Melting Point and Crystal Growth Kinetics of Metals and Metal Oxides Using Reactive Force Fields: The Case of Aluminum and Alumina

Alumina and aluminum
are strategic materials employed in energy
applications, with metal aluminum being interesting in phase change
material applications. Therefore, the theoretical description of the
thermophysical properties of these materials represents an important
objective. Here, we investigate the liquid–solid coexistence
properties of aluminum and alumina using a state-of-the-art reactive
force field (ReaxFF) and molecular dynamics simulations. Aluminum
features ultrafast crystal growth, which enables the direct determination
of its melting temperature via direct coexistence simulations (858
± 2 K). However, at standard pressure, alumina is easily trapped
in a glass state, preventing the application of the direct coexistence
method. We demonstrate that direct coexistence can be used at high
pressures above 2 GPa, where alumina features a higher melting temperature,
and the liquid–solid interface exhibits enhanced dynamics.
Our approach opens a route to obtain the melting temperature of ReaxFF
alumina at standard pressure (1670 ± 10 K) and, more generally,
a viable method for calculating the melting point of metal oxides
via direct coexistence simulations. We further investigated the dynamics
of crystal growth of the solid–liquid aluminum and alumina
interfaces.