Solution Combustion Synthesis of Nano-Crystalline Metallic Materials: Mechanistic Studies

The mechanism of structural transformation during combustion of nickel nitrate (oxidizer)-glycine (fuel) system is investigated by using different in situ techniques, including time-resolved X-ray diffraction (TRXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) with dynamic mass spectrometry (MS), and high-speed infrared thermal imaging. It is shown that for initial compositions with a relatively large fuel-to-oxidizer ratio (phi), pure Ni phase forms directly in the combustion front. For fuel-lean conditions, only NiO phase can be detected. Analysis of the obtained data, including transmission and scanning electron microscopy (TEM-SEM) studies of the quenched reaction fronts, allows us to suggest the intrinsic mechanism of pure metal formation in the investigated system. It is shown that the combustion front propagates because of the reaction between N2O and NH3, which are the products of decomposition of the oxidizer and fuel. The excess of NH3 gas produced in fuel-rich conditions rapidly (<0.2 s) reduces nickel oxide to pure metal in the reaction front.