Synergistic Enhancement on Ignition and Combustion Properties of Boron via Viton Core-Shell Coating.

Abstract

The high gravimetric (58.74 kJ/g) and volumetric (137.45 kJ/cm3) heat values loaded in boron (B) offer significant potential for application in solid propellants and explosives. However, the high melting (2076 °C) and boiling (3927 °C) points of boron powder and the low melting point (450 °C) of oxidation products affect the energy performance and application of boron. Fluorine-containing polymers have high oxidation potential and excellent mechanical properties and can produce expectant gaseous products through the combustion reaction with boron oxide, but research examining the interaction between purified boron powder and fluoropolymers and the optimal selection of the fluoropolymer remains scarce. Herein, the binding energy between typical fluoropolymers [Viton, polyvinylidene fluoride, poly(vinylidene fluoride-co-chlorotrifluoroethylene), and vinylidene fluoride] and boron was calculated via molecular dynamics simulations, which shows that Viton is an appropriate candidate for coating boron powder. In the experiment, The Bw@Viton core-shell composites were prepared using Viton as the coating layer, and boron powder was pre-purified with acetonitrile. Its structure, thermal properties, ignition, and combustion characteristics were then characterized. The results revealed successful removal of the oxide layer, and the hydrophobicity was significantly improved after Viton coating. Purification and coating synergistically enhance the energy release of boron powder, and the composites demonstrated excellent thermal, ignition, and combustion performances. In particular, the heat of oxidation and heat of combustion were increased by 26.6 and 32.7%, respectively. The ignition delay time was reduced by 53.2% compared to raw boron. A prospective reaction mechanism between boron and Viton is thus proposed.