Atomistic-Scale Analysis of Carbon Coating and Its Effect on the Oxidation of Aluminum Nanoparticles by ReaxFF-Molecular Dynamics Simulations

Abstract

We developed a ReaxFF reactive force field for Al/C interactions to investigate carbon coating and its effect on the oxidation of aluminum nanoparticles (ANPs). The ReaxFF parameters were optimized against quantum mechanics-based (QM-based) training sets and validated with additional QM data and data from experimental literature. ReaxFF-molecular dynamics (MD) simulations were performed to determine whether this force field description was suitable to model the surface deposition and oxidation on complex materials (i.e., carbon-coated ANPs). Our results show that the ReaxFF description correctly reproduced the Al/C interaction energies obtained from the QM calculations and qualitatively captured the processes of the hydrocarbons’ binding and their subsequent reactions on the bare ANPs. The results of the MD simulations indicate that a carbon coating layer was formed on the surface of the bare ANPs, while H atoms were transferred from the hydrocarbons to the available Al binding sites typically without breaking C–C bonds. The growth of the carbon layer depended strongly on the hydrocarbon precursors that were used. Moreover, the MD simulations of the oxidation of the carbon-coated ANPs indicate that the carbon-coated ANPs were less reactive at low temperatures, but they became very susceptible to oxidation when the coating layer was removed at elevated at elevated temperatures. These results are consistent with the experimental literature, and thus, the ReaxFF description that was developed in this study enables us to gain atomistic-scale insights into the role of the carbon coating in the oxidation of ANPs