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 s1 over the
composition range 25 - 50 wt-% Mn.
