Deoxidation Equilibrium of Aluminum and Silicon in the Liquid Iron-Nickel Alloys

Abstract

Thermodynamic analysis and experiments showed the deoxidation ability of aluminum in the iron-nickel melts to be lower than that in pure iron and nickel. With an increase in the nickel content, the deoxidation ability of aluminum decreases to about 50% Ni and then it rises. In pure nickel, the deoxidation ability of aluminum is almost equal to that in pure iron. On one hand, this can be explained by an increase in the bond strength of aluminum with this melt when the nickel content rises (γ°Al(Fe)=0.049, γ°Al(Ni)=0.00022) and, on the other hand, by a decrease in that of oxygen (γ°O(Fe)=0.0105, γ°O(Ni)=0.357). Curves of the oxygen solubility pass through the minimum whose location is independent of the nickel content in melt. The minimum oxygen concentrations are reached at ∼0.2% Al; the further additions of aluminum result in a rise in the oxygen concentration. Experimental and calculated results are in good agreement.Complex deoxidation of Fe-40%Ni with aluminum and silicon has been experimentally studied. The formation of solutions and chemical compounds between oxides of these elements promotes the participation of silicon in the deoxidation. The lower oxygen concentrations are reached after the combined deoxidation in comparison with the aluminum deoxidation. However, when the aluminum content rises in the melt at the same silicon concentration, this difference decreases; at a certain aluminum concentration, its deoxidation power becomes equal to that of complex action of aluminum and silicon. This occurs due to an increase in the content of aluminum oxide in slag. When the slag is saturated with aluminum oxide (aAl2O3=1), silicon does not take part in the deoxidation.