Altering agglomeration in a composite propellant with aluminum–silicon eutectic alloy

Abstract

Although aluminum alloys are generally employed for their structural and mechanical properties, the low-level inclusion of secondary metals and metalloids may also make alloy powders advantageous in propellant formulations and have not been fully considered. In this work, the aluminum–silicon (Al–Si) eutectic alloy, which has a lower melting point (577°C) than either constituent, was evaluated as a potential solid composite propellant fuel. Equilibrium calculations showed that Al–Si-based propellants had slightly lower theoretical ideal performance to equivalent aluminum-based propellants, with a typical specific impulse reduction of roughly 2.5 s for most mixture ratios of interest. However, if product agglomerate size could be reduced, improved performance could result. Neat and composite Al–Si/polymer powders were studied in solid propellant formulations. Burning rate experiments were performed in a windowed pressure vessel, and condensed phase combustion products were collected. It was found that the Al–Si-based propellants followed the same trends (burning rate exponent) but at a lower magnitude (burning rate coefficient) as neat aluminum-based propellants. However, the coarse product agglomeration of the Al–Si-based propellants was found to be larger than the neat aluminum-based propellants, which may be due to the high fluidity of Al–Si eutectic alloy.