Scientific Technical Review

In the past few years, we have witnessed that due to the pandemic and wars, some countries have limited their export of various ingredients. The request has been made to create a time delay pyrotechnic composition with easily accessible ingredients. For that purpose, black powder with addition of phenol formaldehyde resin was a possible solution. This study aims to show an optimization of the ratio in the fuel-oxidant mixture and how this ratio influences the properties of pyrotechnic compositions. The stoichiometric ratios were determined by using the oxygen balance (OB) and pyro valence (PV) values. The linear burning rate was measured using a VOD 811 measuring system for some typical compositions which were pressed into aluminium tubes. The calorimetric bomb was used in the experiments with an inert gas supply to determinate the heat of reaction and the closed-vessel test was used to measure the production of gaseous products. The theoretical maximum density was calculated using ingredients’ density measured with gas pycnometer ULTRAPYC 5000 with an inert gas supply nitrogen or helium. After these tests, it was concluded that pyrotechnic composition with more than 25 wt.% of charcoal does not satisfy requirements for a gas producing pyrotechnic composition. The minimal requirements can be satisfied with pyrotechnic compositions that consist of 75-80 wt.% of potassium nitrate, 5-15 wt.% of charcoal, 5-10 wt.% of sulphur and remaining 5 wt.% comprising of phenol-formaldehyde resin.

Key words: time delay pyrotechnic composition, charcoal, theoretical maximum density, heat of reaction, linear burning rate, gas producing composition.

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