It has been considered that the content of oxygen in the molten iron is reduced by addition of Si according to the following relation:
[O]2 · [Si]=const.
This relation has been deduced from the chemical equation 2[FeO]+[Si] ←→
2[Fe]+SiO2 under an assumption that the molten state of Fe-Si alloy
dissolves oxygen and hydrogen as an ideal solution. However, the mutual interaction
of Si atom with oxygen atom is stronger than that of Fe with oxygen, and so
oxygen atoms may have a tendency to localize itself around Si atoms and the
distribution of oxygen atoms in the molten iron may deviate from the random
distribution. In this case a considerable deviation from the relation [O]2 · [Si]=const. is expected.
We can compute the relations between [O] and [Si] by using the free energy formula of molten state of alloy which has been deduced from consideration of the influence of such a mutual interaction of the atomic arrangement in the previous paper, and we have
where B(T) is a constant depending only upon temperature, and Kβ
is a parameter indicating the difference of mutual interactions between Si-O
and Fe-O pairs, being considered as Kβ>1. If the concentration
of [O] is plotted against that of [Si] by the above equation with Kβ
as a parameter, it is shown that the content of [O] decreases as the concentration
of [Si] increases in a region of small [Si] and it attains a minimum value at
a certain concentration of [Si], over which it rather increases. The minimum
concentration of [O] increases with the increase of Kβ.
Direct verification of these results has not yet been performed, but an oxygen analysis in ferrosilicon alloys by Zaffe and Sims and experiments on the deoxidation by Ti in molten cast iron by Wentrup and Hieber can be explained only by our theory.
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