Modeling Ignition and Thermal Wave Progression in Binary Granular Pyrotechnic Compositions

Abstract

Oxidizer and fuel particles are the ingredients of classical pyrotechnics. Particle concentration, size, melting, evaporation, and decomposition of the particles, heat and mass transfer, reaction kinetics, and heat of reaction control the burning behavior of these mixtures. A hot‐spot approach models the reaction progress in three dimensions taking into consideration the particulate nature of pyrotechnic compositions. The governing reaction is assumed to be the oxidizer decomposition described by an Avrami‐Erofeev model. Predominantly, the distribution of the oxidizer and fuel particles and their size for various concentrations influence the burning rate beneath the reaction kinetic parameters. The computational results were compared with experimental progression rates and temperatures measured for an example system composed of various Al/CuO‐thermite mixtures with aluminum contents from 8 % to 70 %. The particle sizes were fixed to micrometer‐scale. The curve of progression rate calculations depending on the aluminium particle concentration and their distribution show the same shape as the experimental results.

Modelling of Al/MnO2 and Ti/MnO2 Thermite Mixtures

“…Besides the concentrations of metal and metal-oxide, the burning behaviour is controlled by the particle size, the melting, the evaporation and the decomposition of the particles, the heat of reaction, the heat and mass transfer and the reaction kinetics [6]. Also the distribution and the location of the single particles play an important role in the progression rate and temperature of overall reaction [1]. Numerous investigations on thermite reactions were done using different metals and metal oxides [7] studying burning rates [8,9], influence of particle size [10] and pressure [11,12].…”

“…The Hot-Spot model was already used for preliminary studies [21], describing particle ignition and propagation of reaction fronts in porous energetic materials [1,22,23]. In Ref.…”

“…In Ref. [1] the method was applied to the thermite reaction of aluminium with copper(II) oxide with varying fuel concentration and the results were compared to experimental data. It was shown that the Hot-Spot model is able to qualitatively reproduce the dependency of the progression rate on fuel concentration.…”

“…

In previous work a model was developed and introduced to describe the conversion of pyrotechnic mixtures taking in consideration its particulate character and solving the heat and the mass transfer coupled with reaction kinetics [1]. In this work the model was applied to thermite mixtures with manganese(IV) oxide as oxidizer and aluminium or titanium as fuel.

…”

Emission Spectroscopy of the Combustion Flame of Aluminium/Copper Oxide Thermite

“…The temperatures were determined by comparison of calculated with experimental spectra by a non-linear least squares fit. The final outcome will help to understand the involved processes in thermite combustion and to integrate the radiation processes in modelling of thermite mixtures [25][26][27] . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 2 Experimental Al/CuO (Toyal Europe: Alcan 400, 99.7 % min., Aluminium powder atomized; Alpha Aesar: Copper(II) oxide, 97 %, À325 mesh powder) particles were mixed for one hour in a tumbling mixer.…”