The atmospheric environment is mainly divided into a rural atmosphere, industrial atmosphere, marine atmosphere, and industrial marine atmosphere. Although these are basic atmospheric environmental conditions, in fact, in each environmental condition, the corrosion performance of industrial aluminum profiles will be very different.
Aluminum profiles can form a dense oxide film in the atmosphere. In a clean and dry continental atmosphere, corrosion takes place in a chemical process, showing that industrial aluminum profiles have high corrosion resistance. Aluminum profiles will cause severe atmospheric corrosion in the humid and polluted atmosphere. However, when the temperature is higher than the dew point, water condenses on the surface of the aluminum profile, which is prone to electrochemical corrosion. This is the main reason for the corrosion of industrial aluminum profiles in the non-polluting rural atmosphere; the air is polluted in industrial areas and the pollutants contained in the atmosphere Such as SO2, CO2, H2S, NO3, CI2 and other active gases, the gas concentration increases and the atmospheric pH decreases, thereby forming acid rain and increasing the corrosion rate of industrial aluminum profiles. There are many halogen ions in the marine atmosphere, and the CI ( -1) The concentration and the number of salt particles are high, which will reduce the corrosion resistance of aluminum profiles and accelerate the corrosion of aluminum profiles.
Itching is mainly involved in the process of electrochemical corrosion in atmospheric corrosion. Oxygen in the air dissolves in the electrolyte membrane layer present on the surface of the aluminum profile and acts as a cathode depolarizer, while the surface electrolyte layer of the aluminum profile is mainly formed by moisture in the atmosphere. The content of water vapor in the atmosphere is often expressed as relative humidity. The ratio of the water vapor pressure in the atmosphere to the saturated water vapor pressure in the atmosphere at the same temperature is called relative humidity. When the relative humidity reaches 100%, the water vapor in the atmosphere will directly condense into water droplets, which will land or condense on the surface of the aluminum profile, forming a water film visible to the naked eye. Even if the relative humidity is less than 100%, due to capillary condensation, adsorption condensation or chemical condensation, water vapor can condense on the surface of the aluminum profile into a thin, invisible water film. It is precise because of the existence of this electrolyte liquid film layer that the conditions for electrochemical corrosion are met so that the atmospheric corrosion of aluminum profiles is relatively obvious. The thickness of the liquid film layer affects the corrosion rate of the atmosphere. Therefore, the type of atmospheric corrosion can be divided according to the different humidity of the aluminum profile surface, that is, according to the presence and state of the electrolyte film layer, called dry atmospheric corrosion, Moist atmosphere corrosion, and wet atmosphere corrosion. In the case of actual atmospheric corrosion, due to changes in environmental conditions, various forms of corrosion can be interchanged. For example, initially, aluminum profiles under atmospheric corrosion type will begin to corrode in the form of atmospheric corrosion when the surrounding atmospheric humidity increases or becomes a water-absorption corrosion product. If the rain falls directly on the surface of the aluminum profile, the wet atmospheric corrosion will turn into wet atmospheric corrosion. When the water film on the metal surface is evaporated and dried after the rain, it is corroded according to the form of atmospheric corrosion, which mainly considers the two types of corrosion: wet and atmospheric corrosion.
The corrosion of atmospheric environment in the acid rain area in the west and the special atmospheric environment on the Qinghai-Tibet Plateau have a special impact on the corrosion of industrial aluminum profiles, so attention should be paid. When industrial aluminum profiles are used in the atmospheric environment of the Salt Lake area, they are easily covered by the salt layer, and the problem is not usually exposed, but once it encounters rainy weather, the corrosion becomes very serious. In the rural and general industrial atmospheric environment, the annual corrosion rate of aluminum profiles is only on the order of tens of nanometers, which will increase by an order of magnitude in the marine atmospheric environment, and in the atmospheric environment of acid rain areas, the corrosion becomes more serious.