熔鐵中の共存元素の活量について(II)

熔鐵中の珪素の活量

抄録

Constructing the following electrode concentration cell, authors measured electromotive force corresponding to the change of silicon content in iron by a potentiometer.
The temperature range of the experiment was 1, 520-1, 530°C and for measurement of the temperature a Pt-Pt-Rh thermocouple was used. As preliminary experiments, the reversibility and thermoelectromotive force were investigated.
The theoretical relation between electromotive force E and the activity of silicon a_Si was as follows:
where a'_Si: the activity of pure silicon
aⁱ_Si: the activity of silicon ion in the molten slag.
Because pure silicon was selected as a standard state, then the following equation was obtained from eqn. (1)
n was approximately determined as n 4 by calculation from the authors' data.
The activity of silicon was obtained by substituting the values E, n and T to eqn. (2).
Being judged from this result, Fe-Si binary solution was recognized to be a semi-regular solution and obeyed to Henry's law up to about n_Si=0.10
Furthermore, the free energy change ΔG⁰_{1, 793} of the following reaction at 1, 520°C was calculated from the author's data.
ΔG⁰_{1, 793} represented the free energy of solution of silicon at unit activity on a scale in which the activity was equal to percentage at infinite dilution. To convert this to activity on a mole fraction scale in which the activity of pure liquid silicon was unity, the following eqn. (4) was required
From the relation between log(A_Si/n_Si=γ_Si) and square of the mole fraction of iron n²_Fe, activity coefflcient γ⁰_Si which represented γ_Si at n_Fe=0 was obtained as 0.013. and the mole fraction of silicon in dilute solutions was 0.0199 times its weight percentage. From these two values, the ratio of the activities of silicon on the two scales was obtained as 0.00026.
Substituting this value to eqn. (4), authors obtained the following value