Dynamic Covalent Surface Engineering of Highly Reactive Al-Li Alloy Powders for Propellant Application

Organic functionalization of highly reactive metal powders is of great significance for chemistry and materials science yet remains a critical challenge. Herein, the interfacial self-polymerization cross-linking strategy based on boroxine chemistry is proposed to construct a functional dynamic covalent network on Al-Li alloy powders. The 4-hydroxyphenylboronic acid (HPBA) monomers undergo spontaneous dehydration and interfacial polymerization to form a trimer structure with boron-oxygen (B-O) dynamic covalent bonds in ethyl acetate solvent under vacuum and thermal conditions. During subsequent desolvation process, the HPBA trimer is further cross-linked through multimer and reactive phenolic hydroxyl groups. Dynamic B-O bonds in the boroxine structure endow the network with intrinsic self-healing capability. DFT calculation and AIMD simulation indicate that boron atoms in HPBA trimer undertake sp³ hybridization to form robust B-O-Al/Li covalent bonds with 200.167 kJ mol^-1 adsorption energy. Desolvation can generate a controllable surface morphology for the network to efficiently block corrosive media transport. This organic functionalization strategy endows Al-Li alloy-based composite solid propellants with outstanding mechanical performance (2.342 MPa tensile strength) while improving the combustion heat of Al-Li alloy fuel to 30.648 MJ kg^-1 with 3.2% enhancement.