Radial combustion propagation in iron(III) oxide/aluminum thermite mixtures

The self-sustained thermite reaction between iron oxide (Fe2O3) and aluminum is a classical source of energy. In this work the radial combustion propagation on thin circular samples of stoichiometric and over aluminized Fe2O3/Al thermite mixtures is studied. The radial geometry allows an easy detection of sample heterogeneities and the observation of the combustion behavior in their vicinity. The influence of factors like reactant mixtures stoichiometry, samples green density and system geometry on the rate of propagation of the combustion front is analyzed. The radial combustion front profiles are registered by digital video-crono-photography. Combustion thermograms are obtained for two sample radii. Theoretical calculations, based on the impurity levels reported by the reactants manufacturers and on the thermite reaction stoichiometry, were used to define the stoichiometric mixture with unitary equivalence ratio (E. R.). However, it was found from the experimental results that the excess of aluminum only starts for E. R. values between 1.12 and 1.27. This was explained by the further oxidation of aluminum during storage and/or by the reaction incompleteness. In the range studied, the combustion rates of the thermite mixtures did not show any significant dependence on the green density. Combustion rates obtained in this work were slightly higher than those obtained in an earlier work for long square channel geometry. A considerable dispersion of temperature values was observed and attributed to thermocouples sensitivity to micro-scale variations.