Characterization of γ-Fe2O3 nanoparticles prepared by transfor- mation of α-FeOOH

γ-Fe2O3 nanoparticles were successfully synthesized by a chemically induced transformation of α-FeOOH. In this method, the precursor （α-FeOOH） was prepared by chemical precipitation, and then treated with a mixed FeC12/NaOH solution to produce the nanoparticles. X-ray diffraction indicated that when the precursor was treated with FeCl2 （0.22 mol/L） and NaOH （0.19 mol/L）, pure γ-Fe2O3 nanoparticles were obtained. However, when the concentration of FeCl2 was 〈0.22 mol/L or the concentration of NaOH was 〈0.19 mol/L, α-FeOOH and γ-Fe2O3 phases co-existed in the nanoparticles. Transmission electron microscopy observations showed that in the samples with co-existing phases, the nanoparticles did not have identical morphologies. The pure γ-Fe2O3 nanoparticles were polygonal rather than spherical. The volume ratio of α-FeOOH and γ-Fe2O3 was estimated for the two-phase samples from magnetization data obtained from a vibrating sample magnetometer. This chemically induced transformation is novel, and could provide an effective route for the synthesis of other metal oxide nanocrystallites.