Knudsen Cell-Mass Spectrometric Study of the Thermodynamic of the Iron-Aluminum Alloys

Abstract

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.