Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb

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

“…Furthermore, the niobium oxides in the slags were proved to be NbO 2 in the previous study under the same experimental condition. [18] As shown in Tables I and II, no large composition variations of the slags were observed before and after the equilibrium process between the slags and Fe-Nb/ Cu-Nb melts, respectively. Besides, the difference in the compositions of the slags of the Fe-Nb and Cu-Nb melt in the 1-1 group was very small after the experiment, which can be ignored.…”

“…Henrian Activity Coefficient of Nb in Fe-Nb Melts There has been a study to determine the Henrian activity coefficient of Nb in copper liquid by equilibrating the pure solid NbO 2 with liquid copper. [18] However, the CaO-MgO-Al 2 O 3 -NbO 2 slags, instead of pure solid NbO 2 , were used to determine the Henrian activity coefficient of Nb in Fe-Nb melts in this study. The main reason for the using of CaO-MgO-Al 2 O 3 -NbO 2 slag instead of pure NbO 2 slag is that, when the pure NbO 2 slag was used, iron-niobium composite oxides may be formed, which will affect the composition of the slag.…”

“…To achieve this goal, the study of the Henrian activity coefficient of Nb in Nb-Cu melts, c o ½NbðCuÞ , was utilized, in which the c o ½NbðCuÞ was measured by equilibrating solid NbO 2 with liquid copper under a controlled oxygen potential at 1873 K (1600°C). [18] The equilibrium reaction of NbO 2 in the slags with Cu-Nb melts can be written as follows:…”

“…According to this, slags with exactly the same composition were used to equilibrate with liquid iron and liquid copper, respectively, under exactly the same oxygen potential at 1873 K (1600°C) in this study. Based on the fact that the Henrian activity coefficient of Nb in the Cu-Nb melts, c o ½NbðCuÞ , was determined to be 309.74 at the same condition, [18] the Henrian activity coefficient of Nb in Fe-Nb melts, c o ½NbðFeÞ , can be obtained by determining the mole fractions of Nb in Fe-Nb melts and Cu-Nb melts.…”

“…Thus, the value of the activity interaction parameter of V to Nb, e V Nb , can be deter-mined by obtaining the slope of the linear relation between the left side of Eq. [18] and w½V % . Equation [18] is shown as follows:…”