Underwater Explosive Behaviour of Compositions Containing Nanometric Aluminium Powder
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Underwater Explosive Behaviour of Compositions Containing Nanometric Aluminium Powder Leslie R Bates Modelling and Explosives Applications, QinetiQ, Dstl Fort Halstead, Sevenoaks, Kent, TN14 7BP, UK ABSTRACT Results from research aimed towards the understanding of the effect that ultrafine aluminium powder has on the explosive performance of underwater explosives are presented. A series of aluminised explosive compositions using a commercially available nanometric aluminium powder (Alex) have been prepared and quantified underwater. The results have been compared with the corresponding compositions using conventional aluminium powders. An enhancement in explosive properties can be seen. The effect is not universal but can be related to the reaction zone length, and time, of the base explosive being sufficiently long for the oxidation of the aluminium, with its substantial energy release, to take place in or close to the reaction zone. INTRODUCTION The addition of aluminium powder as a fuel to underwater explosive compositions to increase their shock and bubble energy is well known, and increases of 20% in shock wave energy and 60% in bubble energy over the non-aluminised explosive material are generally realised [1,2]. The burning time of a particle of fuel is proportional to the square of its radius so for very small particles this burn time becomes very short indeed and approaches that of the reaction time for the detonation of an explosive. Typical timescales of pertinent detonation parameters and the behaviour of aluminium particles is given by Milne [3] in Figure 1. Thus the incorporation of nanometric aluminium into explosives could well have a profound effect on the detonics of the system and therefore on the explosive performance. A theoretical study of particle combustion in explosive systems by Milne [3] indicated that an important factor to enable the full theoretical energy of aluminium combustion to be released was the reaction zone length and time of the base explosive. An energy deficit was forecast with nanometric aluminium and any explosive with a very short reaction zone length. The lower limit of aluminium particle size achieved by convention atomisation and physical attrition means is about 1-3 microns. Aluminium powder of particle size in the range 80-100nm can be made by vapour condensation techniques and is now commercially available. One such powder is marketed under the name of “Alex” and is supplied by the Argonide Corporation [4]. In this study the underwater explosion behaviour of three explosive systems were investigated; nitromethane/Alex, RDX/Alex and RDX/Polyglycidylnitrate/Alex. EXPERIMENTAL DETAILS The underwater explosive performance evaluation of the compositions in this study was carried out at the QinetiQ Explosives and Shock Test Facility, St. Thomas’ Head, Weston-Super-
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Mare, UK. This sea-based site can provide free field conditions for the quantification of shock wave and bubble energies for charge masses up to 9kg. The tidal conditions allow experiments t
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