Thermodynamic Modeling of Pyrotechnic Smoke Compositions

Some of the most effective visible obscurants for military applications are toxic or incendiary or present serious logistical complications. Sustainable alternatives are needed to mitigate the risks of human exposure and environmental contamination. The FactSage 6.4 software package was used to model the thermodynamics of pyrotechnic smoke compositions based on boron carbide, hexachloroethane, and phosphorus. The computational results are shown to be relevant in light of prior experimental observations. Boron phosphide is proposed as a benign source of phosphorus for next-generation pyrotechnic smoke compositions. The thermodynamics of the BP–KNO₃ system have been studied computationally. The results indicate that certain stoichiometries should produce elemental phosphorus upon combustion. The properties of the BP–KNO₃ system are examined considering the functional requirements of smoke munitions

Demonstration of the B₄C/NaIO₄/PTFE Delay in the U.S. Army Hand-Held Signal

A pyrotechnic time delay based on boron carbide has been demonstrated as a viable replacement for the perchlorate- and chromate-containing formulation currently used in U.S. Army hand-held signals. Tests involving fully assembled hand-held signal rockets were conducted to evaluate the characteristics of the B₄C/NaIO₄/PTFE delay system in an operational configuration. The delay times observed in such dynamic tests were substantially shorter than those expected from prior static testing, necessitating the use of very slow-burning compositions to achieve the desired 5–6 s dynamic delay time. The behavior of the system at extreme temperatures (−54 and +71 °C) was also evaluated, confirming its reliability and safety. Impact, friction, and electrostatic discharge tests have shown that the boron carbide-based delay is insensitive to unintended ignition. TGA/DSC analysis indicated an ignition temperature of 475 °C, well above the decomposition temperature of NaIO₄ and above the melting points of NaIO₃ and PTFE

Performance and Aging of Mn/MnO₂ as an Environmentally Friendly Energetic Time Delay Composition

The Mn/MnO₂ reactive system was investigated as a suitable replacement for the traditional W/BaCrO₄/KClO₄/diatomaceous earth delay composition. The delay performance, ignition sensitivity, and aging characteristics were examined in aluminum microchannels similar in diameter to common delay housings (4.7 mm). Stoichiometries with measured combustion temperatures between 1358 and 2113 K were self-sustaining with combustion velocities ranging from 2.4 to 7.3 mm s^–1. The Mn/MnO₂ system produced less gas than W/BaCrO₄/KClO₄/diatomaceous earth compositions allowing consideration for use in sealed delay housings. Accelerated aging at 70 °C and 30% relative humidity for 8 weeks resulted in no measurable loss of performance. Safety characterization showed that this composition is not sensitive to ignition by friction or electrostatic stimuli. The combustion products (as determined by X-ray diffraction) appear to be benign based on current regulations. Therefore, the Mn/MnO₂ system appears to be a suitable low gas-producing, nonsensitive, less toxic delay composition with good longevity

Synthesis and Resolution of Chiral Ruthenium Complexes Containing the 1‑Me-3-PhCp Ligand

A new ruthenium chloride complex featuring chirality derived from the face-specific coordination of the 1-Me-3-PhCp ligand has been successfully synthesized and resolved. The resolution has been achieved via the diastereomers of the (<i>S</i>)-α-methyl-benzenemethanethiolate complex (1-Me-3-PhCp)­Ru­(dppm)­{(<i>S</i>)-C­(S)­(H)­(Ph)­(Me)}. The X-ray structures of (<i>S</i>_Cp,<i>S</i>)-(1-Me-3-PhCp)­Ru­(dppm)­{C­(S)­(H)­(Ph)­(Me)} and (<i>R</i>_Cp,<i>S</i>)-(1-Me-3-PhCp)­Ru­(dppm)­{C­(S)­(H)­(Ph)­(Me)} have been determined. Racemization has been observed at elevated temperatures, but a room-temperature conversion pathway provides access to the corresponding enantiopure acetonitrile, chloride, and hydride complexes

