Work

Unlocking controllable ignition and combustion in onion-structured Al@Na3AlF6@AP composites through Na3AlF6 “Temperature Switch”

Year: 2025

Type: article

Abstract: • Al@Na 3 AlF 6 @AP onion-structured composites are fabricated via sequential EISA. • Ion diffusion at Na 3 AlF 6 /Al 2 O 3 interfaces enables 96.75% Al oxidation efficiency. • Na 3 AlF 6 overcomes the Aluminum ignition limitation caused by Al 2 O 3 . • Onion architecture reduces diffusion-controlled reactivity loss by 29.6%. The combustion of aluminum in solid propellants is inherently hindered by its surface oxide shell, leading to ignition delay, particle agglomeration, and low combustion efficiency. Herein, an onion-structured Al@Na 3 AlF 6 @AP composite is synthesized via a two-step evaporation-induced self-assembly process, sequentially depositing cryolite (Na 3 AlF 6 ) and ammonium perchlorate (AP) onto the aluminum surface. The Na 3 AlF 6 interlayer functions as a temperature switch inducing the transformation of the Al 2 O 3 into Al 6 NaO 9.5 at 700 °C and simultaneously exposing the active aluminum core. Therefore, the oxidation efficiency of Al@Na 3 AlF 6 is as high as 96.75 %, significantly surpassing the values achievable by pure aluminum and conventional aluminum alloys. Furthermore, the AP-encapsulated structure of Al@Na 3 AlF 6 @AP constructs a self-sustaining oxygen supply network during aluminum combustion and reduces the diffusion time of oxidative gases to the aluminum surface by 29.6 %. As a result, the size of aggregates during Al@Na 3 AlF 6 @AP combustion is approximately 10 μm, and the combustion heat (19.532 ± 0.133 MJ kg −1 ) is 8.4 % higher than that of the physically mixed sample Al@Na 3 AlF 6 /AP. The unique onion structure and Na 3 AlF 6 “Temperature Switch” both fundamentally reshape combustion kinetics, shifting the rate-limiting step from oxygen diffusion to aluminum oxidation activation.

Source: Fuel

DOI: 10.1016/j.fuel.2025.136033