| Radar absorbing material is a key link of radar stealth technology. For microwave-absorbing material, the implementation of the absorption of electromagnetic wave depends on the adjustment of electromagnetic parameters. However, electromagnetic parameters of the microwave-absorbing material have something to do with some factors such as their particle size, morphology, structure, and composition. Therefore, it is very meaningful to explore the preparation methods of microwave-absorbing materials with special morphology, structure and composition to improve materials’ microwave-absorbing properties. For this purpose, two aspects of work have been done in this paper, and specific research contents and main conclusions are summarized as follows:(1) Shape-controlled Fe3O4 nanocrystals were synthesized by a surfactant-assisted or template-free thermal decomposition method at a lower temperature with Fe(CO)5 as basic raw material. The effects of the dosage of Fe(CO)5, the dosage of dodecyl dimethyl betaine, the reaction temperature, the reaction time and the kinds of solvent on structures and morphologies of as-synthesized products were explored. In addition, the magnetic performance and microwave-absorbing performance of products were also studied. The experimental results indicated that three-dimentional flower-like Fe3O4 particles could be obtained in the mixed reaction system composed of 1-methyl-2-pyrrolidone and dodecyl dimethyl betaine, and flower-like Fe3O4 particles couldn’t be prepared when the reaction temperature was too high or too low. Besides, the possible formation mechanism of flower-like Fe3O4 particles was discussed. Through the investigation of the possible formation mechanism, we believed that water played a certain role in shape evolution of the products, and experiments were also done to confirm this viewpoint. The experimental results showed that when the mixed reaction system were formed by 1-methyl-2-pyrrolidone and water, the content of water was found to have an important impact on the morphology of products:with the change of the dosage of water, uniform flower-like Fe3O4 and timbo-like nano/micrometer Fe3O4 particles were prepared. Therefore, one-step syntnesis of uniform Fe3O4 without the aid of surfactant was realized. In addition, when the mass ratio of water to 1-methyl-2-pyrrolidone was 1:10.4, rhombic dodecahedral Fe3O4 nanoparticles could be acquired by adding dodecyl dimethyl betaine. As can be known from the results of magnetic performance tests, the as-prepared products belong to ferromagnetic material, and saturation magnetization, remanent magnetization and coercivity of product vary with changes of their morphologies and sizes. In terms of results of microwave-absorbing performance tests, flower-like Fe3O4 particles and rhombic dodecahedral Fe3O4 nanoparticles exhibit different absorbing properties:when the layer thickness ranges from 1 mm to 4 mm, rhombic dodecahedral Fe3O4 nanoparticles exhibit a better microwave-absorbing property, a maximum reflection loss of 14.84 dB at 8.48 GHz is observed with a bandwidth of 3.44 GHz above 10 dB loss when layer thickness is 3 mm; when the layer thickness is 5 mm, flower-like Fe3O4 nanoparticles exhibit a better microwave-absorbing property, the maximum reflection loss of flower-like Fe3O4 is 19.04 dB at 16.72 GHz with a bandwidth of 3.28 GHz above 10 dB loss, however, the maximum reflection loss of rhombic dodecahedral Fe3O4 nanoparticles is 18.98 dB at 3.2 GHz with a bandwidth of 2.48 GHz above 10 dB loss.(2) At first, α-FeOOH nanorods were prepared with ferric nitrate and potassium hydroxide as basic raw materials. Influences of reactant concentration, reaction time, dosage of chelating agent, types and dosages of surfactants and other reaction conditions on the morphologies and phase compositions of the products were investigated. Then α-FeOOH/PANI nanocomposite was prepared by chemical polymerization method, and its microwave-absorbing property was also investigated. The results of the experiment showed that the addition of surfactants and chelating agent could influence the products. The addition of sodium dodecyl sulfate, dodecyl dimethyl betaine and cetyltrimethyl ammonium bromide has an obvious effect on the size of product. The addition of Na2EDTA can obviously influence the morphology, size and crystallinity of the product. According to the result of microwave-absorbing performance test, α-FeOOH/PANI nanocomposite can have the optimal microwave absorption performance when the layer thickness is 2 mm, a maximum reflection loss of 16.98 dB at 11.6 GHz is observed with the frequency ranging from 10.24 GHz to 13.52 GHz above 10 dB loss. |
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