Synthesis, Electrochemistry, and Reactivity of New Iridium(III) and Rhodium(III) Hydrides

Two new iridium hydride complexes, Cp*Ir­(2-phenylpyridine)­H (Cp* = pentamethylcyclopentadienyl) and Cp*Ir­(benzo­[<i>h</i>]­quinoline)­H, and their rhodium analogues Cp*Rh­(2-phenylpyridine)H and Cp*Rh­(benzo­[<i>h</i>]­quinoline)H have been prepared from the corresponding chlorides. The X-ray structures of Cp*Ir­(2-phenylpyridine)H and Cp*Rh­(2-phenylpyridine)­H have been determined. The electrochemistry of all four hydride complexes and the corresponding chlorides has been studied by cyclic voltammetry; all exhibit irreversible M­(III/IV) (M = Ir, Rh) oxidations. The hydride complexes are more easily oxidized than their chloride analogues, and the rhodium hydrides are more easily oxidized than their iridium analogues. The hydride complexes transfer H^– to the <i>N</i>-carbophenoxypyridinium cation at room temperature, giving mixtures of the 1,2- and 1,4-dihydropyridine products. In CD₃CN all four hydrides give these products in nearly the same ratio, which results from kinetic control; the thermodynamic ratio of the products has been calculated, and isomerization in that direction has been observed. In weakly coordinating solvents the cations left after H^– transfer catalyze this isomerization. Acetonitrile can trap these cations, slowing isomerization substantially. The X-ray structures of [Cp*Ir­(2-phenylpyridine)­(CH₃CN)]­[PF₆] and [Cp*Rh­(2-phenylpyridine)­(CH₃CN)]­[PF₆] have also been determined

Versatile Boron Carbide-Based Energetic Time Delay Compositions

Pyrotechnic time delay compositions composed of boron carbide, sodium periodate, and polytetrafluoroethylene have been developed for use in the U.S. Army hand-held signal. The new compositions were developed to replace the currently used composition that contains potassium perchlorate and barium chromate, chemicals that are facing increasing regulatory scrutiny. Static tests in aluminum hand-held signal delay housings demonstrated a wide range of available inverse burning rates (1.3–20.8 s/cm), which includes the 7–8.5 s/cm range required for hand-held signals. The roles of loading pressure, mixture stoichiometry, and component particle size are described herein

Prototype Scale Development of an Environmentally Benign Yellow Smoke Hand-Held Signal Formulation Based on Solvent Yellow 33

We report herein the development of an environmentally benign yellow smoke formulation aimed to replace the environmentally hazardous mixture currently specified for the U.S. Army’s M194 yellow smoke hand-held signal. Static ignition test measurements have identified a replacement candidate that generates a robust fountain of yellow smoke, burning for 15 s from a consolidated cardboard tube configuration. This new formulation meets the burn time parameters outlined in the military requirement and is composed entirely of dry, powdered, solid ingredients without the need for solvent-based binders. In addition, this formulation was found to have relatively low sensitivity to impact, friction, and electrostatic discharge

Versatile Boron Carbide-Based Visual Obscurant Compositions for Smoke Munitions

New pyrotechnic smoke compositions, containing only environmentally benign materials, have been demonstrated to produce thick white smoke clouds upon combustion. These compositions use powdered boron carbide (B₄C) as a pyrotechnic fuel, KNO₃ as a pyrotechnic oxidizer, and KCl as a combustion temperature moderator. Small amounts of calcium stearate and polymeric binders may be added to moderate burning rate and for composition granulation. Prototype tests involving three preferred compositions were conducted in end- and core-burning grenade and canister configurations. Smoke release times ranged from 3.5 to 70 s for the grenades and from 8 to 100 s for the canisters. Notably, any desired smoke release time within these ranges may be obtained by fine adjustment to the calcium stearate content of the compositions and/or small changes to the device containers. Aerosolization efficiency and quantitative performance, as determined by smoke chamber measurements, remain consistent regardless of smoke release time. Impact, friction, and electrostatic discharge tests show that the compositions are insensitive to accidental ignition and are safe to handle