range,
NMn≥0.6. (2) Activity coefficients are expressed by the following equations:
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oindent(3) Behaviours of thermodynamic properties, γ
Mn,
ΔH and
Δ\bar
SMnXS, for the liquid Ni-Mn system indicate that the Ni-Mn system can be regarded neither as an ideal solution such as the liquid Fe-Mn system nor as a regular solution such as the liquid Co-Mn system. (4) Activities for the liquid Ni-Mn system are well described quantitatively by an ideal associated solution model, assuming the formation of species of associated compounds, NiMn and Ni
3Mn, whose stoichiometric compositions are equal to those of the compounds in solid state. (5) Plots of lnγ
°Mn in X (X=Mn, Fe, Co, Ni) against
ZX show a convex curve with a maximum between
ZFe and
ZCo. A similar curve has been also found in the plots of the magnetic moment of the solid alloys against
ZX.
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