Chemical synthesis of metal nanoparticles dispersed in alumina

A procedure is described for obtaining nanocomposite powders consisting of metal nanoparticles homogeneously dispersed within alumina grains. We have prepared A1203/ x wt% Fe and Al203/x wt% Feo.sCr02 (x < 0.30)powders. Organometallic complexes containing AI 3÷ and Fe 3+ (and Cr 3+) were elaborated. The thermal decomposition of these precursors led to amorphous solid solutions of AI203, Fe203 (and Cr203), and further annealing led to crystalline solid solutions. The nanocomposite powders were then elaborated by selective reduction under hydrogen of these mixed-oxide solid solutions. Transmission electron microscopy observations have shown a bimodal size distribution of the metal particles (5 nm and 30 nm). Microstructural studies have shown that the location and size distribution of the metal particles are related not only to the homogeneity of the oxide solid solution, which is controlled by the solubility of Fe20s (and Cr203) in A1203, but also to their specific surface area, which is controlled by thermal treatments. Because of their nucleation in an homogeneous zone of the oxide solid solution, most of the metal particles are smaller than 5 nm and are intragranularly dispersed in the alumina matrix. The larger particles are nucleated in Fe203 overconcentration zones. Furthermore, the porosity of alumina allowed an exaggerated growth of some metal particles