Performance of Mn/Bi2O3 Pyrotechnic Time Delay Compositions

Chemical time delay detonators are used widely in mine blasting applications. In order to achieve effective blasting, detonations must follow a precisely controlled timing sequence in a specified firing pattern. Silicon fuel-based pyrotechnic compositions are widely used in mining detonators and are well studied. However, some of these formulations are deemed to be problematic, as they contain heavy metals which are bio-accumulative and toxic to the environment. Therefore, there is need to explore alternative formulations which are suitable for these applications. Manganese-fueled systems are attractive due to their metallic properties and several oxidation states of the manganese fuel. This study focused on characterizing the burn properties of Mn/Bi2O3 compositions for slow to intermediate time delay applications. The compositions supported combustion in the 25 to 55 wt.% Mn range in an inert helium atmosphere. Burn rates between 2.5 and 11.2 mm·s–1 were recorded in open burn tests, whilst closed burn tests in glass tubes resulted in burn rates of 6.3 to 11.2 mm·s–1. Both X-ray diffraction analysis of the reaction products and thermodynamic simulations confirmed that MnO and Bi are the main reaction products, with unreacted Mn and Bi2O3 also being detected. This suggests that the dominant reaction for this composition is a simple thermite-type reaction.