Towards Microwave Absorbing Metal-Oxide Nanocomposites: The Problem of Metal/Matrix Reaction

Thermostable microwave absorbing materials are of considerable interest for the applications with the tailored radar cross-section. Nanocomposites metal (Co, Fe)-dielectric (Al₂O₃, Al₂O₃2SiO₂, 3Al₂O₃2SiO₂) prepared by sol-gel route have been studied by electron microscopy and ⁵⁷Fe Mössbauer spectroscopy. The relationships between the micro/meso porosity, the composition and the state of the matrix precursor and the metal particle size are discussed with emphasis on the oxidation of nanoparticles. The size are discussed with emphasis on the oxidation of nanoparticles. Fe-based nanocomposites are obtained only using microporous host matrices. The interfacial reaction between iron nitrate solution precursor and host matrix promotes the formation of -(Fe_1-XAl₉)₂O₃ phase. The metal content is maximized by the use of highly concentrate iron solution and/or mixing with cobalt nitrate, in which case alloying particles are obtained.