Preparation And Radar/Infrared Stealth Characteristics Of Mesoporous Carbon-Metal Nanocomposites

This dissertation presents ordered mesoporous carbon/metal or metal oxide nanocomposites with the comprehensive use of inserting air cavity and sub-division methods. These nanocomposites can efficiently attenuate electromagnetic wave taking the advantages of robust channel structure and proper impedance matching. They also exhibit low infrared emissivities at 8¹4μm through the component adjustment, which would provide the theory and technology reference for the development of lightweight and highly efficient stealth materials. The main contents are as follows:On the basis of sub-division method, we prepare mesoporous carbon and ferrite nanocomposites to realize meso-scopic impedance matching. Glucose-based carbon coated ferrite was prepared under solvothermal conditions. After heat treatment at 500℃, the composites are composed of mesoporous carbon as shell and ferrite as core. They are tuned into Fe/C core-shell nanoparticles when heat treatment at 1000℃. After carbon coating, the infrared emissivity at 8¹4μm of the ferrite particles can be lowered to 0.5, and the absorption of electromagnetic wave at 0.5¹8 GHz is enhanced. The effective absorption bandwidth can exceed 4 GHz. At the elevated temperature of 1000℃, it presents the minimum reflectivity below -20 dB with the matching thickness of 2⁹ mm, with the absorption peaks focusing on the low frequency bands.We propose the idea of inserting air cavity and attempt to prepare carbon/metal oxide nanocomposites using triconstituent co-assembly method. On the basis of template direction of surfactant F127, C-Fe₂O₃, C-Al₂O₃, and C-TiO₂ nanocomposites were prepared using ferric citrate, aluminum isopropoxide, and titanium isobutoxide as metal precursors, respectively. The metal oxides sustain with carbon in the framework of these nanocomposites with a typical two-dimensional hexagonal mesoporous structure. The results show that the infrared emissivity can be controlled within 0.4⁰.55 after the introduction of metal oxide particles, which is much lower than that of pure mesoporous carbon. Additionally, the absorption peak is also widened. The effective absorption bandwidth can reach 6.7 GHz and the minimum reflectivity is as low as -52.4 dB.In order to further develop the efficiency of the large saturation magnetization of magnetic metal based on the idea of inserting air cavity, ordered mesoporous carbon-silica nanocomposites with magnetic metal constituents were prepared by a facile solvent-evaporation-induced self-assembly approach. Magneticα-Fe nanocrystallines are in situ grown in the nanocomposites through a high temperature heat treatment. This strategy would enhance the magnetic loss. CS-Fe-700 exhibits multi-band absorption characteristics, its effective absorption bandwidth is found to exceed 5.0 GHz. With the addition of the second metal such as Co, Ni, Cu, etc., the frequency of reflection loss could cover 2.8¹8 GHz by changing the matching thickness. In addition, the infrared emissivity could be reduced from 0.677 of pure C-SiO2 to 0.498.Furthermore, magnetic metal embedded into ordered mesoporous carbon can also be realized through impregnation-loading method. Ordered mesoporous carbon powders were used to impregnate tetracarboxy phthalocyanine iron solution for loading. After heat treatment of 700℃, the frequency of reflection loss could cover 3.1¹8 GHz by changing the matching thickness.Impedance matching and fast loss of electromagnetic energy are the main causes to the super microwave absorption property of ordered mesoporous nanocomposites. Ordered mesoporous carbon materials with the introduction of magnetic constituents are easy to realize the impedance matching between the materials and free space. Furthermore, the nanocomposites possess robust channel structure, high surface area, and unique interface effect. It could take the advantages of high loss with magnetic constituents as well as the conductance loss and dielectric relaxation with mesoporous carbon. Electromagnetic wave can be dissipated through the directional conduct of the mesoporus structure and the electromagnetic energy would be fully absorbed. It can also obtain the lower infrared emissivity, meeting the needs of lightweight and highly efficient stealth materials.