Anomalous dependence of the combustion rate of thermite mixtures on the pressure

Thermite type reactions are usually used when high quantities of heat should safely be produced with low gas release. Stoichiometric samples of aluminium, magnesium and titanium particles in mm-scale were mixed with iron(III) oxide and filled into small test tubes maintaining a constant bulk density. The metals were chosen regarding their heat release, melting and boiling point, the latter also important for the metal oxides. The samples were burnt in a window bomb pressurised from 0.1 to 13 MPa with nitrogen. The reaction was observed using a colour high-speed camera equipped with a macro object lens and different fast scanning emission spectrometers in UV/Vis and NIR to determine burning velocity, emitting species and reaction temperatures. The residues were analysed using scanning electron microscopy (SEM) including energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The samples burnt in a reproducible way at a linear regression rate. A strong influence of pressure on the burning velocity and reaction zone temperatures was observed. The burning velocity varied by a factor of 3 forming a maximum at a certain pressure that is characteristic to the type of metal. In correlation, temperatures varied by several hundred Kelvin. Results were discussed regarding the decomposition, melting and boiling behaviour also including thermodynamic equilibrium calculations resulting in a qualitative two-step model of interacting and reacting droplets.

Section: Introductionmentioning

confidence: 99%

Thermite Type Reactions of Different Metals with Iron‐Oxide and the Influence of Pressure

Weiser

Roth

Raab

et al. 2010

“…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]. However, the physico-chemical mechanisms of thermite-type reactions are still far from being completely understood and we are far away from predicting the reaction behaviour of new pyrotechnic mixtures.…”

Section: Introductionmentioning

confidence: 99%

Modelling of Al/MnO₂ and Ti/MnO₂ Thermite Mixtures

Knapp

Eisenreich

Kelzenberg

et al. 2019

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. The modelling results of burning rate dependent of fuel‐oxidizer ratio were compared with results from experiments. For the modelling process, the educts were characterized by determining particle size and distribution and chemical reaction kinetics parameters. Other parameters were taken from literature. The modelling results are in good agreement with the experimental ones. It seems that the made physical and chemical assumptions are the main factors to describe the shape of burning rate profile in thermite combustion and the negligence are not influential.

“…Currently, numerous investigations on thermite reactions are done using different metals and metal oxides [8] studying burning rates [9], influence of particle size [10] and pressure [11,12]. However, the physico-chemical mechanisms of thermite type reactions are still far from being completely understood.…”

Section: Introductionmentioning

confidence: 99%

Modeling Ignition and Thermal Wave Progression in Binary Granular Pyrotechnic Compositions

Knapp

Weiser

Kelzenberg

et al. 2014

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.