Condensed-phase species distributions about Al particles reacting in various oxidizers

Experimental results on the combustion of single, isolated aluminum particl es, laser ignited in quiescent environments consisting of pure N2O, CO2, CO and in mixtures of 21% O-2 / 79% N-2 and 21% O-2 / 79% Ar are reported. Co mbustion measurements consisted of photographic observations and electron p robe microanalysis (EPMA) of the condensed-phase product composition and ra dial distribution. Aluminum particles in O-2, CO2, and N2O atmospheres were found to burn with envelope flames. Of these oxidizers, the largest flame envelope, as determined by the condensed-product distribution, occurred for Al combustion in the O-2/Ar mixture, followed by Al combustion in the O-2/ N-2 mixture, the CO2 atmosphere, and the N2O atmosphere. Combustion in the CO atmosphere appeared to occur on (near) the particle surface with only a weak envelope reaction. Consistent with previous results in the literature, Al particle disruption was not observed in O-2/Ar environments, but was ob served in O-2/N-2 environments. Although speculated in the literature, the present work confirms the existence of aluminum nitrides (oxy-nitrides) in the fuel-rich region near the particle surface for nitrogen-containing oxid izers (i.e., O-2/N-2 and N2O). Equilibrium calculations indicate that near the surface, solid-phase AlN may exist to temperatures well above the melti ng temperature of aluminum oxide. Thus, its presence may affect the fragmen tation process. Finally, condensed-phase carbon (possibly in the form of al uminum carbide) was found throughout the surrounding gas-phase for CO combu stion. (C) 1999 by The Combustion Institute.