Combustion of Mechanically Alloyed Aluminum-Magnesium Powders in Steam

Mechanically alloyed Al-Mg powders with the mole fraction of Al varied from 0.47 to 0.9 were burned at atmospheric pressure in water vapor. The powders were carried by nitrogen through the center of a hydrogen-oxygen diffusion flame. The particles ignited in the steam at approximately 2500 K, generated as the hydrogen-oxygen flame product. Filtered photomultiplier tubes were used to capture the optical emission traces of individual particles as they burned. It was assumed that the measured durations of individual emission pulses are representative of individual particle burn times. Distributions of the burn times were obtained for each powder and correlated with respective particle size distributions to relate particle burn times with their sizes. Color temperatures corresponding to the particle emission signals were also obtained. It was observed that the burn times measured for alloys were more close to those of pure Al than Mg; for particles smaller than 2-3 μm, burn times for the alloys were shorter than for pure metal particles. The effect was strongest for the alloy with 50wt-% of Mg (Al₀.47 Mg₀.54). Approximately, burn times, τ, as a function of particle size, d, could be estimated using a τdⁿ law, where n increased from 0.72 to 1.05 as the mole fraction of Mg increased from 0.1 to 0.53. The particle flame temperatures varied between 2500 and 3100 K for all alloys except for Al₀.7Mg₀.3, for which the temperatures were somewhat lower. The measured flame temperatures were reasonably close to the adiabatic flame temperatures calculated for combustion of mixed elemental Al and Mg in steam.