3050.     ---------------.  [SCHENCK, R.]  [Equilibrium Relations in the Reduction, Oxidation and Carburization of Iron.  I.]  Ztschr. anorg. Chem., vol. 164, 1927, pp. 145-185; Chem. Abs., vol. 21, 1927, p. 3334.

                    Thorough study of the systems represented by the following 2 reactions is undertaken:  (I) Ch₄=C+2H₂, (II) CH₄+3Fe=Fe₃C+2H₂.  CH₄ was prepared either by treating Al₄C₃ with water or by fractionating liquefied natural gas.  H₂ was prepared electrolytically and by the action of Al on alkali.  To facilitate reaction the Fe used was deposited on porous pieces of pumice.  The pumice was soaked in Fe(NO₃)₃ solution, heated to redness, and the Fe was obtained by reduction in H₂.  Pure Fe₃C was prepared by the action of CH₄ on Fe at 700°.  The reactions 300°-500° were carried out in a Jena glass tube heated to constant temperatures by contact with liquids at their boiling points.  Reactions 500°-900° were carried out in porcelain tubes heated in an electric tube furnace, the temperature being kept constant to within 2°.  The progress of reactions (I) and (II) at the various temperatures was follows by reading the pressure developed in the reaction tubes.  No CH₄ is decomposed by Fe at 300°. At 350°, about 1% by vol. is decomposed, and the presence of Fe₃C can be detected.  At 445°, about 4.4% is decomposed.  The proportions are the same if H₂ is passed over heated Fe₃C, thus proving the existence of a true equilibrium in reaction (II).  The decomposition of CH₄, according to reactions (I) and (II), is plotted against 2 branches.  One along which CH₄ and H₂ are in equilibrium with ferrite and dilute carbide-ferrite mixed crystals, the other along which the gases are in equilibrium with Fe₃C and concentrated carbide-ferrite mixed crystals.  The points of similarity between the systems studied and the Fe-C system are pointed out.  Using his experimental results, Schenck calculates that the heat of formation of Fe₃C is -15,405 cal. in close agreement with the values obtained calorimetrically.  This is taken as a proof that the observations made really pertain to the equilibrium represented by reaction (II).  Schenck outlines the application of the findings to problems arising in the carburization of Fe by hydrocarbons.  From the data obtained for systems (I) and (II) and the previously determined equilibrium relations in the system 2 CO=C+CO₂, are calculated and plotted the equilibrium relations, which, theoretically, should exist in the system 3 Fe+2 CO=Fe₃C+CO₂.