Synthesis of nanostructured materials in supercritical ammonia: nitrides, metals and oxides

In this study, the synthesis of nanostructured particles of nitrides (Cr2N, Co2N, Fe4N, Cu3N, Ni3N), metal (Cu) and oxides (Al2O3, TiO2, Ga2O3) 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 degreesC 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.