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

Experimental results on the combustion of single, isolated aluminum particles, 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. Combustion measurements consisted of photographic observations and electron probe microanalysis (EPMA) of the condensed-phase product composition and radial 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 observed 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 oxidizers (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 melting temperature of aluminum oxide. Thus, its presence may affect the fragmentation process. Finally, condensed-phase carbon (possibly in the form of aluminum carbide) was found throughout the surrounding gas-phase for CO combustion. (C) 1999 by The Combustion Institute.