Deoxidation Equilibrium of Niobium in the Iron-Nickel Melts

The oxygen solubility in iron-nickel alloys with niobium was experimentally studied in Fe-40 pct Ni melt at 1823 K (1550 °C). It was shown that the presence of niobium decreases the oxygen solubility in this melt. The equilibrium constant of interaction of niobium with oxygen dissolved in the Fe-40 pct Ni (\( \log K_{{(1)({\text{Fe - }}40\% {\text{Ni}})}} = {-}4.619 \)), the Gibbs energy of this reaction (\( \Delta {\text{G}}_{{(1)({\text{Fe - }}40\% {\text{Ni}})}}^{ \circ } = 161 ,210\,{\text{J}}/{\text{mol}} \)), and the interaction coefficients characterizing these solutions (\( e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{O}} = {-}0.630 \); \( e_{{{\text{O}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = {-}0.105 \); \( e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = 0.010 \)) were determined. In the wide concentration range, the equilibrium constants and Gibbs energy of interaction of niobium and oxygen dissolved in the Fe-Ni melts and the interaction coefficients for these solutions were calculated for 1823 K (1550 °C). For this temperature, the oxygen solubility in the niobium-containing Fe-Ni melts was also determined. With an increase in the nickel concentration in the alloy the niobium affinity to oxygen rises appreciably. This appears to be associated with a decrease in the bond strength between metal and oxygen in the melt as the nickel concentration increases (\( \gamma_{\text{O(Fe)}}^{ \circ } = 0.0084;\;\gamma_{{{\text{O}}({\text{Ni}})}}^{ \circ } = 0.297 \)).