2705.     ---------------.  [PINGAULT, P.]  [Equilibrium Between Iron-Iron Carbide-Oxygen.]  Compt. rend., vol. 192, 1931, pp. 45-47; Chem. Abs., vol. 25, 1931, p. 1727.

        Fe-C-O diagram is completed by determining the curve representing the equilibrium between Fe and Fe₃C in mixtures of CO and CO₂.  In the apparatus used the gas was passed continuously through a closed circuit.  The 50-cc. samples were analyzed chemically with an accuracy of more than 0.5%.  The Fe was used in the form of fine wire, which made it possible with a small weight of material to fill the whole tube and obtained a rather large reaction surface.  The experiments were carried out at atmospheric pressure.  To insure having no false equilibrium due to passive resistance, Fe was carburized in a mixture rich in CO and decarburized in a mixture rich in CO₂.  Analysis showed that the 2 methods gave the same results at the same temperature.  When a mixture of FE and C was kept in a limited quantity of O₂ the results varied with the temperature:  Above 740° Fe₃C was formed, and CO₂ in the gaseous phase varied from 0-28%; between 740° and 700°, the proportion of CO₂ was 28-42%, and Fe₃C was oxidized to Fe and CO; below 700° the content of CO₂ became high enough to oxidize Fe.  The following calculations were made:  Between 700° and 1,000°, CO₂+Fe₃C=3Fe+2CO-14.5 cal.; 3Fe+C=FeC-27.5 cal.