Effect of carbon content on the combustion and chemical conversion of thermite mixtures based on $\mathrm{Co}_3\mathrm{O}_4/\mathrm{Cr}_2\mathrm{O}_3/\mathrm{Nb}_2\mathrm{O}_5$ with $\mathrm{Al}$

The combustion of highly exothermic multicomponent mixtures of $\mathrm{Co}_3\mathrm{O}_4/\mathrm{Cr}_2\mathrm{O}_3/\mathrm{Nb}_2\mathrm{O}_5/\mathrm{Al}$ with additives of $\mathrm{Mo}\mathrm{O}_3$, $\mathrm{WO}_3$, and carbon (graphite) under overload up to $200$ g has been studied. It has been shown that the introduction of carbon into the initial mixture has a noticeable effect on the combustion, formation of chemical composition, and structure of combustion products. With an increase in the mass content of carbon in the initial mixture from $0$ to $3.9\%$ the burning rate decreases by more than half, and the rate of dispersion of combustion products and the weight loss increase markedly. Under the action of overload, the two-phase melt of combustion products is stratified into two layers, which crystallize upon cooling. The lower metal layer contains $\mathrm{Co}$, $\mathrm{Nb}$, $\mathrm{Cr}$, $\mathrm{W}$, $\mathrm{Mo}$, $\mathrm{С}$, and impurity aluminum, and the upper layer contains mainly $\mathrm{Al}_2\mathrm{O}_3$. With an increase in carbon content above $4.0\%$, the separation of the metal and oxide phases stops, and with a further increase, the flammability limit is reached. With an increase in carbon content in the mixture from $0$ to $3.9\%$, its concentration in the cast composite material reaches $5.4\%$, the $\mathrm{Al}$ content is about $4.0\%$ and the content of $\mathrm{Co}$, $\mathrm{Nb}$, $\mathrm{Cr}$, $\mathrm{W}$, and $\mathrm{Mo}$ changes slightly. The combustion slag contains reducer metal oxide $(\mathrm{Al}_2\mathrm{O}_3)$ and $\mathrm{Cr}_2\mathrm{O}_3$ impurity dissolved in it.