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

Abstract

AbstractThermite 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 μm‐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.