Pyrotechnic delays are used to introduce a time interval into the firing train to properly sequence firing of fireworks, delay firing of ejection charges (such as in model rockets), or to introduce a delay between triggering a smoke signal or hand grenade and its explosion. Typical delay times range between several milliseconds and several seconds. While current delay compositions are effective and have been proven over years of use, the heavy metals, chromates, and perchlorates they contain are toxic. Further, these compositions are generally abrasive and it is difficult to press them to the highly consolidated density required for desired performance, without the use of excessive pressure and excessive wear of the production tooling. Variances in pressing lead to unpredictability in the delay. The use of aluminum and zinc housings for the compositions introduce further variability as these materials may serve as heat sinks and capture a portion of the heat necessary to excite the charge.
Army researchers have developed a novel delay composition which is easily pressed into a housing, does not contain environmentally hazardous materials, and burns hot, but slow enough to provide predictable, relatively long delays. The composition includes boron carbide, sodium periodate, and PTFE. Boron carbide is a benign ceramic material with a high-melting point which acts as the fuel in the mixture. Sodium periodate is the oxidizer and PTFE acts as both an oxidizer and lubricant to provide better packing characteristics.
Parties interested in this technology may also want to look at the Army’s related US patent 9,193,638.
- Composition exhibits repeatable, stable burn rates per military specifications
- Burn rate can be controlled by varying the loading pressure, mixture, and particle size of the chemicals
- Composition is readily ignited by black powder, a typical igniter material that has a relatively low burning temperature and is used in current military hand-held signal delay elements
- Decreases lot-to-lot variability in compositions
- US patent 9,255,040 available for license
- Potential for collaboration with Army researchers