Microstructural changes on the reduction of hematite to maanetite

The microstructures resulting from the reduction of hematite to magnetite have been examined for a wide range of temperatures and gas conditions. A transition in product morphology from plate or lath magnetite to porous magnetite was found to occur at a constant free energy difference between the reducing gas mixture and the hematite over a range of reaction temperatures. Direct observations of lath nucleation and growth are reported and show the self-accelerating effect of the Fe₂O₃ → Fe₃O₄ transformation. The limits of porous growth are discussed in terms of established theories of discontinuous precipitation and a mechanism for the formation of lath magnetite is proposed.