Morphology of hematite to magnetite reduction zone

The reduction process of hematite to magnetite results in distinct changes in morphology of magnetite. These changes depend on structural properties of parent hematite and reduction conditions. The reduction experiments were performed in 3% CO and 97% CO2 gas mixture at 450 and 850°C on selected crystals of natural hematite. The phase composition and morphological characteristics of the reduced layer were determined on the basis of microscopic analysis. Singular blasts or blastoidal colonies of magnetite were formed in 450°C on the boundaries of the hematite grains. They began to grow and joined the layer. Magnetite formed at 450°C is distinctly microporous. Cracks and desintegration of hematite grains appear together with reduction of hematite. At 850°C nucleation of the magnetite is quite different then at 450°C. The formation of singular magnetite lamellae or a palisade of crystallographically oriented magnetite lamellae were observed. Their growth results in the formation of the magnetite layer. Tunnel‐shaped pores in magnetite layer show the same direction as lamellar front of reduction.