Dissolution Velocity of Oxygen from H₂O-Ar Atmosphere into Molten Iron

On the kinetics of gas/molten iron reactions-I

Abstract

In order to study the kinetics of reaction between atmosphere and molten iron, we investigated the rate and mechanism of oxygen dissolution from H₂O-Ar atmospheres into molten iron. Results are as follows:
The mechanism of reaction is supposed to occur in three steps. At first, H₂O molecules from the atmosphere diffuse on the gas/molten iron interface, and the diffusion rate equation may be expected to be dm/dt=D_mFM (P_H2O-P_H2Oi) /δ_G (1). At the gas/molten iron interface, the chemical equilibrium, H₂O (g) =H₂ (g) +O, is always attained. At the last step, O diffuses from the surface of molten iron into the core, and the corresponding equation may be dm/dt =D_LF_ρ ([O] _i- [O]) /VδL (3). When Eq. (1) is larger than Eq. (3), O is accumulated on the surface of molten iron and an oxide layer forms.
On the basis of the kinetic theory of gas molecules, it was confirmed that the chemical reaction between H₂O and Fe hardly proceeded in a gaseous phase of the lack of Fe vapor, and it was supposed that the chemical reaction took place only at the gas/molten iron interface.
Experimental data seem to show that the rate determining step of the reaction is the diffusion of H₂O through the diffusion layer in the gaseous phase at the gas/molten iron interface in cases where no oxide laye-rs appear at the surface of molten iron. In these cases, the rate of reaction is approximately proportional to the partial pressure of H₂O in atmosphere. When an oxide layer appears on the surface of molten iron, the reaction becomes one of gas/slag/molten iron and the rate determining step is the transport of O from the surface of molten iron into the core.