3053.     ---------------.   [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.  IV.  (5).  Iron Carbide, Iron Oxides, and Iron Under an Atmosphere of Carbon Monoxide and Carbon Dioxide.]  Ztschr. anorg. Chem., vol. 167, 1927, p. 254-314; Chem. Abs., vol. 22, 1928 p. 937.

        FeO is prepared by heating FeC₂O₄ in vacuo.  It is mixed with powdered Fe and finely divided C, and the mixture is subjected to a CO₂ atmosphere at definite temperatures.  The concentrations of CO and CO₂ are determined after equilibrium has been established.  Wüstite and oxoferrite are formed as has been reported.  The addition of small quantities of Hg tot he system reduced the solubility of FeO in Fe and, thus, produced an oxoferrite (solid solution of FeO in Fe) of relatively low O₂ content. Likewise the wüstite formed was poorer in O₂ and, hence, was nearer FeO in composition.  the CO-CO₂ atmosphere above the mixture also was poorer in the O₂-rich CO₂l than was the case when Hg was absent from the mixture.  This is another illustration of the marked influence that foreign substances have upon the equilibrium in the Fe-C-O₂ system.  Quantitative studies of the influence of additions of other substances are in progress.  Pure Fe was partly changed to Fe₃C by cementation, CH₄ being used.  This carburized mixture then was allows to come to equilibrium at various temperatures under an atmosphere of CO and CO₂.  Both C and O₂ are absorbed by the solid phases.  The results indicate a bivariant equilibrium with the following 3 phases:  (1) Gaseous (CO and CO₂); (2) Fe₃C; (3) ternary solid solution of Fe₃C, FeO, and Fe.  For the ternary solid solution the name “oxoaustenite” is suggested.  This solution also is undoubtedly present in the univariant equilibrium mixtures of wüstite, oxoferrite, CO, and CO₂, since the solid phases always yield either free C or hydrocarbons upon treatment with diluted acids.  The reaction between Fe₃C and Fe₂O₃ and Fe₃O₄ was studied by heating known mixtures to 600°, 650°, and 700°.  When equilibrium has been attained, the pressure and composition of the evolved gases are determined.  The following concurrent reactions occur:  (1) 4 Fe₃C+Fe₃O₄=15 Fe+4 CO, (2) 2 Fe₃C+Fe₃O₄=9 Fe+2 CO₂.  An isotherm at 650° shows the equilibrium existing at definite total pressures and definite concentrations of CO.  The phases appearing are Fe₃O₄, wüstite, Fe₃C, oxoaustenite, and gas.  The equilibrium diagram is given for the system wüstite-oxoferrite-oxoaustenite from 600°-1,000° at 1 atm. pressure and under varying concentrations of CO.