Synthesis And Characterization Of Magnetite Microspheres

Magnetite is one of the most important functional materials. The preparation and characterization of Fe3O4 microspheres have become a hot topic in the field of nanomaterial for there good potential application in areas such as biomedical, catalyst and microwave absorption. Researchers have been trying to improve their performance of application by controlling of the morphology and structure of Fe3O4 microspheres. In this paper, we prepare Fe3O4 microspheres both with and without template, and explore how reaction conditions affect the morphology and structure of microspheres. In addition, electromagnetic properties of the microspheres are characterized. The main contents of this paper can be summarized as follows.(1) Fe3O4@MF microsphere with particle size of about 2 μm was synthesized with melamine formaldehyde resin as template. By means of scanning electron microscopy, infrared spectroscopy and thermo gravimetric analysis, the coating mechanism of Fe3O4 was explored, and the coordination between aminoes and ferrous irons was found to play an important role in it. The effects of temperature and concentration of ferrous ion on the phase of the microspheres were investigated by means of X-ray diffraction and Mossbauer spectroscopy. It was observed that the purity of phase increase with the increase in the concentration of absoption. Among the samples prepared at different temperatures, the sample prepared at 60℃ has the best purity. Characterized by vibrating sample magnetometer on magnetic microspheres, the change of the saturation magnetization against reaction conditions was analyzed and it was found the values of saturation magnetization are closely related to the amount of coated layer and the phase purity.(2) The Fe3O4@MF microspheres were modified by hydrazine reduction, nickel ion incorporation and coated silica. It was found that hydrazine can effectively reduce the amount of weak magnetic substance α-FeO(OH) in the coating magnetic layer, and a substantial increment was observed in the saturation magnetization of the sample after the reduction. The addition of nickel ions in the adsorption process can effectively increase the amount of the magnetic material in the coating layer, which effectively improves the saturation magnetization of the composite microspheres. Besides, it was found that the introduction of silicon dioxide is not conducive to the enhancement of the saturation magnetization of the sample.(3) A series of Fe3O4 microspheres with radius of about 500 nm was prepared with ferric chloride, ethylene glycol and ammonium used as raw materials were prepared in a template free condition. By adjusting the reaction temperature, microspheres with different percentage of hollow structure were obtained. The sample MT170 which was systhetised at 170℃ is a solid one. The samples synthetized in the temperature range of 175--190℃ are partially hollow microspheres. The sample synthetized at 200℃ is composed of completed hollow microspheres. Besides, part of microspheres in MT250 which was synthetized at 250℃ have broken up. The obtained samples all have high purity and good crystallinity. Through the refinement of XRD spectra, the grain sizes and the lattice constants of the samples were got. The behaviors were found that the grain size of the samples decreases linearly with the decreasing of the reaction temperature and the lattice constant increases at first then decreases with the increase of reaction temperature. Mossbauer spectrums with distribution in the hyperfine filed of B site are fitted. The results of fitting show that the distribution becomes larger with the decrease of reaction temperature and the ratio of area of A to area B increases with the decrease of the reaction temperature. Based on the theory that vacancy prefers to occur at feerous iron in B site, the concentration of iron vacancy was calculated. It was found that the concentration increase with the decrease in reaction temperature. The concentration of iron vacancy in MT250 and MT170 are 0.023 and 0.122, respectively. Besides, the effects of the hollow structure, grain size and the concentration of the vacancy on the static magnetic properties were analyzed. In addition, the effect of vacancy concentration on electromagnetic performance was explored by means of network vector analyzer, and the phenomenon that the real part of permittivity and the imaginary part of permeability decreases with the increasing vacancy concentration in the frequency band of 2--18 GHz is found. The reflection losses of the coatings on a metal flat prepared by different vacancy concentration samples were calculated, and the reflection loss peaks were found to increase with the increasing of vacancy concentration.