Stable aluminum-lithium alloy fuels for solid propellants by facile surface modifying

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As a highly reactive metal fuel, aluminum–lithium (Al-Li) alloy is an ideal candidate for replacing Al powders in solid propellants. However, the Li solid solution and AlLi compounds on the surface of Al-Li alloy powders display high reactivity, which can react with a large number of organic and inorganic reagents. Thus, the incompatibility of Al-Li alloy with other components of propellants makes it difficult to be further applied in propellants. In this study, surface-modified Al-Li alloy powders (Li content of 5 wt%) with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS17) were prepared by a facile self-assembly method, which made the alloy powders super-hydrophobic. The results of SEM, XPS and FIB-TEM show that the surface of Al-Li alloy powder is well-coated by an evenly distributed FAS17 layer. Due to the fluoroalkyl on the surface of the powders, the water contact angle increased by 91°and the intensity of the reaction between alloy powders and water is significantly reduced, which results in improved compatibility with other components of propellants.Meanwhile, the propellant grain of surface-modified powders had fewer defects than the sample before coating, and showed original excellent combustion performance. The average combustion pressure and pressurization rate increased by ∼114 kPa and ∼8613 kPa/s, and the steady burning rate increased by 0.24 mm/s. Therefore, the surface-modified Al-Li alloy powders with FAS17 are expected to be an attractive candidate as a highly active and stable fuel in solid propellants.