De Cai Li

Preparation and Characterization of Fe3O4@Au Nanoparticles Used as Precursor of Ferrofluids

The Fe3O4 magnetic nanoparticles were prepared through co-precipitation of Fe3+ and Fe2+ with ammonium hydroxide. The initially obtained Fe3O4 nanoparticles were then coated by gold in solution of chloroauric acid through connecting of 3-aminopropyropyl thriethoxysilane (3-APTES) and the obtained Fe3O4@Au nanoparticles were further characterized by X-ray photoelectron spectrum (XPS). During the process, the influences of chloroauric acid, reducing agent, coupling agent and nanoparticles of Fe3O4 were studied. The results showed that core-shell structure Fe3O4@Au particles have diameters of about 20nm in size synthesized from sodium citrate as reducing agent with 10.08 emu/g of saturation magnetization.

Experimental Study on the Second-Order Buoyancy of Magnetic Fluid

The buoyancy principle of magnetic fluid is one of the most attractive effects of magnetic fluid statics. But it is too difficult to calculate the buoyancy directly due to the complexity of magnetic field. Moreover, numerical calculation employs too many assumptions. So in this paper the experimental method is adopted to measure the second-order buoyancy received by permanent magnet immersed in magnetic fluid, which depends on the distance between the magnet and the wall of vessel. The influence of the diameter of cylindrical vessels, the size of magnets and the saturation magnetization of magnetic fluid on the buoyancy is also analyzed qualitatively.

The Experimental Study of the Magnetic Fluid Damper Based on the Principle of Second-Order Buoyancy

Two different structure of dampers based on the principle of second-order buoyancy were designed in this paper. In order to verify the reduction of the vibration, a test rig was set up. On the test rig, the reduction effect of two different dampers was studied by adjusting the amount of the magnetic fluid. The experiment results indicate the relationship between the damping effect of magnetic fluid damper and the amount of magnetic fluid and this analysis result is benefit to the design of the dampers.

Study on Magnetic Fluid Static Seal of Large Gap

Researchers have been studying the magnetic fluid seal of small gap in the past. In order to meet the static seal requirements of large gap in aviation, aerospace, metallurgy, and so on. We set up the experimental rig of magnetic fluid static seal and designed the static seal of magnetic fluid. In the experimental rig, we studied the static seal of magnetic fluid and obtained the relationships among the burst pressure and the amount of injection of magnetic fluid, seal gap, temperature and magnetization in the experimental rig. In theory, we calculated the distribution of magnetic field under the seal gap and reasoned sustained pressure and temperature and calculated the burst pressure in different gaps and different saturation magnetization. We analyzed the experimental and theoretical results in detail. The theoretical analysis and tests indicated that magnetic fluid seal of large gap and large diameter can sustain a definite pressure and meet the requirements of practical problems.

Structure Design of Magnetic Fluid Static Seal at Large Diameter Flange

In order to meet the requirements of the static seal at large diameter in chemical industry, aerospace industry and military industry, we designed a magnetic fluid static seal at large diameter flange and set up a test rig. We studied the effect of magnetic fluid static seal on the test rig. Finally, we obtained the relationship between the anti-pressure capacity and the number of the seal stages. We also calculated the distribution of the magnetic field in the seal gap and the anti-pressure capacity in theory. The theoretical analysis and the experiment result indicate that the design of the magnetic fluid static seal at large diameter flange is feasible and can be used to meet the practical problems.

The Comparison of Magnetic Leakage of Different Teeth Structures in Magnetic Fluid Seal

Based on the theoretical model, magnetic field distribution of rectangular teeth, two-sides dilated shape and one-side dilated shape teeth structure with common other conditions were calculated using finite element method when the sealing gap was 0.1mm and 0.12mm. The comparison of their results with the same sealing gap showed that rectangular teeth structure had the highest magnetic leakage. Moreover, the magnetic field distribution of sealing structures with rectangular stages on both the shaft and pole pieces under the same design and sealing gap were also calculated using the same method, whose result was compared with rectangular stages on pole pieces only. The comparison showed that the former did not have higher pressure capability obviously but led to higher magnetic leakage.

The Analysis of Pressure Capability of Different Teeth Structures in Ferrofluid Seal

Theoretical model of calculating magnetic field of typical ferrofluid sealing structures with magnetic vector potential method is built. Based on the theoretical model, magnetic field distribution of rectangular teeth, two-sides dilated shape and one-side dilated shape teeth structures with common other conditions were calculated using finite element method when the sealing gap was 0.1mm and 0.12mm. The comparison of their results with the same sealing gap showed that one-side dilated shape teeth structure had higher pressure capability than other shape teeth under reasonable design.

Study on Magnetic Model and Magnetic Force of Magnetic Fluid in Pressure Difference Sensor

Magnetic fluid is the key core of magnetic fluid sensor. Here magnetic model of magnetic fluid is analyzed. The magnetic curve of magnetic fluid is divided into 3 parts and the liner area is presented to make magnetic fluid sensor more sensitively. The magnetic force of magnetic fluid in magnetic field is calculated and analyzed. The magnetic permeability of magnetic fluid in sensor could be treated as a constant in the linear area of magnetization curve. And the magnetic force of magnetic fluid in magnetic field could be ignored if the length to diameter ratio of the solenoid is large enough.

Preparation and Characterization of Diesel Fuel-Based Magnetic Fluids

Among different types of magnetic fluids, diesel fuel-based magnetic fluids have a high application value because of low viscosity, low volatile and cheap carrier liquid. In this paper, Fe3O4 nanomagnetic particles were prepared, optional technological conditions were determined. It was that concentration of the reactors was 0.6mol/L, reaction temperature was 70°C and reaction time was 1h. Then it was found that the appropriate coating time for surfactant was 4 hours. The particles prepared under this process had the high saturation magnetization and preferable dispersibility. Finally by ultrasonic oscillating combined with mechanical raking, diesel fuel-based Fe3O4 magnetic fluids were prepared.

Study on Magnetic Liquids Properties for Sensor Design

The physical properties of magnetic liquids are theoretically analyzed in this paper, such as the effect of the magnetic volume force on the free surface of magnetic liquids, the density spectrum of the magnetic liquids based on horizontal component of the magnetic volume force, the first order levitation principle and the second order levitation principle, the magneto-electric principle of magnetic liquids, the fluidity of magnetic liquids used as magnetic core and the fluxgate effect of magnetic liquids. Some methods to study the properties of magnetic liquids were provided by the authors, and the effects of the magnetic volume force on the free surface of magnetic liquids and the second order levitation effect were experimentally studied in this paper. The analysis methods that provided in this paper may be applied to the design of new sensors.