Review of Gasless Pyrotechnic Time Delays

Abstract

Gasless pyrotechnic delay compositions for time‐sequencing energetic events are reviewed. They are mixtures of powdered fuels and oxidants capable of a highly exothermic oxidation‐reduction reaction. Trends favor ‘green’ compositions targeted to replace compositions containing perchlorates, chromates, lead and barium. Thermite‐based reactions dominate but intermetallics (especially multi‐layered versions) and hybrids appear promising considering progress in self‐propagating high temperature synthesis technology. Improving computer modelling will require better description of condensed phase reactions. Progress was made with the development of “hot spot” models and expressing reactivity in terms of the number of contact points (or contact surface area) between particles. Promising processing advances include mechanochemical synthesis of reactive particle composites by arrested milling or comminution of cold‐rolled multilayer intermetallics. Dry mixing of reactive powders has made way for slurry mixing followed by spray drying.

Detailed Numerical Modeling and Simulation of Fe2O3−Al Thermite Reaction

“…As the multiple steps and diffusion effects involved in condensed-phase reactions are complex to model, simplification is necessary to make possible a mathematical analysis. As so, a single-step kinetics approximation can be applied in which the reaction rate depends on temperature and the extent of the reaction as [6,39]…”

“…Gasless reactions are more stable since the kinetic rate is not affected by pressure variations, in other words, this kind of reaction is not significantly affected by external conditions. Therefore, the reaction delay is the same whether the reaction takes place deep underwater or in a space vacuum [6].…”

“…However, most of the software available today is geared to working with gaseous reactions or reactions with a small amount of condensed phase. Most of them work with thermochemical equilibrium models, as CEA (Chemical Equilibrium with Analysis) from NASA [24,25], and they fail to converge for the reaction of compositions with a high concentration of solid species [6].…”

Nanothermites: A short Review. Factsheet for Experimenters, Present and Future Challenges

“…Nanothermites and their derivatives can be also used as fast burning compositions for short pyrotechnics delays [109], with time bases ranging from milliseconds to microseconds per centimeter. The slowest fast delay systems could be prepared from gasless nanothermites such as Al/ Cr 2 O 3 [110,111], Al/NiO [112], or red P/Fe 2 O 3 [113].…”

Study of gasless compositions used in time-delay elements

“…According to Charsley and Chen [4], the term ''gasless'' relates to compositions that generate up to 10 cm 3 of gases per g of mixture. This feature limits the adverse effect of pressure on the stability of the combustion process [5].…”