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A miniature rocket device integrating nanothermite and RDX is presented for shock initiation of high explosive application. This Ø 2.5 mm device consists in several assembled and screwed parts: a pyroMEMS chip with a Al/CuO multilayers on it to ignite within less than 100 μs a few milligrams of nanothermite, which reacts violently and ignites within 150 μs a RDX charge compacted in the closed combustion chamber. The gases generated by the RDX combustion rapidly expand, cut and propel a Ø 2.5 mm by 1 mm thick stainless steel flyer in the barrel. After the presentation of the rocket design, fabrication and assembly, by measuring the pressure‐time evolution in the chamber we demonstrate the advantage to ignite the RDX with Al/Bi2O3 nanothermite to optimize the pressure impulse. We show that the stainless steel flyer of 40 mg is properly cut and propelled at velocities calculated from 665 to 1083 m s−1 as a function of the RDX extent of compaction and ignition charge. As expected, the average flyer velocity increases with the mass of loaded RDX and flyer's shear thickness. We finally prove that the impact of the flyer can initiate directly in detonation a RDX explosive, which is very promising to remove primary explosives in detonator.

[a] 1I ntroductionAlumino-thermite materials represent an interesting class of energetic substances notably because of their high energy densities, adiabatic flame temperature, and when nanosized, high reaction rates. Alumino-thermite is an oxidation-reduction reaction involving am etal (fuel) and am etallic oxide (or possibly an on-metallic oxide) that forms as table product after reaction.Thermite materials have been actively investigated for aw ide range of potential applications including railroad welding, materials processing to form refractory materials, additives in propellants, explosives and pyrotechnics [1][2][3], and more recently also for micro initiation [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20],e nvironmentally clean primers, and in situ welding [21].Among the numerous possible exothermic metal/oxide pairs listed in the literature [22],t he most investigated ones mix Al with MoO 3 ,C uO, Bi 2 O 3 ,F e 2 O 3 ,M nO 2 ,W O 3 ,a nd I 2 O 5 .F or the last two decades most of the research efforts aimed at reducing metal and oxide components size, improving their intimacy,t oi ncrease the reaction rate and decrease the ignition delay while improving safety.More recently,t hermite materials were also considered to produce gas species or pressure bursts, opening new potential fields of application such as pressure mediated molecular delivery [23,24],b iological agent inactivation [25][26][27],h ydrogen production [28,29],o rp ropulsion systems [7][8][9].Af ew teams demonstrated experimentally that Al/Bi 2 O 3 and, to al esser extent, Al/I 2 O 5 mixtures generate the highest pressure pulses [27,30,31] in comparison with other thermites. Martirosyan [31] considered that the reaction product (bismuth or iodine) boils at at emperature of 1560 8Ca nd 184 8C, respectively,w hich is lower than the maximum reaction temperature:t herefore causing bismuth or iodine evaporation with subsequent increase of the released gas pressure.For some thermites, such as Al/CuO, experiments using time-resolved mass spectrometry have measured significant O 2 release under rapid heating [32,33].T he formation of gaseous intermediates and their contribution to the pressurization may suggest why as ystem such as Al/MoO 3 , which is thermodynamically predicted to produce approximately only ap ercent of the gas that Al/CuO or Al/Bi 2 O 3 does, reacts rapidly and generates pressure as many other thermites.Despite these experimental research investigations, the effects of thermite composition, packing density together with its environmental conditions on the gas production (type and repartition of produced species and rate of gas release) need to be studied and understood in greater detail. On the theoretical side, af irst attempt to simulate Abstract:T he paper proposes an ew theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to predict the total pressure and the partial p...

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The back cover picture shows: a Ø 2.5 mm miniature electric detonator for impact ignition of high secondary explosives without using primary high explosive. An exploded view of the miniature device is illustrated on the top image. The ignition is realized with only 80 μJ, thanks to a pyroMEMS chip (4×2 mm2) consisting in a thin Al/CuO nanothermite deposited on a micro electro‐thermal heater. On the left part of the image, two pyroMEMS are shown. Once ignited, the thin nanothermite film reacts, produces an intense emission of light and emits hot particles over several millimeters. The so called flame thereby ignites a ring of 17 mg of packed Al/Bi2O3 nanothermite in a fraction of ms which then ignites within 150 μs, 75 mg of RDX contained in the combustion chamber (Ø 2.5mm × 1.2 cm). The high energetic gases accelerate a metallic flyer of 40 mg at 600 to 1000 m.s−1 to impact the secondary explosives to ignite. Shock to detonation transitions have been successful demonstrated with a success rate of 80%. The innovation and interest of such miniature electric detonators lie in the possibility to ignite high secondary explosives from only 80 μJ of electrical energy without the use of primary explosive. More details are discussed in the article by Ludovic Glavier et al. on pp. 308 ff.

The paper is a theoretical exploration of complex Al/CuO thermite combustion processes, using a zero-dimensional (0D) model which integrates both condensed phase and gas phase reactions, and considers all thermodynamic stable molecular or atomic species identified during the Al + CuO reaction. We found that the particle size mainly influences the reaction kinetics and pressure development. Thermite with nano-sized particles (nanothermites) burns ~10 times faster than the same thermite with micron-sized particles (microthermites). This is due to the fact that the thermite reaction occurs mainly in condensed phase, i. e. in the melted Al phase, as all gaseous oxygens released by the CuO decomposition are spontaneously absorbed on the huge specific surface area of metallic Al. As a consequence, the pressure development in nanothermites follows the thermite chemical reaction, the gas phase is mostly composed of a metal vapor (mostly Cu and Al), Al suboxides, but is free of molecular oxygen. In contrast, when dealing with microthermites, an oxygen pressure peak occurs prior to the thermite reaction due to the gaseous O 2 released by the early CuO decomposition, that cannot be absorbed on the Al particles surface in real time. The powder stoichiometry greatly impacts the final pressure. Al lean thermites generate a higher final pressure (× 3) than stoichiometric and Al rich mixtures, due to unreacted gaseous oxygen which remains in the gas phase after the full consumption of the metallic Al.