Linking molecular level chemistry to macroscopic combustion behavior for nano-energetic materials with halogen containing oxides

Abstract

Coupling molecular scale reaction kinetics with macroscopic combustion behavior is critical to understanding the influences of intermediate chemistry on energy propagation, yet bridging this multi-scale gap is challenging. This study integrates ab initio quantum chemical calculations and condensed phase density functional theory to elucidate factors contributing to experimentally measured high flame speeds (i.e., >900 m∕s) associated with halogen based energetic composites, such as aluminum (Al) and iodine pentoxide (I2O5). Experiments show a direct correlation between apparent activation energy and flame speed suggesting that flame speed is directly influenced by chemical kinetics. Toward this end, the first principle simulations resolve key exothermic surface and intermediate chemistries contributing toward the kinetics that promote high flame speeds. Linking molecular level exothermicity to macroscopic experimental investigations provides insight into the unique role of the alumina oxide shell passivating aluminum particles. In the case of Al reacting with I2O5, the alumina shell promotes exothermic surface chemistries that reduce activation energy and increase flame speed. This finding is in contrast to Al reaction with metal oxides that show the alumina shell does not participate exothermically in the reaction.

Molecular dynamic simulation of thermite reaction of Al nanosphere/Fe2O3 nanotube

“…Shimojo et al [29][30][31] used the first-principles molecular dynamics to study electronic transportation during reaction process of Al/Fe 2 O 3 nanothermite. Farley et al [32] integrated ab initio quantum chemical calculations and condensed phase density functional theory to illustrate reasons leading to experimentally measured high flame speeds, and found that activation energy correlated with flame speed rather than heat of combustion. Furthermore, Nguyen et al [33,34] reported molecular dynamic study for Al/Pd core-shell nanoparticles and reaction rate is determined by the solid-state diffusion of Al atoms.…”

Ignition and Combustion Characterization of Ca(IO3)2‐based Pyrotechnic Composites with B, Al, and Ti

“…In addition, to their high iodine content, these oxidizers have a high enthalpy of reaction and high flame temperature when used as part of an Al-based pyrolant mixture (Table S1). Notably, Al/I 2 O 5 has the highest iodine content (67 wt-%) and a high reactivity [19,20]. However, the hygroscopic nature of I 2 O 5 can negatively impacting reactivity.…”

Development of flexible, free-standing, thin films for additive manufacturing and localized energy generation

“…7 Because these high bulk density films have limited porosity, gas generating oxidizers may inhibit the diffusion of energy through the film and hinder flame speed. This makes KClO 4 a desirable oxidizer 16 because of its high oxygen content and its low gas generation. Farley et al 6 also showed that Al + KClO 4 produced orders of magnitude slower flame speeds in comparison to Al with other solid oxidizers (e.g., silver iodate, calcium iodate and iodine pentoxide ) indicating that Al + KClO 4 is not particularly reactive.…”

“…Farley et al 16 examined the combustion properties of Al + KClO 4 and found this mixture to be relatively non-gas generating compared to thermites such as Al + I 2 O 5 , 16 Al + MoO 3 , 8,17 and Al + CuO. 7 Because these high bulk density films have limited porosity, gas generating oxidizers may inhibit the diffusion of energy through the film and hinder flame speed.…”

“…Energy propagation was evaluated from flame speed measurements that provided an empirical quantification of energy release rates available from the reactions. [7][8][9]16,[21][22][23] These experiments were complemented by thermal equilibrium simulations performed using REAL code software to calculate combustion properties. Additional experiments were performed to characterize the reaction kinetics using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).…”