Review of Gasless Pyrotechnic Time Delays

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.