Environmentally Benign Energetic Time Delay Compositions: Alternatives for the U.S. Army Hand-Held Signal

摘要

Pyrotechnic delays are used to provide reproducible time intervals between energetic events. The simplicity and low cost of these “chemical timers” make them advantageous for inexpensive munitions such as hand grenades and signaling devices. For example, U.S. Army hand-held signals (HHS) use a pyrotechnic delay element to properly time the expulsion of illumination or smoke payloads once the rockets reach their apex. These items and other munitions use delay compositions containing chromates, perchlorates, and heavy metals. Over the last three years, our division has been working to develop environmentally benign replacement compositions for use in the U.S. Army hand-held signal. The large thermal mass of the HHS delay housing, combined with the long burning time requirement and short burning path, made it particularly difficult to develop suitable replacements. Many candidate compositions either burned too quickly or were quenched in this high heat loss environment. However, some of these systems, such as Si/Bi2O3/Sb2O3 and Ti/C-3Ni/Al may be suitable for other applications including grenade fuzes. Ultimately, two systems were found to meet the HHS delay time requirement (5-6 s, 7-8.5 s/cm). The first, W/Sb2O3/KIO4/calcium stearate, was shown to operate across a wide range of inverse burning rates, 2-15 s/cm. The second system, B4C/NaIO4/PTFE, proved even more versatile (1.3-20.8 s/cm). In this article, we describe the course of research throughout the program and discuss the general challenges associated with the development of new energetic time delay compositions.