1088.    FRICKE, R., WALTER, K., AND LOHRER, W.  [Effect of the Physical State of the Solid Reactants on the Equilibrium Fe/Fe₃O₄ with H₂O/H₂.]  Ztschr. Elektrochem., vol. 47, 1941, pp. 487-500; Chem. Abs., vol. 36, 1942, p. 4010.

       Below 500°, Fe reacts with steam according to the binary equilibrium, 3Fe+4H₂O=Fe₃O₄+4H₂; above 570°, FeO is first formed, and from this Fe₃O₄.  The equilibrium was measured at a constant steam pressure, so that the only variable was the pressure of the H₂.  Calorimetric data and specific heats indicate that at 525° the heat of reaction is greater for active Fe than for ordinary Fe by about 22.6 kcal.  An x-ray examination of active Fe at 450° indicate an average particle size of 275 Å., and for inactive Fe 470 Å.  The increase in the heat of reaction when active Fe is used is due to the increased heat content.  Owing to large differences in the surface of the Fe particles, x-ray results are not sufficient to account for the large differences in the heat of reaction.  This may be due to the fact that x-ray values are always average values, whereas only the more active particles are involved in equilibria.