| Magnetic fluids,due to their normal liquid behaviors coupled with magnetic properties,offer applications in many fields,such as chemical industry,instrument industry,machinery industry and biological medicine industry.Because this kind of functional material is often used in a magnetic environment,the stability and magnetic properties are recognized as crucial for the operating life and service performance.As a result,preparation of high stable magnetic fluids used in different working environment has been focused much attention.Besides,optimizing the current preparation process of magnetic fluids,or offering a novel producing method to solve the problem that the surfactants often have a week pinning effect on the surface of magnetic particles,is another research interest.In the present thesis,liquid Ga-based magnetic fluids which are supposed to available in a high temperature environent was prepared by different processes,and the influence of preparation process on the stability and magnetic properties of liquid Ga-based magnetic fluids has been studied.TEM,VSM,EDS,XRD and GMB were used to characterize the magnetic particles and magnetic fluids.By using the TEM technology,a coating layer was observed on the surface of Ni nanoparticles after a coating process.The coating layer was then verified as Al2O3 by an EDS analysis.As a result,it is concluded that Al2O3 has been coated on the Ni nanoparticles.When improving the stability of liquid Ga-based magnetic fluids by a coating method,it is verified that Al2O3 is more suitable to use as the coating material than SiO2,liquid Ga-based magnetic fluid with Al2O3-coated Ni perform good stability and saturation magnetization.When improving the stability by a heat treatment method at 573 K,liquid Ga-based magnetic fluids also perform good stability,in spite of the decrease of saturation magnetization.The mechanisms of this two kinds of surface treatment technologies were discussed,the decrease of saturation magnetization of liquid Ga-based magnetic fluids after a 573 K heat treatment was due to the fact that part of Ni nanoparticles have reacted with liquid Ga and their magnetic property thus lost.Besides,a novel method of preparing magnetic fluids was discussed in this thesis.n-Hexane as the oil-phase,Brij-30 as the emulsifier and mixed solutions of Fe2+ and Co2+ as the water-phase were used to prepare microemulsion-based magnetic fluid.Study found that when the concentration of the mixed solutions of Fe2+ and Co2+range between 1.0 M and 1.2 M,the concentration of NaBH4 solution is 2 M and the volume ratio of each component is in accordance to Vn-Hexane:Vwater solution:VBrij-30=9:3:3,the as-prepared microemulsion perform good stability.Water/n-hexane based ferrofluid with FeCoB magnetic nanoparticles produced based on this kind of microemulsion shows great magnetic properties,with saturation magnetization of 4.9 emu/g and remanence and coercivity of almost to zero.The as-prepared water/n-hexane-based ferrofluid features perfect stability and recoverability,and the resilience coefficients at the magnetic field strength of H=110 mT and H=210 mT are 71.2%and 65.4%respectively.Furthermore,the as-prepared water/n-hexane-based ferrofluid has good magnetoviscous effect and magnetic responsibility,and its logarithmic value of viscosity without external magnetic field is equal to 0.75,while the logarithmic values increase to 3.2 and 4.5 when at the external magnetic field of 500 Gs and 1100 Gs respectively.Finally,the preparing process of the water/n-hexane-based ferrofluid with FeCoB magnetic nanoparticles was optimized.Span-80 and OP-10 were selected as the emulsifiers of preparing water/n-Hexane microemulsion,and the experiments demonstrate that when the volume ratio of each component is in accordance to Vn-Hexane:Vspan-80:VOP-10:Vwater solution=14:3:3:6,the as-prepared water/n-hexane-based ferrofluid shows not only great long-term stability at external magnetic field but also increased saturation magnetization with its value of 12.9 emu/g. |
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