چكيده به لاتين
In this thesis, due to the importance of the electromagnetic interferences, microwave absorbing materials with magnetic and dielectric properties having microwave absorption bandwidth more than 2 GHz (10dB>), as well as maximum absorption of more than 20 dB, were prepared considering the effective parameters on the microwave absorption performance. Accordingly, magnetic nanoparticles such as Sr0.5Ba0.5Fe11Al0.5Cr0.5O19, La0.8Sr0.2FeO3, SrAl1.3Fe10.7O19, and Ba0.2Sr0.2La0.6MnO3 with various magnetic properties were prepared using a range of solution techniques, including Pechini method builds on the principles of sol–gel chemistry involving small molecule chelating ligands, hydrothermal, and solvothermal methods. Moreover, the influence of small molecule chelating ligands such as polymethylmethacrylate, citric acid and glucose were investigated on the microwave absorption properties. Besides, uniform coverage by polyaniline and multiwall carbon nanotube using several matrices such as silicone rubber, polyurethane, paraffin, and polyvinyl chloride on the microwave attenuation were compared and examined. A novel polymerization procedure of aniline in aqueous medium in the presence of dodecylbenzene sulfonic acid (DBSA) as a dopant is also reported. This polymerization yields stable dispersions of the emeraldine salt, enhances the interfaces and polarizations. The molar ratio of the dodecylbenzene sulfonic acid was adjusted to enhance its electrical conductivity. Finally, multiwalled carbon nanotubes were functionalized using a modified acid treatment method and then were uniformly dispersed within the medium using polyethylene glycol or polymethyl metha acrylate to reinforce the polarizations. The nanostructures were characterized using Fourier transform infrared (FT-IR), elemental mapping analysis, field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), four-point probe conductometer (FPPC), and X-ray powder diffraction (XRD) analysis. The optical performance of the prepared nanostructures was evaluated by diffuse reflection spectroscopy (DRS) method. The four-point probe conductometer result showed significant electrical conductivity (449.51 S/cm) for the modified polyaniline. Finally, microwave absorption results were investigated by vector network analyzer (VNA) instrument showing i. e. maximum reflection loss of polyurethane foam/polyaniline 50Wt. % was 84.90 dB at 10.22 GHz frequency with 5.1 GHz bandwidth more than 10 dB and thickness of 3.5 mm also absorbed 69.20 dB at 13.86 GHz with 2.5 mm in thickness while absorbed 9.21 GHz more than 10 dB along the x and ku-band.
