Synthesis And Characterization On Radar Absorbing Matererials Of Conducting Polyaniline Composites With Barium Ferrite Nano-particles

The microwave absorbing materials in future are characterized by thin thickness, light mass, wide range, strong absorption, and are required to endure high temperature, oceanic weather, nuclear radiation and so on. Polyaniline (PANI) and its derivatives, especially doped conducting polymer, might become a new kind of microwave absorbing materials owing to its easy preparation, good environmental stability and high microwave absorption. M-type barium ferrite powders could be used as microwave absorbers for X-band frequencies because of its high magnetic anistropic. The conducting polyaniline/barium ferrite nanocomposites possess both dielectric losses and magnetic losses, so they have good application prospect in radar absorbing materials.Conducting polyaniline (PANI) and poly-O-methylaniline (POT) have been synthesized by chemical oxidation method. The structures and properties of PANI and POT have been studied by TEM, FTIR, UV-Vis, XRD and so on. The results show that the doped polyaniline (PANI-HC1) has club shape, while the doped poly-Ormethylaniline (POT-HC1) has grain shape. In comparison with their corresponding undoping polymers, both PANI and POT doped by HCl render their higher conductivity. According to the contrasts between the structure of PANI and that of POT, the conclusion could be made that steric hinderance effect of methyl groups in the poly-O-methylaniline is more prominent than induction effect and hyperconjugation.Ti-Mn Substituted barium ferrite nanoparticles have been prepared by Sol-Gel method and coprecipitation-melted salt method respectively. The spectra analysis of TEM and XRD shows that the crystallite size of BaFe₈(Ti_0.5Mn_0.5)₄O₁₉ prepared by Sol-Gel method is more uniform than that by coprecipitation-melted method. With the increase of sintered temperature, the barium ferrites prepared by coprecipitation-melted salt method come from imperfect crystal to perfect crystal, while the barium ferrites prepared by Sol-Gel method come from soft magnetic phases to permanent magnetic phases, and there are two phases in 800℃.PANI/BaFe₈(Ti_0.5Mn_0.5)₄O₁₉ nanocomposites and POT/BaFe₈(Ti_0.5Mn_0.5)₄O₁₉ nanocomposites with "cake-pignut" structure have been prepared by in situcomposite technique in the presence of BaFeg(Tio.5Mno 5)4019 nanoparticles. XRD, TEM. VSM, FTIR, UV-Vis are used to characterize the composites' structure, electrical property and ferromagnetic property. The results show that the conducting polymers can reduce the agglomeration of BaFe8(Tio.5Mno.s)40i9 particles to some extent. Two nanocomposites possess conductivity and magnetization. With the increase of polymer contents, the conductivities of the composites are increased, but the magnetic properties are reduced. There are a - n chemical bonds between PANI and BaFesCTio.sMno.s^Oig in PANI/ BaFe8(Tio5Mno.5)40i9 nanocomposites, while there are not chemical bonds between POT and BaFe8(Tio.5Mno.5)40i9 in POT/BaFegCTio.sMno.s^Oig nanocomposites because of steric hinderance effect of methyl groups in the poly-O-methylanilineRadar microwave absorbing properties of PANI/BaFeg(Tio.5Mno.5)40i9 nanocomposites and polyaniline are characterized by the vector network analyzer. The results show that the conducting polyaniline doped by HCl has high electric losses, but low magnetic losses. Therefore, it is not ideal microwave absorbing material. PANI/BaFesCTio.sMno.5)4019 nanocomposites show good microwave absorption in the range of 2—18 GHz. It is founded that a reflectivity of-29.5 dB and 5 GHz of 10 dB bandwidth can be achieved by the composite materials of 2mm in thickness. It means the novel materials will be used widely as radar absorbing materials.The conducting polymer/barium ferrite nanocomposites have application prospect in radar absorbing material, conducting material and optoelectronic display because the composite materials have such properties as conductivity, magnetism and nanostructrue effect. The research of these nanocomposites still is placed in the initiative stage, so this work should be carried out deeply.