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

Abstract

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 (φ), 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 N 2 O and NH 3 , which are the products of decomposition of the oxidizer and fuel. The excess of NH 3 gas produced in fuel-rich conditions rapidly (<0.2 s) reduces nickel oxide to pure metal in the reaction front.

Effect of the Fuels Glycine, Urea and Citric Acid on Synthesis of the Ceramic Pigment ZnCr2O4 by Solution Combustion

“…Figure 1 shows the thermal analysis of differential scanning calorimetry (DSC) and thermogravimetric analysis for the samples obtained after combustion reaction between fuels and the metal nitrates. The three graphics present a similar form where an exothermic band is identified with a peak about 100 °C, which is probably due to loss of decomposition of organic matter by the sample, also another exothermic band is observed between 200 °C and 900 °C, which are ascribed to organic matter that was not removed during combustion, in the literature is reported the decomposition of glycine in a nitrogen atmosphere 18 , which started at 250 °C with the production of NH 3 , CO 2 , H 2 O, a dipeptide and 2,5-piperazinedione compounds, later at 450 °C dipeptide and 2,5-piperazinedione are decomposed in HNCO, HCN, CO 2 , NH 3 , and H 2 O. The results show that the products of synthesis are different, because there is a mass loss between 25 °C and 900 °C which are of 20%, 8%, and 10% for glycine, urea, and citric acid, respectively.…”

Conventional versus microwave combustion synthesis of CoFe2O4 nanoparticles

“…oxygen surrounding the precursor at the combustion stage, resulting in the lack of oxygen for metal (Fe/Co) oxidation [18,19,23]. The CoFe phase was observed for the first time using microwave-induced combustion of metal nitrates-citric acid gels.…”

“…The exothermic reaction starts in a self-sustaining regime after being heated up to the ignition temperature. The chemical energy released from the exothermic reaction between the metal nitrates and fuel can rapidly heat the system to a high temperature ([1200°C) without any external heat sources [18]. Combustion-synthesized powders are generally more homogeneous, have fewer impurities, and have higher surface areas without hard agglomerates compared with powders prepared by the conventional solid-state methods [19].…”

Combustion/micropyretic synthesis of atomically thin two-dimensional materials for energy applications

“…Another modification of the SHS process, termed a solid state metathesis (SSM), uses highly exothermic reactions between a metal pnictide, chalcogenide, silicide or boride with a metal halide and combustion reaction takes place primarily between gasified precursors [8]. Solution combustion synthesis (SCS) was developed to prepare complex nanostructured oxides, as well as metals, by self-sustained reactions in aqueous solutions of water-soluble metal nitrates and fuels (amines, acids and aminoacids) [9,10 ]. Finally, flame synthesis (FS) has a long history and has developed separately from other combustionbased techniques.…”