Activity coefficients of Al and Fe in Al-Fe alloys were measured in the temperature range from 1400 to 1600°C by the use of knudsen cell mass spectrometer.
Activity curves through the whole composition range were shown for 1400°C.
At higher temperatures, measurements with alloys of high aluminum concentrations and at lower temperatures, measurements with alloys of low aluminum concentrations could not be performed because of experimental difficulties.
It was confirmed that the activity coefficient of Al followed Darken's quadratic formalism in the temperature and composition ranges investigated.
From the temperatuer dependence of the value lim ln (I
+AlN
Fe/I
+FeN
Al), the temperature dependence of lnγ°
Al was determined. By combining the equations of tomperature dependences of lnγ°
Al and α
FeAl, the following equations were derived for the activity coefficient of Al in Al-Fe alloys. for solid alloys with N
Al≤0.33 for liquid alloy with N
Al≤0.17.
The temperature dependence of the interaction parameter ε
(Al) Al can be given by for solid alloy and for liquid alloy.
From these equations values for γ°
Al and ε
(Al) Al at 1600°C are calculated as follows:
Temperature dependences of γ°
Fe and ε
(Fe) Fe are also derived as:
and ε
(Fe) Fe=2280/T+6.93
From these equations, values for γ°
Fe and ε
(Fe) Fe at 1600°C are calculated as follows:
From the temperature dependence of lnγ°
Al, the limiting molar heat of mixing of Al in Al-Fealloy at the infinite dilution of Al was calculated to be -17000 cal.
The obtained values were compared with the results of the previous investigatons.
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