2248.     MEYER, H. H.  [Speed of Reduction of Iron Ores in Flowing Gases.]  Mitt. Kaiser Wilhelm Inst. Eisenforsch. Düsseldorf, vol. 10, 1928, pp. 107-116.  Chem. Abs., vol. 23, 1929, p. 1371.

        At 650° the ores reduced in H₂ begin to sinter, and H diffuses less readily to the center of the kernels.  As a result, the speed of reduction falls rather sharply.  At 900°, the speed is again accelerated, since H diffuses more rapidly into the γ-Fe.  In CO, sintering is effectively prevented by the separation of C.  The speed of reduction, however, is slower than with H₂ so long as there is no sintering.  For technical purposes a mixture of CO and H₂ is very effective, because of the reactivity of the H₂ and the prevention of sintering by the CO.  Magnesite reduces chiefly on the surface, and the higher the temperature the greater must the degree of reduction be before C is set free.  The presence of H₂ promotes C formation.  With minette (Fe silicate) the phenomena are the same, but because of its greater porosity the reduction is more rapid.  Likewise the separation of C in the interior of the kernel tends to break it up.  Above 1,000° silicates are formed that close up the pores and retard the reaction.  Where no sintering occurs the speed of reduction is about 4 times greater with H₂, and in both cases the speed is proportional to the surface of the ore and the concentration of the gas, the reaction velocity constant being d/D, where d is the diffusion coefficient and D is the thickness of the adsorbed gas layer.  The temperature coefficient of the speed of reaction is consequently quite small.  In H₂-CO mixtures, the CO does not appear to reduce directly, but converts the H₂O formed into H₂ and CO₂.

        MEYER, K.  See abs. 988, 989, 990, 991, 992, 993, 1048, 2622, 3070, 3071, 3072.