Study On Preparation Of Silicon Oil Based Magnetic Liquid

Magnetic liquid is a stable colloid.It is formed by magnetic nanometer particles that are coated by surfactant and dispersed in carrier liquid.Magnetic liquid is widely used in seals technology,lubricating technology,precise bearing technology and so on.Every year, there are thousands of magnetic liquid elements that are available on the market.In this thesis,Fe and Ni nanometer particles coated with carbon were prepared in a mixed atmosphere(2×10⁴pa,50%CH₄+20%H₂+30%Ar).The phase composition, morphology,particle size,surface characteristics,oxidation resistance and magnetic of nanometer particles were investigated with XRD,TEM,XPS,chemical analysis,oxygen analysis,TG analysis and VSM.The results indicate that the morphology of nanometer particles are similar spheric shape and form in a core-shell structure,and the core is Fe or Ni and the shell is carbon layer with 4nm or 3nm thickness.The nanometer particles mean particle sizes were 50nm and 20nm for Fe and Ni.With the temperature lower than 300℃, the oxidization resistance of samples of CH₄+H₂+Ar atmosphere is better than samples of H₂+Ar atmosphere,and the magnetization of samples of CH₄+H₂+Ar atmosphere is higher than samples of CH₄ atmosphere.The preparation of magnetic liquid is studied with Ni or Fe nanometer particles coated with carbon as magnetic particle,oleic acid as surfactant,miscible liquids of silicon oil and little silicone grease as base solution.The results show that viscosity increases with higher concentration of magnetic particle,and decreases with higher temperature.Saturation magnetization increases with higher concentration of magnetic particle,and there is no linear relationship observed.The viscosities of magnetic liquid are 2.6-6.0×10⁵ mPa.S at 25℃and 0.5-3.0×10⁵ mPa.S at 85℃.At room temperature,saturation magnetization of Fe magnetic liquid is 24.08-68.00Am²/kg and Ni magnetic liquid is 6.29-17.83 Am²/kg.A half year observation shows that silicon oil based magnetic liquid is stable in water and the mixture of petroleum and water.In H₂SO₄ or NaOH solution,silicon oil based magnetic liquid is stable when the concentrations of H₂SO₄ or NaOH are lower than 5%, but stability reduces quickly with higher concentration of H₂SO₄ or NaOH.