A new thermogravimetric setup was developed to study direct reduction of iron oxide under well-controlled experimental conditions. Pure and industrial hematite samples were isothermally reduced by hydrogen and carbon monoxide gaseous mixtures. Influences of gas composition, gas flow rate, and temperature on reduction were investigated. Reduction rates obtained using the new setup were higher compared to conventional thermogravimetric method. This difference was due to the time required to replace the inert gas with the reactant gas in the conventional method, which led to lower reduction rate at the initial stage. Carbon deposited on the surface of the pellets at relatively high gas flow rates and at low temperatures. The presence of pure iron and high carbon potential in the gas phase were the cause for carbon deposition. Study of partially reduced samples illustrated that the outer layer of pellet with high iron content thickened as reduction proceeded inside the pellet. Closure of micro-pores and formation of dense iron phase in this layer decelerated diffusion of reactant and product gases, and led to decrease of reduction rate at later stages of reaction. At lower temperatures, this effect was coupled with carbon deposition. Therefore, the reduction was seriously hindered.
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