Preparation And Characterization Of Micro & Nanometre Carbon-Iron Composite Materials

Due to the excellent physical and chemical properties, as well as the novel structure, the carbon micro-coils (CMC) have the promise of being used as an efficacious material for radar absorption. In this dissertation, the spring-like carbon fibers having distinct morphologies from the carbon micro-coils were successfully synthesized. Furthermore, the as-synthesized CMC were modified with nanometer ferrite and ferric grain. The electromagnetic properties of this new kind of composite material were investigated in detail.At first, the relevant researches about the helical carbon fibers were summarized. From the basic electromagnetic equations, electromagnetic parameters, and electromagnetic wave impedance matching theory to the spiral of carbon fiber, ferrite and iron-carbon composite materials, the contents of their research were reviewed in this paper, respectively.Secondly, the regular spring-like carbon fibers were fabricated by a catalytic pyrolysis method with acetylene as a carbon resource, Fe as a catalyst and thiophene as a promoter. The dependence of the products'structures on the preparation conditions, including the catalyst, additive thiophene, reaction temperature as well as gas composition and flow rate, etc. was explored. By optimizing experimental parameters, the uniform spring-like carbon fibers were obtained. It was demonstrated that the growth of the spring-like carbon fibers might be attributed to the process of gas-liquid-solid-solid, similar to the growth mechanism of CMC.The nano-sized ferrites and ferric particles with various morphologies were prepared by co-precipitation and liquid synthesis with polymer protection. The as-prepared nanoparticles were employed to fill and modify the CMCs through an optimized process. The electromagnetic properties of the synthesized iron-carbon composites were studied. It is indicated that the present composites own excellent electric as well as magnetic properties, and were expected to achieve better impedance matching.The gelatin-coated ferrous oxalate particles were fabricated as precursors by reverse micelles method. The precursors were subsequently reduced by hydrogen at a high temperature. As a result, the carbon-coated iron core-shell composite microspheres were obtained. The electromagnetic properties of the core-shell structure were characterized.It was found that the electromagnetic properties of the CMCs were strongly depended on the size of the CMC grain as well as th ratio of the CMC to matrices. These data could be utilized to design the coat for radar absorption in the further.