A comparative study of Si-BaSO4 and Si-CaSO4 pyrotechnic time-delay compositions

Abstract

Slow burning Si-BaSO4 pyrotechnic delay compositions are employed commercially for intermediate to long time delays. However, there is very little information on this composition available in open literature. The reactivity of this composition was therefore characterized and compared to that of Si-CaSO4. The Si-BaSO4 composition supported combustion in the range of 20 to 60 wt.% Si in the bomb calorimeter. However, burning was only sustained between 20 and 40 wt.% Si in rigid aluminum tubes, with burning rates of between 8.4 and 16 mm s1. These values are comparable to those for the Si-CaSO4 system (6.9 – 12.5 mm s1). However, the CaSO4 based formulations tended to have higher energy output and produced more transient pressure compared to the barium sulfate compositions. Both formulations were insensitive to impact, friction and electrostatic discharge stimuli. The reaction products were a complex mixture that contained crystalline phases in addition to an amorphous phase. Although barium sulfate is insoluble in water and decidedly non-toxic, the reaction products produced by the Si-BaSO4 compositions were found to release soluble barium ions when contacted with water. This ranged from 50 to 140 mg per gram of barium sulfate reacted.