Thermal analysis of the products of SCS of zinc nitrate with glycine and citric acid

Highlights: • Carbon and fragments of citric acid pyrolysis are formed in the process of SCS. • Oxidation temperature of carbonaceous fragments is 350–500 °C. • Carbonaceous structure of mixed sp²–sp³ nature are detected in the samples upon annealing at 650 °C. The composition of powders produced in reactions of Solution Combustion Synthesis (SCS) of zinc nitrate with glycine and a mixture of glycine and citric acid has been studied. The precursors formed on completion of solution combustion reactions were established to contain ZnO and up to 7 wt% of carbonaceous fragments due to incomplete oxidation of fuel. The latter are mixtures of residual carbon (0.2−3 wt%) and the fragments of citric acid decomposition, bound carbon, (0.6–4.4 wt%), which are strongly disordered carbon structures in nature, including amorphous ones. The performed thermal analysis of precursors and modeling allow us to suppose that the process of additional oxidation takes place in two stages – at 240−280 °C (oxidation of organic fragments) and 410−424 °C (oxidation of residual carbon) and is incomplete in character. It was shown that the complete removal of the carbonaceous fragments of organic fuel needs the temperatures close or over 900 °C. The best conductivity of ZnO were 1.13·10⁻⁷ and 9.19·10⁻⁸ S/cm after SCS and annealing 650 °C, respectively.