Effect of SnO2 Addition on Reduction Inhibition of α-Fe2O3

Reduction behavior of α-Fe2O3 containing SnO2, Al2O3 or Cr2O3 under low oxygen pressure (nitrogen atmosphere) was investigated by the thermogravimetry. α-Fe2O3 powders mixed with 1-10mol% SnO2, 5mol% Al2O3 or 5mol% Cr2O3 were pressed, sintered at 1250°C for 10h, and then crushed. 5mol% Al2O3 and 5mol% Cr2O3 made solid solutions with α-Fe2O3, and SnO2 was estimated to dissolve up to about 9mol% at 1250°C for 10h. Pure α-Fe2O3 was reduced between 1150 and 1300°C. The reduction behavior of α-Fe2O3 with 5mol% Al2O3 or 5mol% Cr2O3 was similar to that of pure α-Fe2O3, and there was no effect of Al2O3 or Cr2O3 addition on the reduction inhibition of α-Fe2O3. On the other hand, the onset temperature and the offset temperature of weight loss for α-Fe2O3 with SnO2 increased with increasing SnO2 content. The activation energy for the reduction reaction of α-Fe2O3 was calculated to be about 633kJ/mol by Ozawa method, and this value coincides with the activation energy for oxygen diffusion in α-Fe2O3. Therefore, it is considered that the reduction reaction of α-Fe2O3 was controlled by the oxygen diffusion. The reduction inhibition of α-Fe2O3 by SnO2 addition has been explained by the suppressed creation of oxygen ion defects responsible for oxygen ion diffusion.