Thermodynamics of zirconium deoxidation equilibrium in liquid iron by EMF measurements

Abstract

Thermodynamics of Zr deoxidation equilibrium in liquid iron has been studied at 1 873 K by using ZrO2-9mol%MgO and mullite (3Al 2O3·2SiO2) 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±10kJ. The interaction coefficients for eOZr, rOZr and rOZr,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]) : eOZr=-3.70-2020 ln X-20.7(ln X)2+(ln X) 3 rOZr=dV/dX={-0.33+1.87 ln X+3.01 (ln X) 2}/X rOZr,O≈11.4rOZr={-3.72+21.4 lnX+34.3(ln X)2}/X © 2008 ISIJ.