Effect of iron powder on ignition and combustion characteristics of composite solid propellants

Effect of 2 wt. % iron nanopowder additive in the composition of composite solid propellants, containing 15.7 wt. % of aluminum nanopowder Alex, on the ignition and combustion characteristics of propellants and also on the composition of condensed combustion products was studied. It was found that partial replacement Alex by iron nanopowder in the composition of composite solid propellants leads to the decrease of the ignition delay time 1.3 - 1.9 times in the range of the heat flux density 55-220 W/cm$^2$ and to the increase of the reactive force of gasification products outflow from the burning surface of sample by 27 %, while the surface temperature of reaction layer is increased by 22 - 32 % at the moment of flame appearance. Law exponent of the burning rate is reduced from 0.51 to 0.43 and the burning rate is increased to 30 - 45 % in the range of nitrogen pressure in a constant pressure bomb 2.0 - 7.5 MPa. The analysis of the selected combustion products has shown that an additive of iron nanopowder decreases the relative mass of k-phase from 0.25 to 0.19. At the same time the content of aluminum oxide $\alpha$-Al$_2$O$_3$, aluminum nitride AlN and carbon nitride increases and the content of monoclinic aluminum oxide $\theta$-Al$_2$O$_3$ decreases due to the possible increase of the temperature gradient and the rate of chemical reactions in the gas phase combustion zone of composite solid propellant.