Effect of Organic Fluoride on Combustion Performance of HTPB Propellants with Different Aluminum Content

Aluminum is an important contributor to energy of solid propellants. Completeness of aluminum combustion has key effect on the release of energy. In this paper, hydroxyl-terminated polybutadiene (HTPB) based propellants with aluminum content from 16% to 24% were prepared with a kind of organic fluoride (OF). Meanwhile, propellants without OF were also prepared as a comparison. The theoretical specific impulse and the heat of explosion of these propellants were calculated and measured, respectively. The particle size, morphology and elemental composition of the condensed combustion products for these propellants were characterized by laser measurement of particle size, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The burning rates of propellants were tested by CCD line-scanning camera and a high-pressure chamber measurement system. The high-speed photographic system was used to study the agglomeration process of the melting aluminum particles on the propellant burning surface. The results indicate that with increasing aluminum content, both the theoretical specific impulse and the measured heat of explosion show a trend of increasing until an aluminum content of 20%. The large particle size and residual active aluminum in the condensed combustion products increase with increasing aluminum content in the propellants, but decrease significantly after addition of OF. Under the same pressure, the burning rates of the blank and OF propellants decrease with increasing aluminum content, but the burning rates of OF propellants are slightly higher than those of the blank propellants. For the propellants with OF, the melting aluminum particle on the burning surface is less agglomerated and brighter, meaning more complete aluminum combustion.