Role of Oxides of Iron on the Combustion of Composite Solid Propellants: A Review

Abstract

The effects of iron oxides (α-Fe2O3, γ-Fe2O3, Fe3O4 in the different size ranges from micron to nano) on the combustion of composite solid propellants, also known as hydroxyl terminated polybutadiene/aluminium/ammonium perchlorate (HTPB/Al/AP) systems, are thoroughly reviewed in this work. The effect of the oxides of iron in (i) condensed phase; (ii) sub-surface and surface; (iii) premix flame (gas phase); and (iv) final flame (gas phase) in deflagration zone are also critically reviewed. The effect of catalyst on the lower pressure limit (LPL), upper pressure limit (UPL) and ignition delay is also studied as a part of the combustion phases. It is understood that unlike during the combustion of pure ammonium perchlorate, the role of iron oxides starts its influence on binder system degradation, binder-ammonium perchlorate reactions at surface and HClO4 decomposition in gas phase. The role of aluminium is to contribute for larger energies in both primary and diffusion flame zone, the heat generated accelerates the surface reactions further. Another interesting topic is nano-oxides of iron, since nanosize contribute for definite increase in burn rate, but the disadvantage of agglomerations both at mixing level and combustion level needs to be addressed. Several strategies are suggested, with the most significant ones being co-precipitation with ammonium perchlorate and the utilization of dispersion agents.