| Magnetic nanomaterials have different special nature from converti-onal magnetic materials in Physical and Chemical area, due to the uniquemagnetic.But magnetic nanoparticles have the problems of lack offunctional groups and tendency of agglomeration, and the magneticcomponent alone can not satisfy the wider use, nanocomposite materialscontaining a magnetic core and another shell have attracted much interestfrom material science. Silver become a favored coating material becauseof its simple synthetic procedure, good chemical stability and nontoxicity.The magnetic nanocomposites with silver coating will use in electro-magnetic shielding area and have better shielding effectiveness in thefield of broadband. This article used magnetic Fe304 particle as core forthe first time and the silver-coated core-shell shielding particles wereprepared by liquid phase chemical deposition. The preparation ofmagnetic Fe304 particles and the properties of core- shell compositeswere systemically studied.The conclusions are enumerated as follow:(1) Using SDS and PVP as surface active agent, the block ferreroxalates are sythesised at 100℃. The block Fe304 particles are got by thedecompos-ition of ferrer oxalate at above 500C. The static magneticproperties of Fe3O4 particles are measured with vibrating samplemagnetometer in the different decomposition conditions. With thetemperature increasing, the saturation magnetization of productsincreased. When reached 500C, it is the maximum. Effection ofdecomposition time is not great, 3h is better. The magnetic propertiesunder one step of increasing temperature are better than that under twosteps.(2) Fe3O4 nanoparticles are synthesized by sol-gel methord.Different size and morphology of Fe3O4 were prepared under FeSO4, FeSO4·(NH4)2 SO4·6H2O and FeCL2 resolution, Correspondly, the size is80nm of Polyhedron, 100-200rim of sphere and 40nm of sphere. With thereaction temperature increased, the size of particles increases,dispersibility is worse. When the reaction temperature reaches to 90℃,the morphology of the products is polyhedron and dispersibility is better.The saturation magnetization values are large under three conditions, thecoercive force shows dependency on size and morphology.Using NaBH as reductant, the silver-coated nanocomposites areprepared by liquid phase chemical deposition, the size of Ag particles issmaller, formed a strawberry-shaped core-shell structure.(3) Fe3O4/Ag core-shell nanoparticles are prepared by liquid phasechemical deposition, with teytamethylammonium hydroxide solution,mercapto propyl trimethoxy silane and Na2S as additive. The result withMPTS is best. The size distributions of core-shell Fe3O4/Ag compositesaveraged 40—50nm, the conductivity of the compound particles is1320.48S/cm. The effection of pH value is important, with the pH valueincreased, the saturation magnetization of nanocomposites graduallydecrease, and the conductivity gradually increase. When pH value is13.5±1,the result is better.
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