The development of a new non-metallic explosives initiator
Bezuidenhout, Hendrik Cornelius
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Explosives are used to achieve certain functions in diverse environments, including mining, civil construction, military operations, and demolition. Irrespective of the application, the basic principle of augmentation of energy applies. Energy in the form of heat and shock is released by an initiator. This energy is taken up by an intermediary charge, which in turn propagates to the main explosive charge. Ultimately the energy released from the main explosive charge performs the functions. Initiating systems make use of this exact principle within their own boundaries of confinement. The rate at which this energy transfer takes place as well as the magnitude of augmentation is to a great extent influenced by parameters such as the type of confinement, chemical composition and density of the explosives, as well as other environmental conditions. Traditionally lead azide has been used as the primary explosive component in an initiating system. Pressure from international environmental agencies has discouraged the use of heavy metals in commercial products. Nano-porous silicon has been used together with an oxidiser to form an explosive mixture. The literature has shown that nano-porous silicon-based explosive formulations are sensitive enough to pick up from the energy released by the pyrotechnic composition. The reaction of such nano-porous silicon explosive compositions changes from a deflagration to a detonation. However, their ability to initiate the base charge of an initiating system has not yet been demonstrated. A nano-porous silicon/nitriminotetrazole-based explosive system was developed and characterised. A relative reactivity concept was developed and successfully used to further characterise the new nano-porous silicon explosive. The lead azide primary explosive replacement has been shown to be sensitive enough to pick up from the heat output generated by the delay composition and strong enough to reliably initiate the base charge explosive. The performance of the base charge explosive is primarily a function of its density and the confinement it is used in. An explosive system was developed whereby the base explosive was coated with a polymer to give it compressible characteristics. A ballistic ball indentation evaluation method was developed and effectively applied to characterise explosive performance behaviour under various conditions, including density and confinement. Explosive pellets, pressed separately and at a higher density, have been shown to increase performance compared with explosives consolidated inside an aluminium casing.