Pioneering Insights into the Reaction Kinetics of Metastable Intermolecular Composites Based on Metal Fluorides: Virtually non-existent condensed Phase Combustion Products and Ultra-Efficient Reactivity.

As a typical representative of Metastable intermolecular composites (MICs), the energy release of nano-thermites relying on aluminum-oxygen reaction is limited by the formation of high boiling point condensed phase products. Low pressure output performance constitutes another pivotal factor influencing their efficacy. In this work, metal fluorides BiF at different scales were incorporated into nano-thermites as oxidants, thereby facilitating the tunability of the released energy. The boiling points of all resultant reaction products fall below the combustion temperature, theoretically abolishing the agglomeration of condensed-phase products, thus preventing the entrapment of active metals. Additionally, it facilitates the smooth conduction of heat flux, thereby averting losses in biphasic flow dynamics. The n-Al/n-BiF system exhibits a significant amplification in reactive kinetic properties in stark contrast to the n-Al/n-BiO system. The reduction in ignition threshold is ascribed to a novel reaction kinetics mechanism within the n-Al/BiF system. The highly electronegative fluorine within BiF corrodes the AlO shell, inducing a "pre-ignition" reaction. The application of Density Functional Theory (DFT) evaluations has further corroborated the n-Al/n-BiF system's preeminence in electron transfer capacity between the oxidizing agent and fuel, thereby furnishing an molecular-electronic basis for its potent reactive kinetic properties.