Mn+Sb₂O₃ Thermite/Intermetallic Delay Compositions

Abstract

Abstract The binary Mn+Sb 2 O 3 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: 3 Mn+Sb 2 O 3 →3 MnO+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 5 Mn+Sb 2 O 3 →3 MnO+2 MnSb, 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 Mn 2 Sb for fuel‐rich compositions. Burn rates were measured using delay elements assembled into commercial detonators. The d 50 particle sizes were 23.4 and 0.92 μm for the Mn fuel and Sb 2 O 3 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.