While Al-alloys are generally employed for their structural and mechanical properties, the low-level inclusion of secondary metals may make such materials advantageous in propellant formulations and have not been fully considered. In this work, the Al-Si eutectic alloy was evaluated as a potential solid composite propellant fuel. Equilibrium calculations showed that Al-Si increases the adiabatic combustion temperature and decreases the molecular weight of the products, which in turn yields a higher theoretical specific impulse on the order of 2.5 seconds over Al. Propellant strands (71/14/15 wt.% AP/HTPB/fuel additive) were burned in a Crawford pressure bomb at various pressures, and videography was used to interpolate burning rate as a function of pressure. Additionally, a plume traversing quench disc was used to capture the products above the propellant surface in order to observe and quantify coarse product agglomeration. Analysis of the propellant products was performed via optical microscopy and X-ray diffraction. It was observed that for the Al-Si eutectic alloy, the mean coarse agglomerate size was increased over Al. This is likely attributed to the high fluidity of molten Al-Si. Recent studies have indicated that the low-level inclusion of fluoropolymers into aluminum through mechanical activation (MA) can significantly reduce the agglomeration size as well as increase combustion efficiency near the surface. Therefore, MA 70/30 Al-Si/polytetrafluoroethylene (PTFE) was also assessed in order to decrease agglomeration. It was observed that the low-level fluoropolymer inclusion did reduce agglomeration and increased combustion efficiency. Therefore, Al-Si is a viable fuel for composite propellants and should be evaluated in other energetic formulations and applications.
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