Stabilization of AlH₃ Crystals by the Coating of Hydrophobic PFPE and Resulted Reactivity with Ammonium Perchlorate

Abstract

Aluminum hydride (AlH 3 ) is a promising fuel component of solid propellant, but its stabilization is still challenging. Herein, surface functionalization of hydrophobic perfluoropolyether (PFPE) followed by ammonium perchlorate (AP) coating has been implemented. In particular, AlH 3 @PFPE@xAP (x = 10, 30, 50, or 64.21%) composites (AHFPs) were prepared by a spraydrying technique. The PFPE-functionalized AlH 3 with a hydrophobic surface shows an increased water contact angle (WCA) from 51.87°to 113.54°. Compared with pure AlH 3 , the initial decomposition temperatures of AHFPs were increased by 17 °C, and the decomposition properties of AP in the AHFPs were also enhanced with significantly decreased peak temperature and fairly increased energy output. Moreover, the decomposition induction time of AHFPs-30% was improved by almost 1.82 times that of raw AlH 3 , which indicates that the coatings of PFPE and AP could improve the stability of AlH 3 . The maximum flame radiation intensity of AHFPs-30% was 21.6 × 10 3 , which is almost 7.71 times that of pure AlH 3 (2.8 × 10 3 ).

High-Energy Composite Fuels with Improved Combustion Efficiency by Using AlH3 Embedded with Al Particles

“…Moreover, they have impressive thermal and oxidative stability. Our previous study also indicated that PFPE-functionalized AlH 3 showed a significant increase in both water contact angle and energy output . However, there have been limited reports on research conducted on the inclusion of stabilized AlH 3 in solid propellants.…”

“…The corresponding peak temperatures of AP decomposition in pure AlH 3 -based propellants (SP11) are 319.6 and 363.3 °C, and the exothermic peak temperature is 367.5 °C, which is reduced by 4.1, 16.8, and 14.5 °C, respectively. These results indicate that the hydrogen of AlH 3 can promote the rapid decomposition of AP, mainly because the H 2 produced by the decomposition can take away the material on the surface of AP to promote the decomposition . Upon comparing the thermal decomposition process of propellants containing AHAPs (SP13) and AHAPs-F (SP14) with that of the mechanically mixed component propellant (SP12), it was observed that the low- and high-temperature decomposition peak temperatures of AP in SP13 increased by 6.2 and 3.8 °C, respectively, indicating that the stability of AP can be slightly enhanced after embedding Al and AP.…”

“…Therefore, the most widely studied aspect of AlH 3 is the thermal decomposition properties at lower heating rates, but the corresponding research contents on AlH 3 -based propellants are not so rich. ,− The reason is that the less stability and poor compatibility of AlH 3 limit its application in propellants, which results in spontaneous decomposition and failure of the propellants . Much effort has been made to solve these problems, including coating, passivation, doping, and optimization of synthesis conditions to obtain better crystal quality. ,− Moreover, the structures with defects and cracks will promote the formation of hydrogen vacancies, and these vacancies are the source of Al-phase nucleation sites that accelerate the decomposition reaction of AlH 3 . Therefore, the coating method has a greater chance of improving its thermal stability and compatibility.…”