Effect of reducing gas on the volume change during reduction of iron oxide compacts

Iron oxide compacts fired at 1 373 K for one hour were reduced at 973-1 373 K using different reducing gases; namely CO, H-2 50%H-2-CO and simulated reformed natural gas. The reduction course has been followed up by means of recording weight-loss changes as a function of time. The structure of the compacts was examined by reflected light microscope whereas the volume change was measured by displacement method. II has been found that both temperature and reducing gas composition have a significant effect on the volume change behaviour during reduction. The volume change values of the completely reduced compacts were not well representing the volume change behaviour during reduction. The greater swelling was observed for compacts reduced with pure CO giving a maximum value of 224% for compacts reduced up to 90% reduction at 1 173 K. Reduction with pure H-2 showed a maximum contraction of 24% for compacts completely reduced at 1 123 K. The volume change behaviour for compacts reduced with gas mixtures was mainly dependant on the relative contents of CO and H-2 in the reducing gas. Mechanisms have been proposed for the volume change trends for compacts reduced with the different gases and correlated with the microstructure of the reduced compacts.