Synthesis And Microwave Magnetic Properties Of Nanocomposite By Electroless Plating

Silica (SiO₂) nanoparticles have been widely used as nano-inorganic materials, and it has been subject to the scientific community and industry concerns. If the surface of SiO₂ nanoparticles has been modified, it will greatly expand its scope of application. Moreover, silica is a good low loss dielectric inorganic material, such a high resistivity dielectric material not only play the role of channel for the transmission of electromagnetic waves, but also plays the role of adjusting impedance matching between the atmosphere and the absorber.In this paper, the St(?)ber method was used to prepare the uniform nanoparticles firstly, then the alloy layers was to coated on the surface of nano-silica particles by electroless plating for constituting a core-shell structure of nano-composite magnetic materials and its microwave absorption property was studied.1. We use the modified St(?)ber method to prepare uniform and good dispersed silica nanoparticles. It was found that the silica nanoparticles prepared show the regular shape of standard spherical. The silver ammonia solution (Tollens reagent) is used to active the particle surface without catalytic activity. Under the more suitable conditions for electroless plating, we prepared series of Ni-P / SiO₂ samples with different plating times.2. Based on characteristic of morphology and in accordance with the law of the deposition of electroless plating, we have proposed electroless plating "adhesive-coated sphere into a corporation" process and "be separated from spherical reunion" process. The magnetic characterization was found that electroless plating Ni-P composite particles have good soft magnetic properties, electroless plating sample of 60 minutes has a good microwave absorbing properties. When the thickness of the specimen reached 2.9 mm, the samples have the greatest absorption of reflection, to -41.48 dB, and the best absorption frequency is 9.3 GHz.3. The colloidal palladium one-step activation method have been used to active the surface of silica particles without catalytic activity, and the activation of silica particles will enable the Ni-Fe-P ternary alloy to be deposited on the surface of silica powders. The electroless plating Ni-Fe-P composite particles have smaller saturation magnetization (less than 1 emu/g) and larger coercivity (greater than 60 Oe). In the entire frequency range and all matched thickness, the samples have smaller microwave absorption (no more than -5 dB).4. Silver ammonia solution is used for activation, and then the Ni-Co-P ternary alloy was successfully deposited on the surface of silica powders by electroless plating. It was found that in the initial stage of co-deposition of metal atoms, the increase of cobalt ion ratio benefit the increase of nickel ions co-deposition, when the two metal ions have the same ratio, the deposition rate reaches the maximum, and then the increase of the metal atom ratio is not conducive to the continued increase of nickel ions co-deposition. Opposite in the ratio of metal ions, regardless of the respective metal deposition rate, the total deposition rate is approximately constant, that is, the opposite ratio of the metal ions in the plating solution will lead to the same amount of metal deposition.5. In the surface of the Ni-Co-P / SiO₂ sample, the nickel element existed as Ni²⁺, cobalt element existed as Co²⁺, and phosphorus element existed mainly in the form of P³⁺ and P⁵⁺. There is no single substance existed regardless of metals or phosphorus.6. The saturation magnetization and remanence of the Ni-Co-P / SiO₂ samples increases when the cobalt atoms ratio increases from 25% to 75%. That is because cobalt has higher atomic magnetic moment and saturation magnetization than nickle.7. The maximum microwave loss of electroless Ni-Co-P / SiO₂ samples (Co 75 at.%) reaches -48.6 dB at 4.2 GHz with a thickness of 3.1 mm.