Archive for March 2008

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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Pyrotechnic Chemistry Course – LiuYang

A course has been provisionally arranged in Hunan.  Please contact Andrew tang (Details below) for more information 

Venue : Tian Cheng Pyrotechnics Laboratory,Lihua Village, Yanxi Town, Liuyang City, Hunan,
Cost : To be determined.
Contact : Mr. Andrew Tang (email:atang@tcpyrolab.org)
Fax: 86-731-394 0679
Tel: 86-731- 394 1206

JPyro – Issue 26, Winter 2006 – Contents

Full Papers:

Selected Proccedings of the 5th Workshop on Pyrotechnic Combustion Mechanisms:

j26-cov.JPG


Ref: JPyro, Issue 26, 2007
(J26)

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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

Abstract: Composite propellants contain binder as fuel which connects oxidizer particles and metals. The burning rate of a propellant is affected by the concentration and type of binder. Pyrolant is mixed with oxidizer particles and metal particles. Pyrolant does not contain binder, so burns smoothly. The burning rate of black powder (BP) which is a kind of pyrolant is higher than that of AP composite propellant. The shorter the reaction time in the gas phase near the burning surface of black powder becomes, the higher the burning rate becomes. The burning rate of BP is inversely proportional to the ignition delay time.

Keywords: Black powder, pyrolant, ignition delay time, burning rate


Ref: JPyro, Issue 26, 2007, pp47-52
(J26_47)

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Ignition and Combustion of Aluminium in High Explosives

Arno Hahma

Abstract: Ignition and combustion properties of aluminium powder up to 250 kbar pressure were successfully determined. Hydrodynamic modelling combined with parametrized reaction profiles was used to match the experimental metal plate profiles to calculated values and the metal reactivity was determined from the parameters thus obtained. The reaction profiles over a wide range of specific volumes and pressures were obtained. Aluminium ignited only if the detonation temperature was higher than 2300 K and the aluminium oxide was decomposed; even a strong shock wave was not able to clean the aluminium surface to promote ignition at lower temperatures. Aluminium reactivity at the Chapman–Jouguet plane (C-J plane) was concluded to be insignificant in all cases studied. A maximum of only 17 % reactivity by an expansion ratio of 1 : 50 was reached. The aluminium combustion could be best described with a power law Apn and the pressure exponent of aluminium was found to be slightly positive: +0.33. Nitrogen rich explosives were concluded to be necessary to convert Al energy effectively to mechanical work and to unambiguously measure the Al reactivity.

Keywords: Aluminium, Chapman–Jouguet plane, ignition, combustion, hydrodynamic modelling


Ref: JPyro, Issue 26, 2007, pp24-46
(J26_24)

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5th Workshop on Pyrotechnic Combustion Mechanisms, held October 6th 2007 in Beane, France

Ernst-Christian Kocha and Rutger Webbb

For the fifth time the “Workshop on Pyrotechnic Combustion Mechanisms” was held and organized in conjunction with the International Pyrotechnics Seminar. This time it was the 34th IPS Seminar in conjunction with EUROPYRO 2007, in Beaune, France.

This workshop had a total of 21 participants, of which 4 were from France, 4 from Germany, 4 from USA, 3 from the UK, 2 from The Netherlands, 1 from South Africa, 1 from Japan, 1 from Russia, and 1 from Finland.

This event received very positive feedback from both participants and presenters. Papers based on the following presentations have already, or are expected to be published elsewhere.

• Volker Weiser, Fraunhofer ICT, Germany, Modeling Spectral Emission and Radiation Intensity of Pyrotechnic Reactions

• Alexander Dologoborodov, Semenov Institute Moscow, Russia, Mechanoactivated Energetic Composites on the Base of Metal – Oxidizer Mixtures

• Selena Burn, BAE Systems, UK, Personal Protective Equipment

The next workshop on pyrotechnic combustion mechanisms will be held on July 13 2008 in Fort Collins Colorado in conjunction to the 35th International Pyrotechnics Seminar. The topics then will focus on safety and sensitivity of pyrotechnics. For further information on that event please refer to www.pyroworkshop.net


Ref: JPyro, Issue 26, 2007, pp23-23
(J26_23)

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Atmospheric Flight Dynamic Simulation Modeling Of Spin-Stabilized Projectiles And Small Bullets With Constant Aerodynamic Coefficients

Dimitrios N. Gkritzapis, EliasE. Panagiotopoulos, Dionissios P.Margarisb and Dimitrios G.Papanikas

Abstract: A full six degrees of freedom (6-DOF) simulation flight dynamics model is applied for the accurate prediction of short and long range trajectories of high and low spin-stabilized projectiles and small bullets via atmospheric flight to final impact point. The projectile is assumed to be both rigid (nonflexible) and rotationally symmetric about its spin axis launched at low and high pitch angles. The projectile maneuvering motion depends on the most significant forces and moments, in addition to wind, gravity and Magnus effects. The computational flight analysis is based on appropriate constant mean values of the aerodynamic projectile coefficients taken from an official tabulated database. The newer ICAO atmospheric model simulates the height distributions of density, pressure and temperature properties of the air. Static stability, also called gyroscopic stability, is examined as a necessary condition for stable flight motion in order to determine the sufficient initial spinning projectile rotation. The efficiency of the method developed gives satisfactory results compared with published data of verified experiments and computational codes on atmospheric dynamics model flight analysis.

Keywords: Trajectory dynamics simulation, constant aerodynamic analysis, high and low pitch angles, Magnus effects, symmetric projectiles, static stability criteria


Ref: JPyro, Issue 26, 2007, pp15-22
(J26_15)

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