Synthèse, Caractérisation et Étude des Propriétés Magnétiques et Diélectriques de Nanocomposites Polyaniline/Hexaferrite pour l'Absorption des Micro-ondes

This thesis deals with the formulation of Polyaniline/hexaferrite nanocomposite for absorbing electromagnetic waves. The main idea is the process of composite materials based on polymers intrinsic conductors such as Polyaniline that we doped with different types of acids (HCl, CSA, NSA, and ... TSA) and barium hexaferrite with magnetoplumbite structure with or without substitution according to desired stoichiometries. In the barium hexaferrite, the substitution of Fe 3+ is made by Al3+, Bi3+, Cr3+ and Mn3+ ions. The barium hexaferrite and its substitutions by different ions mentioned above were synthesized dynamic hydrothermal method by varying various parameters during the synthesis (pH, temperature, time, ratio [OH-]/[NO3-] ...). The elaboration of polyaniline/hexaferrite composite (pure or substituted) was carried out by oxidative polymerization using various synthesis techniques: Aqueous-Based Polymerization with or without agitation (taking into account the nature of the acid used) (ABP) and Solid-Based Polymerization (SBP). The optimization of these various synthesis techniques after physicochemical (XRD, FTIR, TGA, SEM, EDX), dielectric (ε', ε'', σdc) and magnetic (Mr, Ms, Hc, Tc, μ', μ'') characterizations of the samples showed that the solid route is the easiest method, economical and environmentally friendly It is also suitable for the production of composite Pani/BaFe12O19 with good structural, physical and magnetic properties. The study of the substitution of Fe3+ in the BaFe12O19 by Al3+, Bi3+, Cr3+ and Mn3+ showed a strong dependence of the structural and magnetic properties with the distribution of these ions in the hexagonal crystal lattice. In fact, A3+, Cr3+ and Mn3+ ions tend to occupy the tetrahedral sites, while the Bi3+ favored the octahedral sites. An increase in Hc associated with the small crystallite size observed for particles substituted with Al and Cr and the enhancement magnetocristalline anisotropy (strong higher order term) for Bi and Mn due to their high ionic radius. The incorporation of the substituted hexaferrite in the Polyaniline to obtain Pani/BaMeFe11O19 composite, where Me = Al, Bi, Cr and Mn, reveals a variation in electromagnetic properties in the frequency range from 1 to 18 GHz. In fact, these variations are due to the formation of dipoles between the substituting ion and surrounding O2- cations in the ferrite which are responsible for the ferromagnetic resonance, the magnetocrystalline anisotropy and the exchange interaction with the polymer. The composite Pani/BaFe12O19 shows absorption bands at the X-band that shift to the Ku-band with the substitution of iron, confirming the potential of these materials for microwave applications