3056.     SCHENCK, R., AND KLAS, H.  [Equilibrium Relations in the Reduction, Oxidation and Carburization of Iron.  VII.  (8).  Cobalt in a Methane-Hydrogen Atmosphere.]  Ztschr. anorg. Chem., vol. 178, 1929, pp. 146-156; Chem. Abs., vol. 23, 1929, p. 2116.

        Two reactions are possible, 1 in which Co acts purely as a contact substance, expressed by the equation CH₄=C+2 H₂, and 1 in which the formation of carbide occurs; nCo+CH₄=Co_nC+2 H₂.  The system is investigated in the range 680°-900°, and the composition of the gas phase is varied between 0 and 100% for both H₂ and CH₄, with small additions of CO and N₂.  The presence of Co-Co carbide mixed crystals follows from the gradual increase in % CH₄.  At first more diluted mixed crystals are formed, which are in equilibrium with low CH₄ concentrations.  With carbide increase in the solid solution, CH₄ concentration increases, reaching its maximum when saturation with carbide is attained, and the occurrence of the pure carbide phase begins.  This saturation concentration of CH₄ is about 18% at 680°, 15% at 700°, 14% at 720°, 10% at 760°, 7.5% at 800°, and 3.7% at 900°.  Co carbide is found to be more stable than Fe carbide.  Complete decarburization is not obtained with less than 97% H₂ in the gas phase.  Phase diagrams are given that show the limits of the mixed crystal field.