3057.     SCHENCK, R., DINGMANN, T., KIRSCHT, P. H., AND WESSELKOCK, H.  [Equilibrium Studies of the Reduction, Oxidation, and Carburization Process of Iron.  VIII.  (9).  System Iron-Oxygen.]  Ztschr. anorg. Chem., vol. 182, 1929, pp. 97-117; Chem. Abs., vol. 24, 1930, p. 44.

        Object was to study the minima attained in the oxidation of Fe with small quantities of CO₂ and their dependence upon the O₂ content of the basic material.  The O₂ saturation of the homogeneous oxyferrite phase at different temperatures likewise was determined.  The metal used in the experiments was carefully freed of H₂ by many days heating in a high vacuum, while the gas used was pure CO₂ gas under diminished pressure or, in a few cases, mixtures of CO₂ and CO.  At 700°, the reaction velocity was very slow, while at 1,000° the stable zone was reached in the course of the 1^st day.  The stable wüstite-oxyferrite equilibrium corresponds at 700° to a gasp phase composition of 40.3% CO₂ and 59.7% CO, at 800° to 35.1% CO₂ and 63.9% CO, and at 1,000° to 28.5% CO₂ and 71.5% CO.  At 800° and 1,000° the O₂ taken up in homogeneous solid solution is about 0.4%, the higher values previously obtained being due to the occurrence of a metastable wüstite poor in Fe₃O₄.  With mixtures of CO₂-CO, the relation between CO and CO₂ in the gas phase was determined along the stable wüstite-oxyferrite boundary.  The new values for maximum O₂ content require a diminution in the extent of the oxyferrite zone in the Fe-O equilibrium diagram.  The possibility of preparing FeO in the pure state is discussed, and it is suggested that small additions of MgO or MnO would increase the stability of FeO.  Addition of 0.5%, 1.0%, and 4.0% Cu as well as 4% Ni was studied and resulted in a slight displacement of the wüstite-oxyferrite border toward higher CO₂ concentration, as well as a more rapid attainment of the stable wüstite-metal boundary.  The solubility of O₂ is reduced more than 50%.