EFFECT OF FOREIGN CATION OF ZN(II) OR MN(II) ION IN FEO-WUSTITE ON ITS DISPROPORTIONATION REACTION BELOW 575-DEGREES-C

The transformation of the Zn(II)- and Mn(II)-wustites into wustites co ntaining Zn(II) or Mn(II) ions, and the spinel-type compound was studi ed to investigate the effect of foreign cations [Zn(LI), Mn(II) ions] in the FeO-wustite on the disproportionation of the FeO-wustite into a lpha-Fe and Fe3O4 below 575 degrees C. In these transformation reactio ns, the Fe(III) ions in the Zn(II)- and Mn(II)-wustites (Znx2+Fey2+Fez 3+O, Mnx2+Fey2+Fez3+O; x+y+z<1) form a spinel-type structure in Ar gas at 500 degrees C [Zn(II)-wustite] and 450 degrees C [Mn(II)-wustite], but no alpha-Fe phase appeared, indicating that the presence of those foreign cations in the FeO-wustite interferes with the disproportiona tion into alpha-Fe and Fe3O4 bellow 575 degrees C. During the transfor mation reactions of the Zn(II)-wustite, most of the Zn(II) ions in the wustite form ZnO and a small amount of the Zn(II) ion is left in the wustite. The stabilization energy for the formation of magnetite from Zn(II)-wustite with a lower Zn(II) content may be small and can not co mpensate for the increase in Gibbs energy due to alpha-iron formation from Zn(II)-wustite.