Chemical synthesis of metal nanoparticles dispersed in alumina

Abstract

A procedure is described for obtaining nanocomposite powders consisting of metal nanoparticles homogeneously dispersed within alumina grains. We have prepared Al 2 O 3/ x wt%Fe and A 2O 3/x wt% Fe 0.8Cr 0.2 (x ≤ 0.30) powders. Organometallic complexes containing Al 3+ and Fe 3+ (and Cr 3+) were elaboated. The thermal decomposition of these precursors led to amorphous solid solutions of Al 2O 3, Fe 2O 3 (and Cr 2O 3 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 Fe 2O 3 (and Cr 2O 3) in Al 2O 3, but also to their specific surface area, which is controlled by thermal treatments. Because of their nucleation in an homogenous 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 Fe 2O 3 overconcentration zones. Furthermore, the porosity of alumina allowed an exaggerated growth of some metal particles.