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: 3Mn + Sb 2 O 3  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 + Sb 2 O 3  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 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 m 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.

Measurement and Modelling of Pyrotechnic Time Delay Burning Rates: Method and Model Development

“…The thermochemistry for the reaction of Mn with Sb 2 O 3 was previously reported [13]. The normal redox reaction: 3Mn + Sb 2 O 3 !3MnO + 2Sb dominates in fuel-lean mixtures.…”

Review of Gasless Pyrotechnic Time Delays

“…Manganese/antimony trioxide. EKVI thermodynamic modelling predicted two maxima in the adiabatic reaction temperature for the binary Mn/Sb 2 O 3 pyrotechnic system [90].…”

“…Dugam et al [74] investigated the effect of particle size distributions and found higher packing densities for wider distributions of oxidant particle sizes and lower packing densities when the fuel and oxidant particles have similar sizes. Montgomery et al [90] investigated the effect of particle packing through variations in fuel to oxidant particle size ratios. The particle packing was found to be unaffected by the volumetric ratio of the fuel to oxidant particles.…”

“…These indirect measurements are, however, also influenced by other parameter variations. Montgomery, et al [90] used scanning electron microscopy to qualitatively probe the degree mixing. However, this only provides a two-dimensional representation of the mixing.…”

“…Experimental burning rates for the system Mn/Sb 2 O 3 as a function of fuel content in rolled lead tubes[90]. The d 50 values were 23.4 mm and 0.92 mm for the Mn fuel and the Sb 2 O 3 oxidant respectively.…”