Boron has been regarded as a promising high-energy fuel due to its high volumetric and gravimetric heating values. However, it remains challenging for boron to attain its theoretical heat of combustion because of the existence of its native boron oxide layer and its high melting and boiling temperatures that delay ignition and inhibit complete combustion. Boron combustion is known to be enhanced by physically adding fluorine-containing chemicals, such as fluoropolymer or metal fluorides, to remove surface boron oxides. Herein, we chemically functionalize the surface of boron particles with three different fluoroalkylsilanes: FPTS-B (F3-B), FOTS-B (F13-B), and FDTS-B (F17-B). We evaluated the ignition and combustion properties of those three functionalized boron particles as well as pristine ones. The boron particles functionalized with the longest fluorocarbon chain (F17) exhibit the most powerful energetic performance, the highest heat of combustion, and the strongest BO2 emission among all samples. These results suggest that the surface functionalization with fluoroalkylsilanes is an efficient strategy to enhance boron ignition and combustion.

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The ignition sensitivity of ammonium perchlorate (APC) and ammonium periodate (API) was analyzed in terms of crystalline structure, thermal and mechanical properties, and electronic structure using density functional theory (DFT) calculations. API is more rigid, with a higher bulk modulus (K) of 25.87 GPa compared with 21.42 GPa for APC. On the other hand, the shear moduli (G) are similar, 9.75 GPa for API and 9.42 GPa for APC. With higher bulk moduli and similar shear moduli, API will experience more shear than compression in situations such as friction. Also, API presents slightly more lateral deformation than APC, with Poisson’s ratio (ν) of 0.333, compared with 0.308 for APC, and contributes to a less consistent deformation in terms of the crystal lattice. A less stable lattice structure will contribute to greater ignition sensitivity of API compared with APC. The electronic density of states (DOS) analysis showed that API also has a more ignition sensitive profile with a band gap of a semiconductor type, Δg = 2.92 eV, while APC is a typical insulator with a band gap of Δg = 6.21 eV. The analysis of the electronic structure coupled with overall higher anisotropy (shown by calculated elastic constants) could induce ignition of API in a solid phase, whereas the greater stability of APC results in a multiphase ignition mechanism. Results shown here demonstrate important properties that influence the safe handling and use of energetic materials. The observed similarities in structural, mechanical, and thermodynamic properties of API and APC and the considerably large differences in electronic properties indicate that the latter is the key to the higher ignition sensitivity of API.