Effect of $\mathrm{SiO}_2$ content and mechanical activation on $\mathrm{Ni}$–$\mathrm{Al}$–$\mathrm{SiO}_2$ combustion

This study describes the effect of preliminary mechanical activation and $\mathrm{SiO}_2$ quartz content on combustion rate, maximum combustion temperature, sample elongation during combustion, compressibility of mixtures, composite particle size, phase composition, and the structural features of combustion products in a $\mathrm{Ni}$–$\mathrm{Al}$–$\mathrm{SiO}_2$ system. In $\mathrm{Ni}+\mathrm{Al}+\mathrm{SiO}_2$ initial mixtures, not subjected to mechanical activation, it is not possible to initiate combustion at room temperature if the mass content of $\mathrm{SiO}_2$ quartz exceeds $10\%$. Preliminary mechanical activation of the $\mathrm{Ni}+\mathrm{Al}+x\mathrm{SiO}_2$ reaction mixture expands the limit of quartz content in the mixture, at which it is possible to realize the combustion of pressed samples at room temperature, up to $40\%$. The burning rate and sample elongation during combustion increase significantly after the reaction mixtures are mechanically treated, and the relative density of the samples, obtained at a fixed pressing pressure, decreases. The increasing quartz content in the $\mathrm{Ni}+\mathrm{Al}+x\mathrm{SiO}_2$ reduces the combustion rate, the maximum combustion temperature, and the sample elongation during the combustion of both the initial and mechanically activated mixtures. Moreover, as the quartz content increases, so does the sample density reached at a fixed pressing pressure in the case of initial mixtures, while the density in the case of mechanically activated mixtures is virtually not affected. The increasing quartz content also reduces the composite particle size after mechanical activation and increases the number of phases formed in the reaction products. An explanation for most of the observed relationships is proposed.