Effect of Carbon Content on the Combustion and Chemical Transformation of Thermite Mixtures Based on Co3O4/Cr2O3/Nb2O5 with Al

The combustion of highly exothermic multicomponent mixtures of Co3O4/Cr2O3/Nb2O5/Al with additives of MoO3, WO3, 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 marked effect on the combustion, formation of chemical composition, and structure of combustion products. When the weight percentage of carbon in the initial mixture increases from 0 to 3.9%, the burning rate decreases by more than half and the rate of dispersion of combustion products and the mass 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 Co, Nb, Cr, W, Mo, C, and impurity aluminum, and the upper layer contains mainly Al2O3. With an increase in the carbon content above 4.0%, the separation of the metal and oxide phases ceases, and with a further increase, the flammability limit is reached. With an increase in the carbon content in the mixture from 0 to 3.9%, its concentration in the cast composite material reaches 5.4%, the Al content is about 4.0% and the content of Co, Nb, Cr, W, and Mo changes slightly. The combustion slag contains reducing metal oxide (Al2O3) and impurity Cr2O3 dissolved in it.