Chemical time delay detonators are used to control blasting operations in mines and quarries. Slow burning Si-BaSO4 pyrotechnic delay compositions are employed for long time delays. However, soluble barium compounds may pose environmental and health risks. Hence inexpensive anhydrous calcium sulfate was investigated as an alternative "green" oxidant. EKVI simulations indicated that stoichiometry corresponds to a composition that contains less than 30 wt. % Si. However combustion was only supported in the range of 30-70 wt. % Si. In this range the bomb calorimeter data and burn tests indicate that the reaction rate and energy output decrease with increasing silicon content. The measured burn rates in rigid aluminium elements ranged from 6.9 to 12.5 mm s 1. The reaction product was a complex mixture that contained crystalline phases in addition to an amorphous calcium containing silicate phase. A reaction mechanism consistent with these observations is proposed.
The burning rates of a slow reacting Mn + Sb 2 O 3 and a fast reacting Si + Pb 3 O 4 time delay composition, filled into lead tubes, were measured with an infrared camera, with two thermocouples and in the form of a fully assembled detonator. The infrared camera method returned values that were on average about 12 % lower than those recorded for the detonators. The temperature profiles measured for the slow burning elements were fully developed, whereas those obtained for the fast burning Si + Pb 3 O 4 elements were not. A numerical model was developed to simulate the Mn + Sb 2 O 3 system. Kinetic parameters were determined by least square fits to the recorded surface temperature profiles. The model made it possible to determine the effect of various property variations on the burning rate. The thermal conductivity of the delay composition was found to have the smallest impact and the heat of reaction the largest effect.
The feasibility of aluminium or magnalium filled fluoropolymer Viton B as an open-burn time delay was investigated. Film samples with a thickness of 245 21 m. were prepared via a slurry casting process. Fuel filler content was varied from 20 to 60 wt.%. The films retained the elastic properties of the parent polymer except that the elongation at break decreased rapidly with increasing filler content.Sensitivity tests showed that the films were insensitive to ignition by friction and impact. EKVI thermodynamic simulations showed that, for both systems, the maximum energy output is ca. 8.3 MJ kg 1 . Energy measurements indicated that the maximum energy output occurred in the range 30 to 40 wt.%. Maximum burn rates of 82 mm s 1 and 40 mm s 1 were achieved using a magnalium and flake aluminium as fuels respectively.
Abstract:The binary Mn + Sb 2 O 3 pyrotechnic composition was investigated for mining detonator time delay applications. EKVI thermodynamic modelling predicted two maxima in the adiabatic reaction temperature. The local maximum, at a manganese fuel content of ca. 36 wt-%, corresponds to a pure thermite-type redox reaction: 3Mn + Sb 2 O 3 3MnO + 2Sb. The overall maximum in the adiabatic reaction temperature (ca. 1640 K), at the fuel-rich composition of 49 wt-% Mn, is consistent with the reaction 5Mn + Sb 2 O 3 3MnO + 2MnSb, i.e. a combination of the standard thermite with an additional exothermic intermetallic reaction. XRD analysis of combustion residues confirmed the formation of MnSb and Mn 2 Sb for fuel-rich compositions. Burn rates were measured using delay elements assembled into commercial detonators. The d 50 particle sizes were 23.4 and 0.92 m for the Mn fuel and Sb 2 O 3 oxidant powders respectively. The delay elements comprised rolled lead tubes with a length of 44 mm and an outer diameter of 6.4 mm. The rolling action compacted the pyrotechnic compositions to 74 2 % theoretical maximum density. The burning rate increased linearly from 4.2 to 9.4 mm s 1 over the composition range 25 -50 wt-% Mn.
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-BaSO 4 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.
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