Sb₆O₁₃ and Bi₂O₃ as Oxidants for Si in Pyrotechnic Time Delay Compositions

Abstract

Lead and its compounds in detonator time delays are being phased out owing to environmental and health concerns. It was found that changing from the conventional rolled lead elements to rigid aluminium tubes caused a significant decrease in the burn rate. It also impaired ignitability, especially of slow burning compositions such as SiBaSO4. Consequently, potential alternatives for the latter and also the fast burning SiPb3O4 system were sought. Bi2O3, prepared by thermal decomposition of bismuth subcarbonate, gave fast burning compositions with silicon as fuel (155 mm s−1 with 20% Si). This system was ignitable by the spit of a shock tube. The SiSb6O13 system required an initiating composition and yielded slow burning compositions. The lowest sustainable and reproducible burn rate in lead tubes, in the absence of additives, was 4.8 mm s−1. In lead tubes, it was possible to reduce the burn rate further by adding fumed silica: A composition obtained by adding 10% fumed silica (add‐on basis) to a 10% Si–90% Sb6O13 composition still burned reliably at a burn rate of 2.3 mm s−1.

The effect of Si–Bi2O3 on the ignition of the Al–CuO thermite

“…decided to use the fastest burning composition instead. According to Kalombo et al [27], it contains 20 wt % silicon. The effect of particle size was studied using these compositions and the results are listed in Table 3.…”

“…Micron Bi 2 O 3 was prepared by thermal decomposition of bismuth basic carbonate at 460 °C using the method described by Kalombo et al. [27].…”

“…The filling of the delay elements and the measurement procedures used were similar to those previously described by Kalombo et al [27].…”

“…In fact, Moore et al [24] showed that even a partial substitution ( 20 wt %) of micron-sized fuel in the Al + MoO 3 thermite is sufficient to reduce the ignition delay times by up to two orders of magnitude and to dramatically increase the combustion velocity. This communication explores further sensitization of the Al + CuO thermite reaction [25] by the fastburning Si + Bi 2 O 3 pyrotechnic composition [26,27]. DTA ignition studies are used to show that the ignition temperature can be reduced significantly even when micron-sized aluminium fuel is retained.…”

Advances Toward the Development of “Green” Pyrotechnics

“…Thermal conductivity of the housing used may have a substantial influence on the burn rate of a given pyrotechnic delay mixture. Focke indicates that Si/Bi 2 O 3 -and Si/Sb 6 O 13 -based delay mixtures encased in aluminum housings have a reduced burn rate on the order of 20-50% compared to the burn rates observed when these mixtures burn in lead housings [61]. This phenomenon is believed to be attributed to the large thermal conductivity of aluminum, which is about six times that of lead.…”