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

Abstract

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.

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

“…This is confirmed by emission spectra showing band systems of intermediate products and is shown e. g. in Ref. [22]. In the case of aluminium/copper(II) oxide thermite reaction, research has been reported in [23] and [24] also focused on nano-thermites and the determination of relative intensities and temperature determination by grey body radiation.…”

In-situ measurements of the onset of bulk exothermicity in shock initiation of reactive powder mixtures

“…Unlike molecular explosives, which have a pressure-dependent burning speed r $ p n (n of order 1 or 2), 10,65 the SHS, thermite, and intermetallic compositions that have been studied appear to have burning speeds that are relatively independent of pressure due to the low fraction of gas-phase products. 11,12 The pressure-independence of the burning speed also results in bulk reaction times that are independent of initiating shock strength in contrast to the strong pressure dependence of explosive shock-to-detonation transition times (see Ref. 66 for instance).…”

Modelling of Al/MnO2 and Ti/MnO2 Thermite Mixtures

“…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.…”