The Burning Rate of Mn + MnCh and Mn + Sb2O3 Delay Compositions

摘要

Binary pyrotechnic systems containing Mn as fuel, with either MnO2 or So2O3 as the oxidants were investigated for time delay applications. The d_(50) particle sizes of the Mn fuel, the MnO2 and SD2O3 oxidant powders were 23.4, 8.25 and 0 92 μm 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 53 + 2 % TMD for the system Mn + MnO2 and 74 + 2 % TMD for the Mn + Sb2O3 system. With MnO2 as oxidant, the maximum adiabatic reaction temperature (>2000 K) coincided with a fuel content or 38.7 wt-% corresponding to the reaction: Mn + MnO2 → 2 MnO. The burning rate at this stoichiometric composition was ca. 7.4 mm s~(-1). Only one other composition, containing 45 wt-% Mn as fuel, burned reliably at ca. 5.0 mm s~(-1). EKVI thermodynamic modelling for Mn + Sb2O3 predicted two maxima in the adiabatic reaction temperature. The local maximum, at a manganese fuel content of la. 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. The burning rate increased linearly from 4.2 to 9.4 mm s~(-1) over the composition range 25-50 wt-% Mn.