Combustion synthesis mechanism of the Ni(NO3)2 + hexamethylenetetramine solutions to prepare nickel nanomaterials

• Published in: Combustion and flame 2023-11, Vol.257, p.113049, Article 113049
• Main Authors: Zakaryan, Marieta K., Amirkhanyan, Narine H., Nazaretyan, Khachik T., Kharatyan, Suren L., Manukyan, Khachatur V.
• Format: Article
• Language: English
• Subjects: Combustion synthesis; Low–temperature sintering; Nickel nanomaterials; Reaction mechanism
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2023.113049

This work reports the combustion synthesis mechanism in a system with hexamethylenetetramine (C6H12N4) as the fuel and nickel nitrate (Ni(NO3)2) as the oxidizer. Detailed investigations using combustion diagnostic methods, thermal analysis, and mass spectroscopy measurements allow us to propose that the process includes the multistage decomposition of the oxidizer and sublimation of the fuel. The latter decomposes at the gas phase and releases nitrogen (N2), hydrazine (N2H4), and methane (CH4). The nitrogen oxides (NO, NO2, N2O) emitted at the decomposition of Ni(NO3)2·2Ni(OH)2·4H2O intermediate, react with CH4 and N2H4. These highly exothermic reactions determine the maximum temperature of combustion. Comparative kinetic consideration allows us to attribute the Ni(NO3)2·2Ni(OH)2·4H2O decomposition producing nitrogen oxides and nickel oxide (NiO) as the rate-limiting stage of the process. Excessive amounts of N2H4 and CH4 in the fuel-rich system reduce NiO to nanoscale Ni. The synthesized Ni readily consolidates into samples with relative densities above 90%, even at 773 K during fast processing.