Reactive molecular dynamics simulations on the pyrolysis of SF6

Abstract

There are occasionally partial over-thermal faults in gas-insulated equipment inducing SF6 insulating medium to dissociate. It remains unclear at the atomic scale how this chemically stable gas pyrolyzes at high temperatures. To date, there is a lack of micro-level investigations on the molecular behavior of SF6 at high temperatures. In particular, it requires an effective force field to characterize the evolution of the reactions involving SF6 and low-fluorine sulfides. The paper aims to fill the gap in this field by performing reactive molecular dynamics (MD) simulations. In this work, MD simulations were carried out on a system consisting of more than 100 SF6 molecules using a new developed reactive force field The dissociation of SF6 and the subsequent reactions involving low-fluorine sulfides at high temperatures were simulated. The variation of all species in the system were recorded to investigate the effects of the temperature and pressure on the pyrolysis process. The obtained data was then used to establish the relationship between the reaction rate and temperature, thereby formulating Arrhenius law. Furthermore, the trajectories of SF6 and other species were observed at the atomic level. Snapshots of key frames during the reaction helped us to explore the interaction mechanism of free F atoms with SF6 molecules and SF5 fragments. It was found that the early dissociation of SF6 mainly comes from the thermal vibrations of the molecule itself, while the later decomposition of SF6, SF5 and others is related to high-speed collisions by F atoms. This work contributes to the understanding of the mechanism of SF6 pyrolysis and lays a foundation for more MD investigations.