| The magnetic fluid is a colloidal solution that consists of magnetic nanometer particles coated with surfactants and a base liquid. It is a kind of magnetic material in which the nanometer magnetic particles are dispersed in the base liquid homogeneously. It has a series of distinctive and excellent properties different from that of the other magnetic materials, because the magnetic fluid has flow ability and superparamagnetism. It is important in high-tech materials and widely used in the field of high and new-type technology such as aviation and space flight, electronic technology, chemical industry, information technology, biology and medicine, etc.The water-based Fe3O4 magnetic fluid contening of electrolytes has been prepared with coprecipitation method and the property of counter-electrolyte has also been studied. A special arts and crafts preparing Fe3O4 magnetic fluid contening of electrolytes has been designed. The theories and technologies of surface and colloid chemistry, magnetism and material science have been used in the preparation of water-based Fe3O4 magnetic fluid. The tow methods of controlled partial reduction method (CPRM) and coprecipitation of preparation of Fe3O4 nano particle was compared. It was found that the nano particles prepared by CPRM has a perfect size distributing but difficult to separate and the preparation process of magnetic fluid is more convient by the method of coprecipitation. The optimal conditions, including the best kind of surfactants and the proportion of surfactants, have been investigated. Meanwhile, the optimal preparation conditions of reactants have also been found by orthogonal experimental method. And the results, from the measurement of magnetic property, are almost identical.The influence factors of preparation of Fe3O4 magnetic fluid was studied in the reactant proportion, the reactant concentration, the reaction mode, the reaction temperature and the reaction time. Finally the excellent preparation conditions of Fe3O4 magnetic fluid are achieved. The experiment results show that, in the coprecipitation, the proportion of Fe2+ and Fe3+ is 2:3, the concentration of NaOH is 2mol·L-1, the reaction temperature is 55℃and the reaction time is 5.5h. The best pH and Zeta potential have been found by analysising the static and steric mechanism of Fe3O4 colloid based on the Stern Double Layer theory. The sodium tripolyphosphate (STPP) has been used to modify the Fe3O4 nanoparticles first and the sign of Zeta potential changed from positive to negative. More Fe2+ have been congregated around the Fe3O4 nano particles by the chelate ability of STPP. So the Fe3O4 nanoparticles have a stronger oxidation resistance. The surfactant Brij35 has been used as a steric modification to modify the product of the above. So the stable water-based stable Fe3O4 magnetic fluid obtained under the static and steric effect of the surfactants.The conductance of water-based Fe3O4 magnetic fluid has been measured. The result shows that the conducatance of the system is 4.0mΩ-1 and it is 5~7 times of conductance of the Fe3O4 water suspension. The result shows that the system contenting more electrolyte than the traditional products.In a word, the operation process of preparation of water based Fe3O4 magnetic fluid by means of coprecipitation is simpler than the tradition method. The average particle diameter of Fe3O4 magnetic fluid is about 37.8nm and the Fe3O4 magnetic fluid has excellent stability properties, good magnetism and counter-electrolyte ability.
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