EFFECT OF SNO2 ADDITION ON REDUCTION INHIBITION OF ALPHA-FE2O3

Reduction behavior of alpha-Fe2O3 containing SnO2, Al2O3 or Cr2O3 unde r low oxygen pressure (nitrogen atmosphere) was investigated by the th ermogravimetry. alpha-Fe2O3 powders mixed with 1-10 mol% SnO2, 5 mol% Al2O3 or 5 mol% Cr2O3 were pressed, sintered at 1250 degrees C for 10h , and then crushed. 5 mol% Al2O3 and 5 mol% Cr2O3 made solid solutions with alpha-Fe2O3, and SnO2 was estimated to dissolve up to about 9 mo l% at 1250 degrees C for 10h. Pure alpha-Fe2O3 was reduced between 115 0 and 1300 degrees C. The reduction behavior of alpha-Fe2O3 with 5 mol % Al2O3 or 5 mol% Cr2O3 was similar to that of pure alpha-Fe2O3, and t here was no effect of Al2O3 or Cr2O3 addition on the reduction inhibit ion of alpha-Fe2O3. On the other hand, the onset temperature and the o ffset temperature of weight loss for alpha-Fe2O3 with SnO2 increased w ith increasing SnO2 content. The activation energy for the reduction r eaction of alpha-Fe2O3 was calculated to be about 633 kJ/mol by Ozawa method, and this value coincides with the activation energy for oxygen diffusion in alpha-Fe2O3. Therefore, it is considered that the reduct ion reaction of alpha-Fe2O3 was controlled by the oxygen diffusion, Th e reduction inhibition of alpha-Fe2O3 by SnO2 addition has been explai ned by the suppressed creation of oxygen ion defects responsible for o xygen ion diffusion.