The Preparation And Characterization Of Magnetic Nanoparticles And Magnetic Fluids

(1) Fe₃O₄nanoparticles were prepared by co-precipitation method. N-oleoylsarcosinewas used to modify the Fe₃O₄nanoparticles to improve the compatibility between theFe₃O₄nanoparticles and the carried liquid. The optimal reaction conditions such as thedose of surfactant, reaction temperature and reaction time, pH were studied and the optimalconditions were determined. Stable poly alpha olefin （PAO） based magnetic fluid （MF）was obtained through phase transfer method. The stability difference between the MFprepared with the present method and the MF prepared with the traditional method wasalso compared. The particle morphology, crystal structure and magnetic properties wereinvestigated. The magnetism and stability of the PAO-based MF were characterized byGouy magnetic balance, and rheological properties of the PAO-based magnetic fluid werealso investigated.（2） The Mn-Zn ferrite nanoparticles were prepared by chemical co-precipitation usingFeC13·6H2O, MnSO₄·H₂O and ZnSO₄·7H₂O as the starting materials. During theco-precipitation, the effects of the ratio of Mn²⁺and Zn⁽2+_concentration on the magneticproperties were considered. To prevent the aggregation of nanoparticles,trimethoxyhexadecylsilane was used as surfactant, the heat transfer oil based magneticfluid was also prepared through phase transfer method. The particle morphology, crystalstructure and magnetic properties were investigated. The interaction between the Mn-Znferrite nanoparticles and trimethoxyhexadecylsilane was characterized using Fouriertransform infrared （FT-IR） spectroscopy. The stability and magnetic properties werecharacterized using magnetic balance.（3） Perfluoropolyether based magnetic fluid was prepared using tetraethoxysilaneand fluorocarbon surfactant as modifier. To improve the interaction between the Fe₃O₄nanoparticles and the fluorocarbon surfactant, the Fe₃O₄nanoparticles were firstly coated with a SiO2layer by the hydrolysis of tetraethoxysilane. The optimal amount oftetraethoxysilane and fluorocarbon surfactant was determined. The properties of the Fe₃O₄nanoparticles and the perfluoropolyether based magnetic fluid were investigated. Theresults indicated that the Fe₃O₄nanoparticles had well crystal structure, uniform particlesize and high saturation magnetization. The perfluoropolyether based magnetic fluid hadstrong magnetism, high stability and sheer thinning property.