Thermodynamics of Zirconium Deoxidation Equilibrium in Liquid Iron by EMF Measurements

Abstract

Thermodynamics of Zr deoxidation equilibrium in liquid iron has been studied at 1873 K by using ZrO₂–9mol%MgO and mullite (3Al₂O₃·2SiO₂) electrolytes coupled with the quantitative alalysis of soluble Zr and insoluble Zr as ZrO₂ by using a potentiostatic electronic extraction method. The soluble O content for a given soluble Zr content is lower than the previously reported values in the plot of soluble O vs. soluble Zr contents, and the oxygen activity for a given soluble Zr content is higher than the previously reported values. The free energy change of solid Zr dissolution into iron melt: Zr(s)=Zr at 1873 K is obtained as ΔG°=−153±10 kJ. The interaction coefficients for e_O^Zr, r_O^Zr and r_O^Zr,O are estimated as −70±15, 901±131 and 10300±1500, respectively. However, the following interaction coefficients are represented by using a continuous function of logarithms of X, where X=[%sol.Zr]+5.7[%sol.O]+17.1[%sol.Zr]·[%sol.O]/(2[%sol.Zr]+5.7[%sol.O]):
e_O^Zr=−3.70−2.20 ln X−2.07(ln X)²+(ln X)³
r_O^Zr=dY/dX={−0.33+1.87 ln X+3.01(ln X)²}/X
r_O^Zr,O<11.4r_O^Zr={−3.72+21.4 ln X+34.3(ln X)²}/X