A reactive force field molecular dynamics simulation of nickel oxidation in supercritical water

The atomistic mechanism of nickel (Ni) oxidation in supercritical water (SCW) is investigated using molecular dynamics simulations with a reactive force field. The oxidation kinetics of Ni surfaces in SCW at 300−800 °C and 26−164 kg/m³ are simulated. The adsorption, dissociation, and deprotonation processes of water, and the hydroxylation and oxidation processes of Ni are tracked. The oxidation potential of SCW is found to be higher than that of water at normal state. Charge analysis of deprotonation reveals that the dissociation of water is more likely to be a homolytic reaction instead of a heterolitic one under the supercritical state of relatively high temperatures and low densities. Oxidation in SCW prefers the free radical reaction pathway to the ionic pathway, which appears a gas/steam oxidation scope instead of aqueous oxidation. Reaction rate increases with increased temperature and density of SCW.