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The Study Of Synthesis And Properties Of Magnetite And Magnetite-Composite Nanoparticles

Posted on:2011-08-09Degree:MasterType:Thesis
Country:ChinaCandidate:J W DongFull Text:PDF
GTID:2121360305465411Subject:Materials Physics and Chemistry
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This paper is mainly focused on the study of the structural, morphological, and magnetic properties of magnetite nanoparticles and magnetite-composite nanoparticles.(1) Magnetite nanoparticles are synthesized by the coprecipitation method. The structural, morphological, and magnetic properties of the magnetite nanoparticles are characterized by X-ray Diffraction (XRD), Laser Confocal Raman Spectroscopy (LCRS), Scanning Electron Microscopy (SEM), and Vibrating Sample Magnetometer (VSM) respectively. The influence of surfactant concentration on the structural, morphological, and magnetic properties is studied. The thermal stability of magnetite nanoparticles is also discussed. The results show that surfactant concentration has no effect on the structural, morphological, and magnetic properties of magnetite nanoparticles; The structure of the magnetite nanoparticles is spinel, their magnetization and coercive force are almost zero, therefor they exhibit a superparamagnetic behavior; The magnetite starts to turn into maghemite at 200℃, maghemite then turn into hemite at 400℃.(2) Fe3O4@SiO2 composite particles are firstly prepared by modified Stober method and APTES is used to functionalize the surface of the composite nanoparticles with amino groups. The structural, morphological, and magnetic properties of the silica-coated nanoparticles are characterized by X-ray Diffraction (XRD), Fourier Transform Infrared spectrometer (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), and Vibrating Sample Magnetometer (VSM) respectively. Effects of the dispersity of magnetite colloid, the reaction temperature, the concentration of ammonia, the volume of TEOS, the volume of magnetite colloid on the structural, morphological, and magnetic properties of the Fe3O4@SiO2 composite particles are studied. The influence of amino-functionalized way on the morphological of the functionalized composite nanoparticles and the thermal stability of the composite particles are also discussed. The results show that the dispersity of magnetite colloid has a big influence on the morphologise of the composite particles; With the reaction temperature increasing, the composite particle size decreases and the composite particles turn into clusters from monodisperse particle; The monodisperse particle can be prepared only when the ammonia concentration is right; The coercivity and residual magnetization of the composite particles are nearly zero and therefore the composite particles hold a superparamagnetic behavior; The particle size and magnetic properties of the composite particles can be controled by changing the volume of TEOS and the magnetite colloid; The particles those are amino-functionalized in oil system have a better dispersity than that of water system; The structure of the composite particle is still spinel after 3 h heat treatment at 800℃, the thermal stability of the composite particles is better than that of the magnetite nanaoparticles.(3) Fe3O4@SiO2 composite particles are also synthesized by reverse microemulsion method (one-step and two steps method). Fe3O4@PS composite nanoparticles (oleic acid-coated magnetite colloid) and Fe3O4@PMMA composite nanoparticles are prepared through microemulsion polymerization as well. The influence of the w value (the molar ratio of water snd surfactant) on the TEOS hydrolysis in the two-steps method, different way of dropping on the morphological of the composite nanoparticles and the volume of monomer on the polymer encaosulation are studied. The results show that TEOS can not hydrolyze completely when the w value is small in two-method, the dispersity of the particles which made by one-step mechod is better compare to that of two-step mechod, the coercivity and residual magnetization of the composite nanoparticles are nearly zero, therefore they exhibit superparamagnetic behavior.
Keywords/Search Tags:coprecipitation method, magnetite nanoparticles, superparamagnetic, modified St(o|¨)ber method, Fe3O4@SiO2 composite nanoparticles, reverse microemulsion method, microemulsion polymerization, polymer-coated magnetitie nanoparicles
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