Role of Pressure and Aluminum Size in Solid Propellant CCP Generation

Aluminum combustion in solid propellants generates condensed products leaving the burning surface. The population of this particles is quite wide, spanning from smoke-oxide to molten metal drops. Their properties depend upon both intrinsic propellant features and combustion conditions (e.g. composition, microstructure, combustion pressure, and propellant burning rate). In propellants, aluminum is typically used in the shape of a micrometric powder. This class of energetic materials produces spherical agglomerates having the size between some tens to few hundreds of micrometers. When the metal fuel turns to nanometric, flake-kind aggregates emerge from the burning surface. Some macroscopic properties, such as the burning rate, are affected. This paper presents some results obtained from a set of aluminized propellants based on inert binder (hydroxylterminated polybutadiene) and ammonium perchlorate. The effect of both powder size and pressure is explored in terms of ballistics and condensed combustion residues. A nonstraightforward trend with pressure emerges when the condensed combustion products of propellants containing micro-aluminum and nano-aluminum are compared.