567.    CHUFAROV, G. I., AND TATIEVSKAYA, E. P.  [Reaction Zones in the Reduction of Magnetite and Hematite With Hydrogen.]  Acta Physiocochim, U.S.S.R., vol. 3, 1935, pp. 957-974; Chem. Abs., vol. 31, 1937, p. 4878.

      Reaction is autocatalytic.  The change in porosity with temperature and degree of reduction was studied and related to the reaction rate.  Magnetite is less porous than hematite, but below 600° the rate of reduction is faster.  Above this temperature the porosity and the rate of reduction decrease rapidly in both cases.  Microscopical investigations show the presence of the layers of a-Fe-Fe₃O₄ in the case of magnetite and a-Fe-Fe₃O₄-Fe₂O₃ in the case of hematite, while FeO could not be detected, and it is suggested that Fe₃O₄→Fe is the rate-determining process.  The rate of advance of the reduction zone is linear below 500° and the activation energy for hematite is 15,700 gm.-cal.