Effect of chloride ion on crystalline phase transition of iron oxide produced by ultrasonic spray pyrolysis

Abstract

Ultrafine spherical Fe2O3 powders with controllable morphology and crystal phase were synthesized by ultrasonic spray pyrolysis. In this experiment, we chose three common ferric salts (Fe(NO3)3·9H2O, FeSO4·7H2O or FeCl2·4H2O) as precursor solution and regulated the concentration of chlorine ion (Cl−) in precursor solution to produce Fe2O3 particles. The morphology, crystal structure and magnetic property of prepared Fe2O3 particles were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vibrating sample magnetometer (VSM). The diameter of the obtained Fe2O3 products ranged from 0.2 to 2 μm. And the product obtained from FeCl2 precursor solution was magnetic, which was composed of hexagonal α-Fe2O3 and cubic γ-Fe2O3 from XRD results. We also calculated the weight percent of α-Fe2O3 and γ-Fe2O3 in the product through XRD quantitative analysis. However, with the addition of Cl− in Fe(NO3)3 or FeSO4 precursor solution, the products turned from non-magnetic to magnetic, whose pure α-Fe2O3 phase became to α-Fe2O3 and γ-Fe2O3 multi-phase. Besides, the weight percent of γ-Fe2O3 and the amount of Ms increased with the Cl− concentration in precursor solution improving. According to the research, it can be inferred that the presence of Cl− inhibits the phase transition of γ-Fe2O3 to α-Fe2O3 at high temperature.