Effect of SnO₂ Addition on Reduction Inhibition of α-Fe₂O₃

Abstract

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.