Little Knowledge: Basic Knowledge Of Metal Antirust

　　 Cause metal Rust Main factors:

(1) relative humidity at the same temperature, the percentage of water vapor content in the atmosphere and its saturated vapor content is called relative humidity. Below a certain relative humidity, the corrosion rate of metal is very small, and the corrosion rate increases abruptly after the relative humidity is higher. This relative humidity is called critical humidity. The critical humidity of many metals is between 50% and 80%, and steel is about 75%. Atmospheric relative humidity has the greatest influence on metal corrosion. When the atmospheric humidity is higher than the critical humidity, there will be water film or water droplets on the surface of the metal. If the harmful impurities in the atmosphere are dissolved in the water film and water droplets, the electrolyte will become more corrosive.

(2) air temperature and humidity temperature And humidity The two factors affect metal corrosion. This has the following main situations: first, the water vapor content of the atmosphere increases with the increase of temperature; second, the high temperature causes the corrosion to intensify, especially in the humid environment, the higher the temperature, the faster the corrosion rate. When the relative humidity is low, the effect of temperature on corrosion is not very obvious. However, when the temperature is higher than the critical humidity, the corrosion will increase rapidly with the increase of temperature. In addition, if there is temperature difference between the atmosphere and the metal, condensation water will be formed on the surface of the metal with low temperature and rust will also occur.

(3) Corrosive gas The corrosive gases in polluted air have the greatest influence on the corrosion of metals by sulphur dioxide, especially for steel, copper and its alloys. The main source of sulfur dioxide in the atmosphere is coal combustion. At the same time, the combustion product carbon dioxide also has corrosion effect. Corrosive gases are mixed in the atmosphere around the plant. Such as hydrogen sulfide, ammonia and hydrochloric acid are all factors contributing to metal corrosion.

(4) other factors contain a lot of dust in the atmosphere, such as smoke, ash, chloride and other acids, alkalis, salt particles, etc., some of them are corrosive, or the condensation nuclei of water droplets are also corrosion factors, such as chloride is considered to be the "deadly enemy" of corroding metal.

　　 Rust preventive methods for metals:

　　 Antirust method Preventive measures are taken for the reasons of metal corrosion. Since metal corrosion is caused by humidity, high temperature, oxygen, sulphur dioxide, chloride, dust and so on, rust prevention is necessary to avoid or slow down the metal corrosion caused by these factors. At present, the rust prevention methods are as follows: adding some elements in metal smelting, enhancing the ability of metal to resist external corrosion; making corrosion resistant surface treatment on metal products, forming surface conversion layer or adding surface coating; cathodic protection, that is, using rust inhibitor, vapor phase inhibitor, stripped plastic and sealing method to temporarily isolate metal surface from the external environment (temporary rust prevention method 1), and remove these antirust materials when metal products are used. The antirust period of this method can last several months to several years.