Study On Microwave Absorbers Based On Iron Nano-particles And Nanocomposite Particles

Monodispersed and polydispersed iron nano particles, and epoxy resin-iron composite particles have been synthesized. The structure of the particles was characterized by TEM> SEM\ IR, DSC, FTIR etc. The relationship between the particles structure and the microwave electromagnetical parameters have been studied detailedly in this thesis. The results showed in the following:1. Monodispersed particles may be synthesized by thermal decomposing iron pentacarbonyl in liquid phase containing lauryl-phosphate mono-ester as the surfactant. With increasing dosage of the surfactant, the grain size of the particles decreases, as a result, the permittivity decreases and the permeability increases. The minimal permittivity and the maximal permeability occur at the diameter of about 39 nm. Removing partial surfactant covering on nanoparticles reduce the permittivity of particles remarkably, but little effect on the permeability; Decreasing the aliphatic chain length of the surfactant can improve both permittivity and permeability of particles evidently.2. Polydispersed a -Fe nanoparticles have been obtained by using bi-amine terminated polyurethane flexible macromolecule as a surfactant, and on the basis of them, the epoxy-iron nanocomposite particles have been synthesized by in situ polymerization compositing technology. The real parts of both the permittivity and the permeability of the nanocomposite decrease firstly and then increse with increasing dose of surfactant. The composite particles have ideal comprehensive properties at the dosage of the sufactactant of 0.5 g, and its frequency dispersion exceeds that of traditional micrometer carbonyl iron powders. Thermal mass transfer is the key to mass production.3. The surface oxidation of the composite particles, breakage of the composite particles using ball milling or the addition of Span-80 when synthesized may reduce the permittivity of the composite particles, but the surface oxidation may also reduce the imaginary part of the permeability of the composite particles.4. Synergistic effect exists when the shell thickness of the micrometer iron-nano iron core-shell structure composite particles is about 120nm, at which the permeability greatly increases. The real part and the image part of the permeability at 2 GHz obviously greater by 25% than the corresponding values of the iron microparticles and iron nanoparticles.