Strontium molybdate as a replacement for barium chromate in the traditional tungsten time delay: an exploration of reaction mechanisms for design of pyrotechnic delays

In this work, replacement of barium chromate (BaCrO4) in the traditional tungsten delay (W/BaCrO4/KClO4/Diatomaceous Earth (DE)) with strontium molybdate (SrMoO4) is explored both mechanistically and as an environmentally friendly alternative to currently fielded time delays. Delay performance and aging characteristics are examined at similar diameters (4.7 mm) to common delay housings. Measured maximum combustion temperatures ranged from 1507 K to 1628 K as a function of tungsten content. The measured combustion velocities ranged from 1.36 to 29.87 mm/s in 4.7 mm inner diameter aluminum housings for the alternative system. Activation energies were determined for both the traditional tungsten delay and the alternative formulation and ranged from 74.6 to 240.5 kJ/mol. The maximum measured gas production was 4.1 mL/g for all alternative formulations. Combustion products were characterized with powder X-ray diffraction and are relatively benign based upon known compound information and current regulations. Lastly, based on the data, general reaction mechanisms for pyrotechnic time delays are discussed toward design decisions of a good time delay.