original preservation period of galvanized sheet1
What are the characteristics of corrosion of steel?Iron and steel explosion and leakage in the atmosphere, mainly dry corrosion, moisture corrosion and wetting corrosion of several forms.
Dry corrosion of iron and steel refers to the corrosion of continuous electrolyte water film on the surface of steel belt in atmospheric environment with relative humidity less than 30%. Under this condition, the corrosion rate of steel is slow, but the environmental conditions are less.
Moisture corrosion of iron and steel refers to the corrosion of iron and steel in atmospheric environment with relative humidity greater than 30% and less than 100%. In this case, dust exists on the surface of steel and micropores and cracks in the rust layer produce microadsorption, forming water film invisible to the naked eye, and electrochemical corrosion occurs under the water film, 1.The corrosion rate is relatively fast.Wetting corrosion of iron and steel refers to the corrosion of iron and steel in a humid atmosphere with relative humidity greater than 100%, when there is condensation and visible water film on the surface. Under this condition, the water film on the steel surface is thicker, which makes the diffusion rate of hydrogen dissolving towards the steel surface slower and reduces the corrosion rate.2. What are the characteristics of zinc corrosion?Zinc is a more active metallic element than iron, and is more likely to be oxidized and corroded.Zinc also reacts with oxygen in the air to form a hydrogen front in a dry, waterless environment. This is different from the "red rust" after iron oxidation. Its color is white, so it is called "white rust". The reflection is as follows: 22n+ 02-22noIn humid air, electrochemical corrosion involving oxygen takes place and oxidizing front is formed. The C02 in the air will be further reflected with ZNO, which becomes ZNC03, and its color becomes a little black, forming black spots on the surface of zinc, so it is called ao "shine spots".In this way, in the atmospheric environment, the surface of zinc is covered with an oxide film composed of hydrogenation front, zinc carbonate and zinc hydroxide. This oxide film is relatively compact and has good adhesion performance, which can isolate the external oxygen from the internal tissue and prevent the internal zinc substrate from being further oxidized. In terms of corrosion loss ratio, the corrosion loss of steel is 15"30 times that of zinc. However, in the polluted atmosphere, the corrosion property of zinc is greatly affected.