Influence Of Sio_2 And/or Mno_2 On The Reduction Behaviour And Structure Changes Of Fe_2o_3 Compacts With Co Gas

摘要

Pure Fe_2O_3 and Fe_2O_3 doped with either 2.5-7.5 mass% SiO_2, 6.0mass% MnO_2 and (6.0%MnO_2+ 7.5%SiO_2) compacts annealed at 1 473 K for 6h were prepared. The different phases were identified by X-ray diffraction (XRD) and their structures were examined by optical and scanning electron microscopes. The magnetic properties were measured with Vibrating Sample Magnetometer (VSM). Total porosity and pore size distribution were determined and their external volume was also measured. Unlike in SiO_2 doped samples where no new phases were detected, manganese ferrite (MnFe_2O_4) was identified in MnO_2-containing samples. Annealed compacts were isothermally reduced with CO at 1 073-1 373 K and the O_2-weight loss was continuously recorded. It was found that the reduction rate of SiO_2-Fe_2O_3 samples increases at the early stages with SiO_2 mass% due to the increase in their original porosity. At final stages, the rate was retarded due to the formation of hardly reducible fayalite (Fe_2SiO_4). In MnO_2-containing samples, the reduction rate was retarded at initial stages due to the presence of manganese ferrite. At later stages, the formation of fayalite-manganoan [(Fe, Mn)_2SiO_4] greatly hindered the reduction process. A catastrophic swelling (ΔV= 405%) was recorded in 6%MnO_2-Fe_2O_3 compacts and was greatly diminished to 55.95% in presence of 7.5% SiO_2 due to the decrease in size and number of metallic iron whiskers and plates. The reduction mechanism of pure and doped samples was predicted from the correlations between reduction kinetics and the microscopic examinations of partially and completely reduced samples.