3625. WEIBERG, M. [Reduction of Iron Ores With Carbon Monoxide, Hydrogen and Methane.] Jernkontorets Ann., vol. 124, 1940, pp. 179-212; Chem. Zentralb., 1940, II, p. 3315; Chem. Abs., vol. 34, 1940, p. 6903; vol. 36, 1942, p. 6968.
Review of the equilibrium conditions in reductive Fe oxides with CO, H2, and CH4. The approximate relation between the O2 content of the wüstite region was calculated. On the basis of these calculations, the equilibrium diagram for the systems Fe-C-O and Fe-H-O were extended to include the O curves and the limits of the wüstite region in the phase diagram for the system FeO were corrected. Further, the relation between the equilibrium constants and the temperature was calculated for the reaction H2O+CO=H2+CO2 for temperatures up to 2,000° and for the reaction C+2H2=CH4 for temperatures up to 1,200°, as well as for the formation of CH4 by reduction with a mixture of CO and H2. IN the reduction with pure CO, the temperature increases about 100°-150°; in the reduction with pure H2, it drops about 350°. there is no change in temperature with a mixture of 64% CO and 36% H2. Reduction with CH4 or coke-oven gas requires addition of so much heat that it can only be carried out in a retort furnace or other equipment with special provision for supplying heat, unless the CH4 is first converted into a CO-H2 mixture by oxidation with O2, H2O, or CO2. Because of its greater rate of diffusion, H2 reduces more vigorously at 1,000° than CO until about 75% of the O contained in the ore has been removed. Beyond this point the reduction velocity with H2 drops considerably more rapidly than that with CO. Reduction time is shortest with a mixture of CO and H2. Microscopic investigations showed that the greater reduction velocity of CO toward the end of the reduction probably is due to its carbonizing action on the reduced Fe, which surrounds the remaining small grains of wüstite as a thin scale. As a result of the reaction between the C in the austentite and the O in the wüstite, a gas is formed under high pressure in the boundary region, which ruptures the Fe scale and permits further reduction by the CO. In reduction with H2, a similar condition may develop, except that only H2 and not H2O vapor is able to diffuse through the Fe scale, so that less excess pressure is developed in this case. In the reduction with pure CO at 1,000°, the Fe can be carbonized up to cementite, which does not show the constant composition Fe3C but rather possesses a certain solvent power for C or Fe so that if forms a homogeneous region in the phase diagram. Upon longer carbonization of reduced Fe at 1,000° with CO, the cementite disintegrates with the separation of C; a heavy deposition of C from the gas phase also takes place. Reduction of a pure magnetite crystal at 1,000° results in the formation of 3 layers; a nucleus of Fe3O4, an intermediate layer of wüstite, and a surface layer of pure Fe. This shows that the O2 passes through the wüstite layer by diffusion in solid solution; no porosity develops in the wüstite layer, only large fissures.