Study Of Micro-droplets Phenomenon During The Initial Stage Of Atmospheric Corrosion

Atmospheric corrosion is the most widespread corrosion problem known to mankind and it has a close relation with the electrochemical corrosion. It can be defined as the corrosion of metal materials exposed to air and its pollutants. The process of atmospheric corrosion is accelerated with the formation of an electrolyte droplet, which was named as main-droplet here, or a thin electrolyte layer through the adsorption of water vapor by the deposited salt particle at certain relative humidity. The formation of the electrolyte droplet or thin electrolyte layer electrochemically changes the surface situation of materials from homogeneity to heterogeneity. Therefore, a considerable potential difference or corrosion current is established in the electrolyte droplet or thin electrolyte layer, and the atmospheric corrosion is ignited and accelerated due to the existence of corrosion cell.Although much information has obtained about the atmospheric corrosion process, yet even today it is not fully understood. Recently, a lot of micro-droplets,μm range in diameter, were observed around the edge of main-droplet formed by the deliquescence of salt particles deposited on metals in atmosphere. Some of characteristics of micro-droplets were that they were caused by the type of main-droplet and formed only when the metal can be corroded for the main-droplet. Obviously, the phenomenon of micro-droplets formation may be related to the atmospheric corrosion process.Micro-droplets can appear under natural condition and artificial polarized condition. At certain relative humidity, corrosion center which is formed because of deposited inorganic salt particle on the metal surface result in formation of micro-droplets, then the corrosion will develop to all metal surface. So to know the reason for the formation of micro-droplets has important significance for studying...