Al-B alloy as a composite propellant additive: The role of B in combustion and agglomeration

Abstract

An experimental investigation was conducted to examine the effects of Al-B alloy additives on the ignition, combustion, and agglomeration characteristics of composite propellants. The properties of four Al-B alloys with different B contents (5 %, 20 %, and 50 % B) were comparatively evaluated against pure Al powder using Thermogravimetric-Differential Scanning Calorimetry, ignition research by CO₂ laser, combustion experiments under high-pressure, Scanning Electron Microscopy, and X-ray Diffraction. B addition markedly accelerates the oxidation of Al, increases the total heat release, and shortens ignition delay. Regarding combustion performance, Al-B alloy propellants exhibited higher burning rates, with the alloy containing 50 % B (Al/B = 1:1) showing the most pronounced improvement and a relatively low pressure exponent. In terms of agglomeration suppression, alloys with lower B content (e.g., 5 % B) effectively decreased particle size combustion products size. However, increased B content led to greater formation of B₂O₃ in the combustion products, whose adhesive properties promoted particle agglomeration. Considering a trade-off among ignition delay, burning rate, and agglomeration inhibition, Al-B alloy with 50 % B content demonstrates the greatest potential for enhancing the overall performance of composite propellants.