Atomic insight into the combustion behavior of aluminum nanoparticles under mixed atmosphere of H2O, CO2 and O2

The reaction processes between aluminum particles and H2O/CO2/O2 mixture at high temperatures are not clear. The reaction systems of H2O/Al, CO2/Al, O2/Al and mixed H2O/CO2/O2/Al were established, and molecular dynamics simulations of the ignition combustion process of Al nanoparticles in different systems were carried out under the reactive force field (ReaxFF). The effect of O/Al ratio on the reaction path with oxidizing molecules during particle combustion was investigated by varying the particle size and the number of oxidizing molecules. Under the condition of a variety of gas oxidizing molecules, the combustion of aluminum is still a process dominated by the diffusion of O atoms. The O atoms in the external oxidizing gas react with the surface of Al and enter the oxide layer, forcing the O atoms in the initial oxide layer to move inward and react with the internal aluminum, and eventually lead to the oxidation of the entire Al particles. This process is independent of the type of gas molecules. The combustion of Al in CO2 produces CO molecules, the number of which first increases and then decreases due to the continued reaction to produce C2n+2Aln, while the reaction of Al with H2O produces a large number of H and H2 molecules. However, when multiple components are present at the same time, these intermediate components react with other molecules, causing a change in the reaction path between the com-ponents and Al. In the H2O/CO2/O2/Al system, there are more oxygen atoms relative to the number of molecules, so that more H atoms will leave the Al and form HmAln with the free Al atoms, while more C atoms will be adsorbed on the Al surface, preventing them from leaving the Al. Comparing the combustion process of Al in different systems, it is found that the consumption rate of each gas is almost the same when the number of O atoms does not reach the stoichiometric ratio, while the oxidation reaction capacity of O2 is much larger than that of H2O and CO2 when the number of O atoms exceeds the stoichiometric ratio.