Atomic origin of the morphological evolution of aluminum hydride (AlH3) nanoparticles during oxidation using reactive force field simulations

Abstract

Metal hydride nanoparticles exhibit different oxidation dynamic characteristics from bulk ones due to size effects as well as the existence of M-H bonds. We used ReaxFF-lg molecular dynamics to elucidate the dehydrogenation and oxidation mechanisms of aluminum hydride nanoparticle (AHNP). Results show that the morphological evolution of AHNP is induced by temperature and structure, and classified into four shapes: sphere, notched sphere, large branch, and small string. The surface dehydrogenation and oxidation are almost co-occurring. The initial dehydrogenation inhibits the rapid oxidation of the surface layer of AHNP. The increase in temperature induces the instability of the oxide shell and provides sufficient kinetic energy for the hydrogen bubbles. As a result, the oxidation shell ruptures, and the internal hydrogen bubbles physically escape from the nanoparticles. Some simultaneous notches appear in the shell, making its appearance to be branchy at 3000 K. AHNP explodes and ejects small strings of atoms at 3500 K. We also investigated the effect of different temperatures and initial oxygen densities on the morphologies of AHNP. Our results emphasize the complicated interplay between the structural evolution of nanoparticles and environmental conditions. It provides insights into the atomic-level dehydrogenation and oxidation mechanism of metal hydride nanoparticles.