Altering Agglomeration in a Composite Propellant with Aluminum-Silicon Eutectic Alloy

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 degrees 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.