ELABORATION AND THERMAL-STABILITY OF (ALUMINA, ALUMINOSILICATE IRON, COBALT, NICKEL) MAGNETIC NANOCOMPOSITES PREPARED THROUGH A SOL-GEL ROUTE

Optically clear monolithic (OCM) gels of alumina and aluminosilicates can be prepared by hydrolysis-polycondensation of alkoxides. Subsequen t heating induces transformation firstly into OCM mesoporous glasses a nd then into dense translucent or optically clear ceramics, the densif ication occurring at low temperature. Immersion of alumina or aluminos ilicate gels and glasses in aqueous solutions containing transition me tal (cobalt, iron, nickel) ions leads to diffusion of these ions into the water within the pores of the monoliths. After heat treatment unde r hydrogen, metallic nanoprecipitates are obtained. The size of the pr ecipitates, as studied by transmission electron microscopy, ranges fro m 5 to 70 nm depending on the host matrix. The thermal stability in ai r of these materials was studied by differential thermal and analysis X-ray diffraction. The oxidation of porous composites occurs above 600 -degrees-C in air. Magnetic parameters such as coercitive field, magne tization, etc. were also measured.