In Situ Observation of Reduction Behavior of Hematite with Solid Carbon and Crystallographic Orientation between Hematite and Magnetite

Abstract

Recently, the composite pellets between iron ore and carbon are studied by many researchers because of its high reactivity. However, the reaction mechanism of the composite pellet is not yet clarified. It is obviously determined the reaction mechanism at initial stage as the direct reaction between solid carbon and iron oxide. However, in the course of reaction, the reaction mechanism will change to the indirect reduction of iron oxide with CO gas owing to the separation of the interface between solid carbon and iron oxide.
In this study, samples of polycrystalline hematite (grain size was approximately 20 μm) were prepared. The hematite sample was coated by carbon with different thickness. The in situ observation by a laser microscope was carried out. The crystal orientation and morphology was investigated before and after the reaction using EBSP, SEM, AFM, XRD and Raman.
The direct reduction began from about 650°C and the reaction proceeded rapidly until carbon was consumed. The behavior of reduction was different from the thickness of carbon layer (amount of carbon) which was related to whether the product gas (CO) could be passed through the carbon layer or not. After reduction, the lath magnetite having same direction was a grain was observed on the surface. The crystallographic orientation between magnetite and hematite was as follows;
(0 0 0 1)_H || (111)_M, [1 1 0 0]_H || [110]_M
In addition, the growth direction of the lath magnetite formed on the hematite surface was
[2 1 3 0]_H || [101]_M