On the Activity of Iron Oxide in the Silica-Saturated Slags

Abstract

The general relationship between oxygen in the liquid iron and iron oxide in the slag is well understood as the distribution of oxygen.
There are many reports dealing with the equilibrium between ternary slag FeO-CaO-SiO₂ and FeO-MnO-SiO₂ and oxygen in the liquid iron. And also, thermodynamical consideration on the variation in chemical properties of oxides in the slag has been made by many workers. It is, however considered that their theories involved in themselves some questions and assumptions. Authors measured the effects of the following oxides, namely, CaO, Al₂O₃, MnO, CrO, on the distribution of oxygen and examined the distribution coefficients of chromium for the quaternary system, FeO-CrO-CaO-SiO₂ saturated with silica and liquid Fe-Cr alloy.
Authors discussed on the questions whether or not the distribution of chromium in this system could be given as a linear function of iron oxide as shown by KORBER et al., or activity of iron oxide, the same as FeO-CrO-MnO-SiO₂ system reported previously by authors.
The equilibrium between the molten iron and the slag was studied in the silica crucible at 1600°C. The results obtained are summarized as follows.
1) The effects of various oxides on the silica content in the silica saturated slag correspond to the melting point of its silicate.
2) The solubility of oxygen decreases with an increase in the added oxide in FeO-SiO₂ system. It is recognized that there exists some relationship between the diminution rate of oxygen and the strength in terms of the basicity of added oxide.
3) The effects of various oxides on the activity of iron oxide are relatedwith the strength in terms of the basicity of added oxide. The activity of iron oxide was representedby the following empirical formula.
a_FeO=0.388-(1.30N_M²⁺-1.14N²_M²⁺)/√I
where I refers to the ion-oxygen attraction.
4) The equilibrium relation between three forms of oxygen in silicate melts as shown by RICHARDSON was studied for the ternary slags saturated with silica.
The concentration of (O^2-) was abruptly changed with the variation of cation in silica saturated slag.
5) Distribution of chromium was obtained for the quaternary slag FeO-CaO-CrO-SiO₂. The results show that the distribution coefficient of chromium is affected by CaO. And it can not be represented by the concentration of iron oxide as shown by KORBER et al., but by the activity of iron oxide. It showed good agreement with the results reported previously for the system FeO-CrO-MnO-SiO₂ by authors.
6) Expedient method of calculating the activity of iron oxide in the quaternary system can be obtained by using the activity of iron oxide in ternary system. The calculated values showed close agreement with the experimental results.