Aluminum particle ignition in mixed environments

An experimental study of aluminum particle ignition in different oxidizing environments is reported. Aluminum particles in the μm size range are ignited by a CO₂ laser in air, water vapor, carbon dioxide and mixtures of thereof. The particles are passing through the laser beam of fixed diameter at different velocities enabling experiments at varied heating rates and thus enabling one to determine the ignition kinetics. Ignition and combustion events are distinguished optically. Experiments are interpreted considering heat balance for a metal particle in a cold oxidizing environment. Experiments and estimates both show that achievement of a vapor phase flame around single Al particle is difficult in water vapor, when the adiabatic flame temperature is substantially lower than that in oxygenated environments. However, if the flame is established, the rate of reaction of aluminum in water is higher than that in other environments. Approximate Arrhenius-type descriptions for aluminum ignition in different oxidizing environments are proposed suitable for processes involving high heating rates of the order of 10⁶-10⁷ K/s.