Quantitative analysis on contribution of direct reduction of iron oxide in carbon composite

Many reactions such as the reduction of iron oxide, gasification of carbon, and so on occur simultaneously during heating of the iron oxide-carbon composites which attract attention as "microreactors". Solid carbon and CO gas react with iron oxide via direct and indirect reductions, respectively. The rate of indirect reduction has been studied extensively. On the other hand, there are very few reports on the quantitative analysis on the direct reduction due to analytical difficulties, although it is important to understand the total reduction mechanism in detail. In this study, the contribution of the direct reduction by solid carbon in the composite while heating at a constant rate under inert gas flow was quantitatively evaluated. The direct reduction from Fe₂O₃ to Fe₃O ₄ proceeds at a low temperature during heating of the Fe ₂O₃- graphite composite. When the reduction from Fe ₂O₃ to Fe₃O₄ completes below 1 000°C, the contribution ratio of the direct reduction in the total reduction is approximately 45%. However, there is no effect of the particle size of the raw materials on the contribution ratio. Further, the contribution ratio of the direct reduction for the reduction from Fe₃O₄ to FeO is small.