The effect of alumina as an interfacial layer on the reactivity of Al/PTFE energetic composites

The exothermic behaviors of metastable intermixed composites (MICs) composed of aluminum (Al) and fluoropolymer are highly dependent on the interfacial properties. To study the effect of alumina thickness on the reactivity of Al/PTFE composites, the composites with different particle sizes have been prepared and evaluated in terms of thermal reactivity, which has been realized by experiments and molecular dynamic (MD) simulations. The kinetic parameters obtained from thermal analysis experiments are in good agreement with the simulation results. The isothermal MD simulations reveal the initial reaction process of the composite containing nanosized Al can be divided into three zones. The existence of pre-reaction zone is responsible for the lower ignition delay observed for nanosized Al in presence of PTFE. However, the chemisorption dominates the reaction of the bulk alumina, with condensed products readily to aggregating on the surface. Self-diffusion coefficient analysis indicates reducing the thickness of alumina shell by one time will increase the peak diffusion rate of oxidant atoms by 1.6 times. The molten Al atoms crossing through the core-shell interface could reach a heat transfer rate of 150 J/ps, whereas the values for model representing micron composites and bulk alumina are only 51.5 J/ps and 37.0 J/ps, respectively.