Energetic Characteristics of Aluminum/Graphene Oxide Composites with Optical Activation

Aluminum (Al), with high specific energy density (31 kJ/g) and earth abundance, is a widely used fuel in solid energetic materials to generate heat, gas, and thrust for applications ranging from space propulsion and pyrotechnics to microelectromechanical systems (MEMS). Al-based energetic materials are typically ignited at a single point by a hotwire, flame, or spark. In comparison to point ignition, optical Xe flash ignition occurs across the illuminated area and provides high heating rates, potentially increasing the energy release rate and changing the reaction dynamics of Al. However, micron-sized Al (μ-Al) particles, which are widely used in practical applications, cannot be ignited by a low-energy Xe flash due to poor light absorption properties and high ignition temperature. In this work, we demonstrate that graphene oxide is an effective additive to enhance the optical ignition and combustion properties for μ-Al particles (3–4.5 μm). The results indicate that 3 wt % of GO addition is sufficient to enable the flash ignition of μ-Al particles, for which the normalized minimum ignition energy can be reduced to 44% with 30 wt % of GO addition. The constant-volume combustion test results also show that 20 wt % of GO addition can optimally enhance the combustion performance after flash ignition. The Al/GO (80/20 wt %) composites are superior to the commonly used Al/nanosized metal oxide in terms of higher Al content, lower minimum optical ignition energy, higher peak pressure, faster pressurization rate, and longer overpressure duration during combustion. The energetic nature and enhancing mechanisms of GO were revealed by thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and reactive molecular dynamics (RMD) simulation. Optically activated GO was experimentally shown to undergo photothermal disproportionation and oxidation reactions, which release heat to initiate the oxidization of Al by air and generate gaseous products to reduce the agglomeration of the solid-phase oxidation products and promote the pressure rise during combustion. The RMD simulation results further confirm that the addition of GO promotes the oxidation of μ-Al particles by exhibiting catalytic effects on the dissociation of oxygen molecules and providing a direct diffusion pathway for the dissociated O atom to reach and react with Al. Overall, the enhanced effects of GO can be attributed to the coupling heat release, catalytic effect, and gas generation. The low mass density of GO can also effectively advance the application of μ-Al particles as energetic materials via the form of Al/GO composites with the advantage of preserving higher Al content, reducing dead mass, and maintaining the high energy density. All of these results confirm that GO is an effective additive to enhance the energetic performance of Al with optical activation.