In situ investigation of combustion behaviors of Al and Al-2.3Li particles in solid composite propellants using high-speed synchrotron X-ray radiography: Effect of Al-2.3Li alloy on agglomeration inhibition

Due to the high energy density and affordability, Al is widely used in energetic materials. However, the agglomeration of Al particles during combustion significantly decreases propellant combustion efficiency. With reduced agglomeration and higher combustion enthalpy, Al-2.3Li alloy presents a promising alternative. In this study, we prepare propellants with various Al-2.3Li concentrations and examine their thermal behaviors using TGA/DSC and an oxygen bomb calorimeter, as well as combustion kinetics through a CCD line-scan camera, high-speed photography, fast X-ray imaging, and condensed combustion products (CCPs) analyzed with SEM and a laser diffusion system. Compared to pure Al, Al-2.3Li shows higher combustion heat and efficiency, with a shorter ignition delay and a notable decrease in the D₅₀ of CCPs. The evolution cycles of bubbles within molten Al/Al-2.3Li droplets were observed using high-speed synchrotron X-ray radiography. The agglomeration pathways of Al and Al-2.3Li differ significantly, and their combustion mechanisms were elucidated. This work demonstrates that Al-2.3Li is a high-energy-density metallic fuel candidate with superior combustion performance in AP/HTPB propellants, offering an approach for binary alloy alternatives. The use of fast X-ray imaging to capture agglomeration processes provides a deeper sight for studying AP/HTPB propellant combustion mechanisms.