Ionic aggregates in steam. Part 1.—Equilibrium configurations

Abstract

Molecular-dynamics simulations have been performed for ionic aqueous aggregates in the vapour phase using the simple point-charge model to represent H₂O–H₂O interactions. To obtain equilibrium configurations efficiently by molecular-dynamics simulation, model water molecules from bulk steam were allowed to collide against the surface of the simulation sphere at the average collision rate. In this way we have obtained, for the first time, information about the configuration of ionic aggregates in model steam for two thermodynamic state points. Water molecules surrounding the ionic aggregates show liquid-like density confirming the existence of strong microheterogeneity in steam when it contains ions. The results show that the detailed distribution of H₂O in the aggregates must be known for the formulation of plausible models for ions in steam. Evidence indicates that in steam, charged aggregates are relatively stable compared with neutral ones by their greater capacity to attract water molecules towards them.