Occurrence State of SiO_2 in Hercynite Synthesized by Reaction Sintering

Sample was prepared using Fe2O3, Al2O3 and Si O2 powders as raw materials according to mass ratio Fe O:Al2O3 of 40.8:59.2 and adding a percent of Si O2 in the synthetic system, and being sintered under high purity nitrogen atmosphere at 1 600 ℃for 4 h. The sample was analyzed and characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and transmission electron microscope. Based on Fe O-Al2O3-Si O2 ternary phase diagram, the existence of silicon dioxide was investigated. The results indicate that silicon dioxide didn't enter into hercynite crystals, but existed among hercynite crystals as amorphous phase. When a percent of Si O2 was added into the synthetic system, amorphous phase containing Si O2 was discontinuously distributed and the direct contact among hercynite crystals wasn't changed.