Preparation And Stability Mechanism Of Alkalescence Water-based Fe₃O₄Ferrofluid

Ferrofluid can behave many special excellent performances under the action of magnetic field due to the combination of magnetism and liquidity, which showing a good application prospect in the fields like electronic information, aerospace, precision manufacturing and bio-medical aspects. In this paper Fe3O4magnetic nanoparticles were prepared by chemical co-precipitation method, then manufactured into water-based ferrofluid after coating by sodium oleate. All the samples were characterized by measurements, such as XRD, SEM, TEM, FT-IR, VSM and so on. Analysis many factors that played effects on Fe3O4magnetic particles and magnetic fluid properties in the manufacturing and modifying process, and focus on coating structure and stability mechanism of magnetic nanoparticles in ferrofluid.Firstly, Fe3O4magnetic nanoparticles were prepared by chemical co-precipitation method. Discussed influences including precipitation agents, reaction temperature, pH value, crystallization time and other factors on the product particle size, crystal structures and magnetic properties, thus optimal technological conditions of manufacturing Fe3O4magnetic nanoparticles was obtained. Fe3O4samples which were made from the improved method were characterized, it turned out that Fe3O4particles possess nverse cubic spinel phase structure, irregular appearance of spherical and uniform particle size distribution, the average Fe3O4particles size is13～18nm and extremely easy to reunite. The product possess superparamagnetism, besides that saturation magnetic field is at around5000Oe and saturation magnetization is62.7emu/g.Studies of the stress condition of magnetic nanoparticles in the ferrofluid show the condition of ferrofluid possesses sedimentary stability is that the size of nano-magnetic particles is enough small, the kinetic energy thermal motion is strong enough to overcome the sedimentation by the gravitational field and the diverse magnetic field. The condition of ferrofluid possesses dispersion stability is that action between particle surface double electrode layer repulsive force and surfactant layer steric hindrance enough overcome the aggregation caused by van der waals and magnetic force.The obtained Fe3O4magnetic nanoparticles were used to prepared water-based ferrofluid after deionization and using sodium oleate as surfactant. Factors which affected magnetic fluid stability were discussed, including deionization disposal, surfactant agents, coating temperature and time. The obtained magnetic fluid has a good stability in alkalescence system, from analysis we know that sodium oleate formed double-layer coating on Fe3O4particles surface, the first layer is firm chemisorptions, combined in bridge type coordination structure by carboxylate radical of sodium oleate and surface of Fe3O4magnetic particles, the second layer is physical absorption, steric hindrance of surfactant coating layer and electrostatic repulsion of magnetic particles, both function maintain the magnetic fluid stability.