The influence of carbon hindering and alumina layer on PTFE-Al and PTFE-Ti reactive materials

This study investigates the influence of surface oxidation layers and carbon-hindering effects on the reactivity of PTFE-based structural reactive materials (SRMs) incorporating nano-aluminum (nAl) or micron-sized titanium (μTi). Two composite systems, nAl-PTFE and μTi-PTFE, were prepared via uniaxial compaction and characterized using simultaneous DSC–TGA together with ex-situ XRD at selected temperatures to resolve their thermochemical pathways. Dynamic impact reactivity was then quantified using a synchronized Split Hopkinson Pressure Bar (SHPB) coupled with high-speed optical and infrared diagnostics. Under static conditions (DSC), nAl-PTFE exhibited a sharp exothermic event and extensive fluorination above 700 °C, forming predominantly AlF₃, while no crystalline residual Al was detected by XRD. In contrast, μTi-PTFE showed a broader, relatively weak exotherm dominated by TiO₂ formation with only minor TiC. Under impact loading (SHPB), nAl-PTFE ignited earlier than both μAl-PTFE (from prior work) and μTi-PTFE, reacting after the second loading wave and generating a high-intensity fireball with peak temperatures of ∼750 °C. By contrast, μTi-PTFE demonstrated higher mechanical robustness, strain hardening, delayed ignition, and significantly lower peak temperatures (∼250 °C). The pronounced reactivity of nAl-PTFE is attributed to its high oxide-to-metal ratio, enhanced susceptibility to fluorination, and Al₂O₃'s ability to serve as an effective carbon sink during rapid heating, mitigating carbon-induced reaction hindrance. These findings highlight the coupled roles of particle size, oxidation layer chemistry, and carbon mobility in governing SRM performance and provide design guidelines for optimizing fluorinated energetic composites for impact-driven applications.