Determination of Thermodynamic Properties of Nb in Fe-Nb, Fe-Mn-Nb and Fe-Mn-Nb-V Melts at 1873 K

The Henrian activity coefficient of Nb and the interaction parameters of Mn and V to Nb in liquid iron at 1873 K (1600 °C) were accurately determined by using the chemical equilibrium technique. CaO-MgO-Al₂O₃-NbO₂ slags with different compositions were equilibrated with liquid iron and Fe-Mn melts, respectively, to determine the Henrian activity coefficient of Nb in liquid iron, \( \gamma_{\text{Nb(Fe)}}^{\text{o}} \), and the interaction parameters of Mn to Nb in liquid iron, \( e_{\text{Nb}}^{\text{Mn}} \), \( r_{\text{Nb}}^{\text{Mn}} \), \( r_{\text{Nb}}^{\text{Nb}} \) and \( r_{\text{Nb}}^{\text{Mn,Nb}} \). The CaO-MgO-Al₂O₃-NbO₂-V₂O₃ slag with a fixed composition was equilibrated with Fe-Mn melts to determine the interaction parameter of V to Nb in liquid iron, \( e_{\text{Nb}}^{\text{V}} \). The samples were placed in alumina crucibles and equilibrated at 1873 K (1600 °C) for 24 hours. An Ar-CO-CO₂ gas mixture was employed to control the oxygen potential of the system. The \( \gamma_{\text{Nb(Fe)}}^{\text{o}} \) was determined to be 0.145. The first-order interaction parameters \( e_{\text{Nb}}^{\text{Mn}} \) and \( e_{\text{Nb}}^{\text{V}} \) were determined to be − 2.025 and − 3.07, respectively. The second-order interaction parameters \( r_{\text{Nb}}^{\text{Nb}} \), \( r_{\text{Nb}}^{\text{Mn}} \) and \( r_{\text{Nb}}^{\text{Mn,Nb}} \) were determined to be 0.196, 0.166 and − 0.377, respectively.