Mn+Sb2O3 thermite/intermetallic delay compositions

Abstract

The binary Mn + Sb2O3 pyrotechnic composition was investigated for mining detonator time delay applications. EKVI thermodynamic modelling predicted two maxima in the adiabatic reaction temperature. The local maximum, at a manganese fuel content of ca. 36 wt-%, corresponds to a pure thermite-type redox reaction: 3Mn + Sb2O3  3MnO + 2Sb. The overall maximum in the adiabatic reaction temperature (ca. 1640 K), at the fuel-rich composition of 49 wt-% Mn, is consistent with the reaction 5Mn + Sb2O3  3MnO + 2MnSb, i.e. a combination of the standard thermite with an additional exothermic intermetallic reaction. XRD analysis of combustion residues confirmed the formation of MnSb and Mn2Sb for fuel-rich compositions. Burn rates were measured using delay elements assembled into commercial detonators. The d50 particle sizes were 23.4 and 0.92 m for the Mn fuel and Sb2O3 oxidant powders respectively. The delay elements comprised rolled lead tubes with a length of 44 mm and an outer diameter of 6.4 mm. The rolling action compacted the pyrotechnic compositions to 74  2 % theoretical maximum density. The burning rate increased linearly from 4.2 to 9.4 mm s1 over the composition range 25 - 50 wt-% Mn.