No abstract

In this study, the synthesis of nanostructured particles of nitrides (Cr 2 N, Co 2 N, Fe 4 N, Cu 3 N, Ni 3 N), metal (Cu) and oxides (Al 2 O 3 , TiO 2 , Ga 2 O 3 ) by using supercritical ammonia in the reaction medium is described. The elaboration process is based on the thermal decomposition of metal precursors in a supercritical ammonia-methanol mixture at a range of temperatures between 170 and 290 °C at about 16 MPa. Nitrides are obtained at relatively low temperatures in comparison with classical processes. It is shown that the chemical composition of the produced materials can be controlled by the adjustment of process operating conditions (pressure, temperature, metal precursor concentration and residence time in the elaboration reactor) and by the knowledge of the Gibbs free energy of oxide formation of the studied metal.

Supercritical fluids exhibit a range of unusual properties that can be exploited for the development of new reactions for material synthesis. These reactions are different from those performed in classical solid-state chemistry. Supercritical fluids are interesting as reaction media for the synthesis of nanostructured materials because fluid properties such as density, viscosity, diffusivity and solubility of reagents can be continuously tuned from gas to liquid with small variations in pressure and temperature. Moreover, supercritical fluid processing offers the possibility of using solvents with low toxicity that result in nanostructured materials free of solvent contamination. The process developed at ICMCB obtains nanostructured materials by chemically transforming a metal precursor inside a supercritical fluid. The synthesis of nanostructured materials such as metals, oxides or nitrides is possible at lower temperatures than the classic solid-state chemistry route. Based on experimental results and simulations, the nanostructured material nature, size and morphology can be continuously adjusted as a function of the operating condutions. Our process provides a great contribution in the development of self-assembled nanostructured materials by controlling the chemical composition, size, morphology and the surface properties of nanobricks.