Enhanced combustion and hydrophobic performance of aluminum micro-particles coated with high-energy fluorine-containing materials

Fluorine-containing compounds have proven to be effective coating materials for enhancing the combustion efficiency of aluminum micro-particles (Al MPs). However, these compounds are usually low-energy polymeric materials, which may inevitably diminish the overall energy density of propellants or explosives. This study introduces a two-step coating strategy using fluorinated energetic small-molecule 2-NCF to coat Al MPs, employing FeCl₃ as an intermediate layer. Compared to pristine Al MPs, 2-NCF coated Al MPs can reduce the ignition delay from 36 ms to 3 ms and shorten the time to maximum flame area from 551 ms to 114 ms, accompanied by intensified sparking combustion. Thermal analyses demonstrate that the energetic 2-NCF induces localized micro-explosions to disrupt the alumina shell, and the fluorinated segments produced by 2-NCF react with the aluminum, followed by β-AlF₃ to α-AlF₃ phase evolution, which sustains oxygen penetration for complete aluminum core oxidation to release more energy. The 2-NCF coating concurrently enhances hydrophobicity of Al MPs, elevating contact angles from 0° to 120°. This coating can effectively block water penetration and prevent hydrolysis of the inner aluminum during long storage. This work demonstrates the potential of 2-NCF as an excellent high-energetic coating material to enhance the combustion and hydrophobic performance of aluminum powder.