Atomistic insights into the reaction mechanism during the collision between Ni and Al nanoparticles in an oxygen environment

The chemical reaction between Ni and Al serves as a typical subject for the impact energy release of active metals. In fact, oxygen in the air will inevitably participate in the reaction process. This study systematically explores the various reaction mechanisms during the collision between Ni and Al nanoparticles in an oxygen environment through molecular dynamics simulations with reactive force fields. After elastic-plastic deformation, both Al and Ni nanoparticles can experience successive melting and micro-explosion triggered by exothermic reaction. Then, Al and Ni clusters are ejected into oxygen, resulting in a higher degree of oxidation reaction than intermetallic reaction. Moreover, the coupled development of intermetallic reaction and oxidation reaction is analyzed. Part of Al and Ni will form Al-O clusters and Ni-O clusters, respectively. The Al-Ni-O clusters are also observed via two pathways: (1) Al and Ni nanoparticles collide to induce intermetallic reactions forming Ni-Al compounds, followed by oxidation reactions; (2) Al-O clusters and Ni-O clusters react separately with Ni or Al. The oxidation clusters mainly exhibit approximately spherical and short-chain shapes with their size distribution conforming to the modified power-law distribution formula. Finally, the Al-Ni-O clusters are the low-coordination structure and account for about 70 % of the oxidation products in our simulation conditions. Enhancing velocity will cause the fragmentation of Al nanoparticles and accelerate the micro-explosion of Ni nanoparticles, consequently raising the reaction rate, and increasing the size of the nanoparticles raises the final number of Ni-Al intermetallic bonds, oxidative bonds, and the size of oxidation clusters. This study provides new insights into the potential reaction mechanisms of the active metal materials in the air environments.