Effect of iron and boron ultrafine powders on combustion of aluminized solid propellants

The paper presents the results of measurement of the burning rate of aluminized composite solid propellants (CSPs) and parameters of sampled condensed combustion products including their particle size distribution, chemical and phase composition. Effect of ultra-fine iron and amorphous boron additives in CSP formulations based on AP, butadiene rubber and Alex (2 wt. %) on the combustion characteristics was studied. The sampled particles of condensed combustion products (CCPs) were classified as oxide particles (less than 55 µm) and agglomerate particles (up to 500 µm). The CCPs particles were subjected to morphological, particle size, chemical and phase analyses. It was found that partial replacement of Alex by 2 wt. % of iron in CSP leads to 1.3-1.4 fold increase in the burning rate in the pressure range of 2.2-7.5 MPa. At the same time the agglomeration of metal fuel is slightly increased: the mean diameter of agglomerate particles in CCPs is increased up to 1.2 fold and their content is increased up to 1.4 fold. The content and mean diameter of oxide particles in CCPs are reduced by 16 % and 13 %, respectively. Upon partial replacement of Alex by 2 wt. % of boron the burning rate is practically unchanged as compared with that for basic propellant with Alex. However the agglomeration is significantly enhanced, which is manifested at the increase in the agglomerate particles content in CCPs by 1.8-2.2 times, increase by 1.6-1.7 times in the agglomerates mean diameter and increase in the unburned metal fraction in agglomerates by 1.6-1.9 times. The content and the mean diameter of the oxide particles are reduced more significantly than in the case of iron introduction, namely, by 20-30 % and 30-40 %, respectively.