Deoxydation with Silicon and Manganese in the Liquid Iron-Chromium Alloy and Equilibrium between Silica Saturated Slag and Liquid Iron.

Abstract

The equilibrium between the liquid iron-chromium alloy and the slag containing FeO, MnO, CrO and saturated silica was studied in the SiO₂ crucible at 1550°C, 1600°C, and 1650°C
The equilibrium constants for the deoxydation of silicon in the molten iron containing manganese and chromium were calculated by using the thermodynamical equation introduced by C. WAGNER, and compared with the experimental values.
Even if the calculation was uncomplete in the dilute solution, the relations between the concentrations of various components could be evaluated by using the Wagner's equation, but these thermodynamical calculations of oxides in the slag, even if the oxides were limited to a few components, could be carried out only using the Gibbs-Duhem equation and it was impossible for the multi-component systems.
In the present paper, various metallic oxides in the silica saturated slags were considered about how they react with the various elements in the molten iron. The results are summarised as follows.
1) The equilibrium constant for the deoxydation of silicon was evaluated by using the various interaction parameters, and it turned out higher than that in the liquid iron-chromium alloy with an increasing chromium concentration.
In a multi-component system, it is assumed that the deviations of the equilibrium constants occur with the errors in the experimental procedure, errors in the interaction parameters and neglect of all terms after the second in the Wagner's equation.
2) The activity of iron oxide increased with an increasing chromic oxide and a decreasing manganese oxide.The reason for this is assumed to be that the free ferrous ion in the silicate slags was increased with the ionic reaction between chromium and iron.
The activity of iron oxide was independent of temperature, and depended on the concentrations of coexistent components.It exhibited negative deviation from the Raoult's law.
3) The distribution coefficients of chromium are affected by chromic oxide and manganese oxide and do not show good agreement with those of Körber and Oelsen.The relation between the distribution coefficients of chromium and the activity of iron oxide was represented approximately by the equation.
L_cr=54·εα_Feo+0·38
4) The distribution coefficients of manganese also do not show good agreement with those of Körber and Oelsen.The relation between the distribution coefficients of manganese and the activity of iron oxide was represented approximately by the equation.
L_MN (5·37×10⁷/T-2·63×10⁴)·aα_Feo
5) The effects of chromium and manganese on the solubility of silicon were measured and by arbitrarily choosing the two elements in the molten iron, the concentrations of the other two elements and the oxides in the silicate slags can be determined.