When galvanized steel is exposed to the air, several phenomena such as dry corrosion, wet corrosion and wet corrosion will occur.
Dry corrosion of galvanized steel refers to the corrosion in which a continuous electrolyte water film is not formed on the surface of the steel in ambient air with a humidity below 30%. Under such circumstances, the corrosion rate of steelslower. However, there are few such environmental standards.
The wet corrosion of galvanized steel sheets refers to the corrosion of steel in ambient air with air humidity exceeding 30% and lower than 100%. In this case, there is dust on the surface of the steel and microscopic particles in the rust layer.
Holes and gaps cause microscopic absorption, producing shrinkage water that is invisible to the human eye. The galvanic principle occurs under the shrinkage water, and the corrosion rate is relatively rapid.
Wet corrosion of galvanized steel sheets refers to the corrosion of galvanized steel sheets when there is solidified shrinkage water on the surface that is visible to the human eye in humid and cold ambient air with air humidity exceeding 100%. Under such circumstances, the shrinkage water on the surface of the steel is thicker, which causes the oxygen to diffuse out of the surface of the steel more slowly after melting, reducing the corrosion rate. In fact, the corrosion of steel is closely related to the shrinkage of water on the surface between the two. It is also due to the presence of water, which dissolves CO2 in the water, causing the iron to produce weak electrolytes, resulting in a series of weak electrolyte reactions.
The CO2 in the gas continues to dissolve in the water, and the reaction continues. Since the main product of reaction is red, the material after iron oxidation is generally called "red rust". Red rust is very loose and melts easily. It cannot protect the surface of the steel from being corroded again, and it will promote the corrosion of the steel until it is completely corroded. This is a characteristic of steel. Because of this, steel must be coated with other metals or metal protective layers on the surface to effectively prevent corrosion of the steel.
