Abstract
The vapor pressures over manganese zinc ferrites with two kinds of oxygen contents (Mn0.676Zn0.261Fe2.063O4.031 and Mn0.676Zn0.261Fe2.063O4.000) were measured by mass-spectrometric method in the temperature ranges of 1,270~1,417 K and 1,258~1,398 K, respectively. As the main gas species over Mn0.676Zn0.261Fe2.063O4.031, three gas species of Zn(g), FeO(g), and MnO(g) were identified in order of decreasing partial vapor pressure. On the other hand, two gas species of Zn(g) and MnO(g) were only identified over Mn0.676Zn0.261Fe2.063O4.000. From the partial vapor pressures of Zn(g), FeO(g), and MnO(g) experimentally obtained in this study and the partial oxygen pressures for the specimen estimated according to the relation between composition and partial oxygen pressure previously reported, the partial vapor pressures of ZnO(g), Fe(g), and Mn(g), which were not detected experimentally, were calculated on the basis of the gas equilibria: MO(g)=M(g)+1/2O2(g), where M=Zn, Fe, and Mn. The manganese zinc ferrites with the compositions of Mn0.676Zn0.261Fe2.063O4+x(x=0.031 and 0.000) were concluded to be the incongruently vaporizing compositions, of which preferentially vaporizing species is Zn(g). The dependence of the vapor pressures on oxygen nonstoichiometry was determined. The enthalpies of vaporization of ZnO(g), MnO(g), and FeO(g) over ferrites were compared with those over ZnO(s), MnO(s), and Fe2O3(s), respectively.
