Redox Equilibria in Wustite Doped with CaO, SrO and BaO

Abstract

This study was performed to obtain the concentration of defects and the activities of components in wustite doped with MeO(Me: Ca, Sr and Ba). The composition as FeO-Fe_2⁄3O-MeO for wustite in equilibrium with CO-CO₂ gas mixtures of P_CO2⁄P_CO=30⁄70, 50⁄50 and 60⁄40 at each temperature of 1273, 1373 and 1473 K, was determined by an analysing method utilizing the weight loss during reduction. The concentration of cation vacancy (V_Fe^\varparallel) is estimated as one-third of the mole fraction of Fe_2⁄3O. The value of (V_Fe^\varparallel) increases with an increase in the amount of MeO and in the ionic radius of Me except for the higher concentrations of CaO. The increase in the value of (V_Fe^\varparallel) may be interpreted qualitatively by considering that the strain generated due to the difference in radius in the substitutional dissolution of MeO can be relieved by the formation of an association [Me_Fe^×·V_Fe^\varparallel]. Furthermore, the activities of FeO and MeO were estimated by Schumann’s method from the oxygen pressure contours for wustite doped with CaO at 1273 K.