Combustion Behaviors Resulting from Bimodal Aluminum Size Distributions in Thermites

Burn time of aluminum nanoparticles: Strong effect of the heating rate and melt-dispersion mechanism

“…trast to speeds on the order of m/s for micron scale Al particles [15]) can be obtained by complete or almost complete burning of Al nanoparticles. Indeed, unreacted Al serves as a heat absorber and is a deadweight, similar to alumina shell.…”

“…Unfortunately, it is difficult to increase the heating rate in the experimental setup in [1] or decrease it in the setup of [3,4] to answer this question precisely. For an approximate estimate, we will use experimental data on flame propagation in Al and molybdenum trioxide composites for bimodal Al particle distributions [15] when nanoparticles were mixed with micron scale particles. Based on slow flame rate, the particles with diameters 4 μm and 20 μm alone used in [15] do not react according to the melt dispersion mechanism.…”

“…R/δ = (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). This means that a major portion of nanoparticles did not satisfy the criterion for complete melting of Al before oxide fracture R/δ < 19 [6,7].…”

The effect of Si–Bi2O3 on the ignition of the Al–CuO thermite

“…The discussion presented above amply demonstrates that nano-sized aluminium powder imparts improved ignition sensitivity and greatly enhances the energy release rate of thermites. In fact, Moore et al [24] showed that even a partial substitution ( 20 wt %) of micron-sized fuel in the Al + MoO 3 thermite is sufficient to reduce the ignition delay times by up to two orders of magnitude and to dramatically increase the combustion velocity. This communication explores further sensitization of the Al + CuO thermite reaction [25] by the fastburning Si + Bi 2 O 3 pyrotechnic composition [26,27].…”

Characterizing pyrotechnic igniter output with high-speed schlieren imaging

“…The thermally ignited pyrotechnic powder near the bridgewire transitions to a sustained combustion front that consumes the remaining material and releases exothermic energy into the surrounding environment [3]. Fundamental studies of the ignition and combustion characteristics of pyrotechnics [4][5][6][7], thermites [8,9], and intermetallics [10] have been conducted by numerous researchers where the material parameters of particle size, bed porosity, and mixture composition have been explored. In pyrotechnic EED development, the interplay between the igniter design aspects and the combustion behavior directly impact the energy released in the surrounding environment.…”