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ISSN Imprimir: 2150-766X
ISSN On-line: 2150-7678
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AEROSOL EMISSION MEASUREMENTS OF ROCKET MOTORS FROM CONTAINED OPEN BURN EVENTS
RESUMO
Aerosol concentrations were measured and samples collected from contained burn tests carried out on two types of rocket motors, the NIKE M88 and the Improved HAWK. Each rocket motor contains 750 pounds of double base type propellant, and 605 pounds of composite type propellant, respectively. The tests were carried out in a sealed underground test chamber of approximate volume 4644 m3. Aerosol emissions were sampled using an aerosol instrument outside of the burn chamber, after each rocket motor burn, by drawing aerosol-laden gas through the barrier into two parallel sampling systems. One system (impactor) collects aerosol samples from 0.1 to 10 μm in aerodynamic diameter and measures their mass concentrations and size distributions (μg/m3) in real time. The other system (streaker) collects three size fractions, > 10 μm, 2.5−10 μm, and < 2.5 μm with the latter two size fractions collected on rotating substrates thereby providing a time resolved series of samples. The streaker samples are analyzed using Proton-Induced X-ray Emission (PIXE) Spectroscopy to determine the aerosol elemental composition for elements of atomic number greater then Sodium (Z=11). The aerosol emissions from the burn tests were compared with samples, analyzed by PIXE, of background materials (shotcrete, concrete, aggregate, and tuff) taken from the chamber prior to the tests. The background materials are dominated by Calcium, Aluminum, Silicon, Potassium, Titanium, Chromium, Manganese, and Iron. In contrast, the elemental concentrations in the aerosols from the NIKE test are dominated by Sb and Pb, that are used as moderators in the propellant. Cu, probably be from the linear shaped charges used to initiate the explosive, is also present in the test samples. Aerosols were mostly near 1 μm in size. For the HAWK test, the aerosol is dominated by Al, which occurs in the propellant as metallic Al and is converted to Al2O3 upon combustion. Aerosols were initially mostly larger than 1 μm shifting to a bimodal size distribution with submicron particles and coarse particles (> 2.5 μm) predominating at the expense of small super-micron sized particles. In both tests we see a complex behavior of the aerosol size distribution with time as competing tendencies of aerosol growth by coagulation and settling out of larger particles occur.