Micro-Droplets Formation During the Deliquescence of Salt Particles in Atmosphere

The formation of the electrolyte droplet caused by the deliquescence of soluble salt particles is one cause for the acceleration of atmospheric corrosion. In this paper, a lot of micro-droplets, 1 μm to ~10 μm in diameter, were observed around the edge of the main-droplet formed by the deliquescence of a single salt particle deposited on metals in atmosphere. Two preconditions were needed for the formation of micro-droplets. One was that the relative humidity (RH) in atmosphere should be over the saturated RH of the main-droplet. The other was that the metal substrate could be eroded under the main-droplet. The corrosion current was proven to be the driving force for the formation of micro-droplets by electrochemical polarization. Based on the surface analyses of scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), there were some sodium cations and a few chloride anions in micro-droplets for a main-droplet of sodium chloride (NaCl). The formation of invisible water clusters and water film, synergistic action of the oxygen reduction and the water molecule adsorption, and migration of cations in the main-droplet were regarded as the main phases for the formation of micro-droplets.