ESI for JPyro, 26, 2007, p24
Ignition and Combustion of Aluminium in High Explosives
Attached are three SEM-images of the aluminium powder used in the study at different resolutions
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Selected Proccedings of the 5th Workshop on Pyrotechnic Combustion Mechanisms:
Ref: JPyro, Issue 26, 2007
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Thermal Stability of Hydrazinium Nitroformate (HNF) Assessed by Heat Generation Rate and Heat Generation and Mass Loss
Manfred A. Bohn
Abstract: HNF, hydrazinium nitroformate, H3NNH2 +·C(NO2)3−, is a water soluble salt. It has a positive oxygen balance of 13%, a much more positive enthalpy of formation than ammonium perchlorate (AP) and amuch higher heat of explosion than AP, 5579 J g−1 against 1972 J g−1. Additionally it has no chlorine and all the problems with hydrogen chloride formation can be avoided when used as oxidizer in rocket propellant formulations. All these advantages together could make HNF an oxidizer with better performance than AP. One inherent disadvantage may be the lesser thermal stability of HNF. Therefore an extensive investigation was performed on the thermo-chemical stability of HNF. Three sample lots of HNF have been investigated at ICT. They were provided by APP BV, The Netherlands. The thermal stability was determined by the following methods:
• autoignition temperature with 0.2 g at 5 °C min−1 heat rate in a Wood’s metal bath
• vacuum stability test (VST)
• heat generation rate as function of time and temperature
• mass loss as function of time and temperature
• adiabatic self heat rate.
Lots 2 and 3 have been characterised by heat generation rate at 60 °C, 65 °C, 70 °C and 75 °C and in short by mass loss. Lot 1 was extensively used for mass loss determinations in the temperature range 50 to 80 °C. HNF shows high heat generation rates. All curves from both methods indicate self accelerating behaviour. They have been described with autocatalytic reaction kinetic models. The Arrhenius parameters have been determined for lot 1 from mass loss data and for lots 2 and 3 from heat generation data. The activation energies for the intrinsic decomposition reaction are 166, 139 and 132 kJ mol−1 and for the autocatalyticreaction 159, 128 and 117 kJ mol−1 in the order lots 1, 2, 3. The kinetic data are compared and discussed. Data for lifetime at different temperatures are given in terms of the times to reach preset values of mass loss and energy loss.
Keywords: autocatalytic, kinetic, HNF
Ref: JPyro, Issue 26, 2007, pp65-94
(J26_65)
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Synthesis, Structural and Reactive Characterization of Miscellaneous Nanothermites
Denis Spitzer and Marc Comet
Abstract: In this paper, we report the elaboration and the characterization of several kinds of nanothermites made at the French German Research Institute of Saint‑Louis (ISL). Three types of materials are presented herein: tungsten trioxide based nanothermites obtained by physical mixing of this metallic oxide withaluminum nanoparticles; tungsten trioxide based nanothermites elaborated by coating WO3 nanoparticles with aluminum using a chemical process; and molybdenum oxide based nanothermites composed of AlxMoyOz nanostructured phases and aluminum nanoparticles. In the light of these examples, we have identified general trends concerning the structural and reactive behavior of the new materials.
Keywords: nanothermites, tungsten oxide, molybdenum oxide, aluminum coating
Ref: JPyro, Issue 26, 2007, pp60-64
(J26_60)
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Laser Diode Ignition of Pyrotechnic Mixtures: Experimental and Numerical Studies
Pr Philippe Gillard
Abstract: An experimental study of laser ignition of Zr/KClO4, Zr/PbCrO4, Fe/KClO4, Fe/KNO3, B/KClO4 and B/KNO3 mixtures is presented in this paper. The ignition system is composed of two lenses which focus the laser beam on the tablet. A sapphire porthole, juxtaposed with the pyrotechnic composition, protects the optical unit but causes losses of heat which result in an increase of the energy threshold.
This experimental set-up was used to determine the ignition sensitivity of five mixtures. A particular behaviour of B/KNO3 was observed. Experimental results pointed out an increase of the energy of ignition when the laser power grows. The other mixtures exhibit a conventional behaviour of the trend of ignition threshold E50 according to the power P of the laser beam: a continuous decrease of the value of E50 is observed when P is rising.
Some parameters linked to the experimental device also have a great influence. Among them the power density seems to be predominant but the thermal conductivity of the sapphire windows also plays an important role. It is possible to find an optimum value of the laser diameter, for a given power density. This experimental and parametric study have shown that, on such devices, it is possible to find optimal conditions of the ignition of various pyrotechnic mixtures.
A modelling, based on a progressive absorption of the laser beam inside a reactive pyrotechnic composition, was developed. It takes account of the energy exchanges between the ignition system and the pellet. Two interface parameters make it possible to optimize calculations. One relates to the heat transfer on the level of the porthole/tablet interface, the other relates to the laser absorption of energetic materials. By combining these two terms, it has been possible to corroborate the experimental thresholds on five different pyrotechnic mixtures.
To evaluate the interface parameters, whose implication in initiation is critical, several methods are exposed. One of them proposes a numerical calculation based on a random and automatic installation of the grains. The result gives Gaussian variables. This method enables simulation of the statistical tests of Bruceton and Langlie which are used in pyrotechnics.
The numerical results show that the sensitivity of the mixtures depends primarily on the propagation of heat towards the porthole and the interior of the tablet, as well as on the in-depth absorption of the laser in the pellet.
Keywords: Laser diode, ignition, pyrotechnic mixtures, numerical modelling
Ref: JPyro, Issue 26, 2007, pp53-59
(J26_53)
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Ignition And Burning Rate Characteristics Of Pyrolant Black Powder
Takuo Kuwahara
Keywords: Black powder, pyrolant, ignition delay time, burning rate
Ref: JPyro, Issue 26, 2007, pp47-52
(J26_47)
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