Elaboration and thermal stability of (alumina, aluminosilicate/iron, cobalt, nickel) magnetic nanocomposites prepared through a sol-gel route

Abstract

Optically clear monolithic (OCM) gels of alumina and aluminosilicates can be prepared by hydrolysis-polycondensation of alkoxides. Subsequent heating induces transformation firstly into OCM mesoporous glasses and then into dense translucent or optically clear ceramics, the densification occurring at low temperature. Immersion of alumina or aluminosilicate gels and glasses in aqueous solutions containing transition metal (cobalt, iron, nickel) ions leads to diffusion of these ions into the water within the pores of the monoliths. After heat treatment under hydrogen, metallic nanoprecipitates are obtained. The size of the precipitates, as studied by transmission electron microscopy, ranges from 5 to 70 nm depending on the host matrix. The thermal stability in air of these materials was studied by differential thermal and analysis X-ray diffraction. The oxidation of porous composites occurs above 600 °C in air. Magnetic parameters such as coercitive field, magnetization, etc. were also measured.