Synthesis of oxynitride composites during combustion of a ferrosilicon–natural mineral–aluminum mixture in nitrogen

Targeted synthesis of oxynitride composites is implemented by means of organizing coupled processes. Interaction of ferrosilicon with nitrogen in the combustion regime is considered as the main (inducing) process. The phase composition of the products of the coupled processes is determined by the chemical and phase compositions of the components added to ferrosilicon before performing self-propagating high-temperature synthesis. The influence of the basic products of the synthesis on the burning rate, fraction of nitrogen, phase composition, and morphology of synthesis products is considered. Chemical stages of ferrosilicon interaction with additives of natural minerals (zircon, ilmenite, and shungite) and aluminum in a nitrogen medium are demonstrated. The phase composition is determined by chemical transformations in the combustion wave. It is found that addition of aluminum leads to reduction or elimination of the Si$_2$N$_2$O phase in synthesis products with an increase in the aluminum fraction and obtaining composites based on the Si$_3$N$_4$ (SiAlON) solid solution. The microstructure of combustion products is presented by aggregates (5–10 $\mu$m) composed of small faceted crystals, shapeless structures, and crystal flakes. Oxynitride composites with an open porosity value of 51.0 $\div$ 68.8% are obtained.