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  The gaseous phase consisting of CO and CO2 then was withdrawn and analyzed.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.