Combustion of aluminum powder using CO2 laser in O2/CO2 atmosphere under different pressure conditions

The processes of ignition and combustion of aluminum (Al) under different pressure conditions have received widespread attention. In the present work, experiments were performed in a mixed O2/CO2 atmosphere and at five different pressures (1 atm, 5 atm, 9 atm, 13 atm and 17 atm) to study the ignition and combustion of aluminum. The microstructure and burning rate of the condensed phase products were determined using scanning electron microscopy and inductively coupled plasma spectrometer. The results showed that, with the increase in pressure, the ignition delay time of the sample shortened, while the combustion temperature, heat release rate, maximum intensity of the emission spectrum and burnout rate gradually increased. Experiments showed that at the pressure of 17 atm, the minimum ignition delay time (36 ms) achieved. At the same time, the combustion temperature and maximum burnout rate arrived at their maximum, which are 1855 °C and 99.53%, respectively. However, under high- and low-pressure conditions, there were two distinct reaction mechanisms. One was the melt-dispersion reaction (rupture of the oxide layer), which occurred under high pressure, while the other was the diffusion reaction (molecular diffusion), which took place under low pressure. In addition, physical models of the Al sample under high- and low-pressure conditions were established. The ignition temperature of Al in O2/CO2 atmosphere at 1 atm was about 930 °C. The spatial distributions of Al and AlO radicals under different pressures were found to be similar. The radicals were more concentrated on the surface of the sample, while free radicals diffused into the gas phase and reacted only under high temperature.