3052.     SCHENCK, R., DINGMANN, T., BÖKMANN, J., EBERT, W., KESTING, W., LEPETIT, G., MÜLLER, J., AND PRATJE, W.  [Equilibrium Relations in the Reduction, Oxidation and Carburization of Iron.  III.  (4).  Systematic Investigations of the Oxidation-Reduction Relations Existing in the Systems of the Iron Oxides with Iron, Carbon Monoxide, and Carbon Dioxide.]  Ztschr. anorg. Chem., vol. 166, 1927, pp. 113-154; Chem. Abs., vol. 22, 1928, p. 566.

        Continuation of the work that will finally lead to knowledge of the equilibrium relations in the system Fe-C-O₂.  A precision method is used to determine the equilibrium relations in the systems Fe₃O₄+CO=3 FeO+CO₂ and FeO+CO=Fe+CO₂, the vapor phase in each case being a mixture of CO and CO₂.  Simultaneously the regions of stability of solid solutions of FeO and Fe₃O₄ and of FeO and Fe were established.  The method used allowed the oxides of Fe to interact at a definite temperature with a small quantity of CO until equilibrium was established.  The gaseous phase consisting of CO and CO₂ then was withdrawn and analyzed.  These small additions of CO were continued until the oxides were deoxidized almost completely.  The material composing the boat containing the oxides had a pronounced influence upon the equilibria resulting.  The presence of MgO or SiO₂ produced noticeable changes in the equilibrium curves.  Similar changes in the curves would result from the addition of any foreign substances likely to form solid solutions with the Fe oxides or to combine with them.  Al₂O₃ produces little effect.  By plotting the % of CO or CO₂ in the gas phase against the temperature, the equilibrium diagram is obtained.  It discloses an invariant point 560°, at which Fe, FeO, Fe₃O₄, CO, and CO₂ can coexist.  The existence of 2 solid solutions is shown:  (1) A solution of small quantities Fe₃O₄ in FeO for which the same “wüstite” is coined, and (2) a solution of small quantities of FeO in pure Fe for which the name “oxoferrite” is coined.  Wüstite exists only above the nonvariant point, 560°, and 76% Fe, 24% O₂.  Below this it separates in Fe₃O₄ and oxoferrite.  FeO was not encountered as an independent solid phase, and it is, concluded, therefore, that this oxide cannot be made in a stable condition at temperatures up to 1,100°.  Below 560° Fe₃O₄ can be deoxidized to oxoferrite directly.  Adding MgO to the system lowers the invariant point markedly and broadens out the area of existence of wüstite.  The authors intend to study in detail the influence of CaO, Al₂O₃, MnO, and SiO₂.  The practical value of these researches is discussed.