Effect of addition of potassium carbonate to aluminum powder on the grain size of Al$_2$O$_3$ nanoparticles formed in the laminar dusty flame

Results of studying the effect of K$_2$CO$_3$ additives on the grain size of the products of combustion of a gas suspension of Al particles (with the mean particle diameter of 4.8 mm) in a laminar diffusion flame are reported. An extreme character of the dependence of the mean size of Al$_2$O$_3$ particles on the additive concentration is experimentally observed. For the concentration of the K$_2$CO$_3$ additive equal to 0.5%, the mean diameter of Al$_2$O$_3$ particles is 30 nm; for the additive concentration of 5%, the mean particle size increases to 67 nm. It is demonstrated that the change in the mean size of Al$_2$O$_3$ particles as a function of the concentration of the readily ionized additive is caused by interaction of the dusty and ionic subsystems of the plasma of the combustion products in the reaction zone in the flame. At a high concentration of ions (above 10$^{20}$ m$^{-3}$), this interaction increases the rate of coagulation of Al$_2$O$_3$ particles.