Research On Preparation, Characterization And Cobalt Modification Of The γ-Fe₂O₃ Nanopowder Throught Solid-state Reactions

The precursor ofγ-Fe₂O₃ nanoparticles is synthesized with FeSO₄·7H₂O and H₂C₂O₄·2H₂O through solid state reaction at ambient temperature. The structure and the morphology of precursor are studied by X -ray diffraction (XRD) and transmission electron microscope (TEM). The effect of the processing technology and the mol ratio on the precursor yield are also discussed. The results indicate that grinding the reagents respectively and grinding the reagents mixture with the mol ratio 1.2:1 of H₂C₂O₄·2H₂O and FeSO₄·7H₂O can get a perfect yield.The precursor is annealed at different temperature for 3 hours and the analysis of the products structure and morphology indicates that the well-proportionedγ-Fe₂O₃ nanoparticles with about 30nm particle size is obtained through annealing the precursor at 450℃for 3 hours.The activate energy of growing is Ea = 18.965k J /mol obtained through analysis the relationship of the annealing temperature and the particle size. When the annealing time increases from 0.5 hours to 20 hours at 450℃, the average particle size increases from 10nm to 70nm. The process of growth accord with the G-M grain growth kinetics model and can be divided into the fast growth process (0.5-6 hours) and the slow growth process (6-20 hours). The kinetics equation of the fast growth process and the slow growth process are, The G-M crystal growth kinetics model indicates that the surface diffusion is the major mechanism at the fast growth process and the body diffusion is the major mechanism at the slow growth process at 450℃.The XRD and FTIR research of theγ-Fe₂O₃ nanoparticles indicates that the nanoparticles exhibits blue shift and the lattice exhibits lattice expansion as the particle size decrease. The reason of these phenomenon are discussed.The particle size, stability, lattice distortion and the FTIR ofγ-Fe₂O₃ nanoparticles by doping cobalt element are researched. A new phenomenon is discovered that doping cobalt element can restrain the form ofα-Fe₂O₃. All the XRD diffraction patterns turn narrow and the lattice exhibits lattice constriction as the doping mol contents increase. The FTIR of theγ-(Fe_1-xCo_x)₂O₃ nanoparticles exhibit blue shift and the wavenumbers of the Fe-O bond turn larger as the doping cobalt element mol percentage increases(1—7mol.%).