(1) Atmospheric relative humidity

 

　　At the same temperature, the percentage of the water vapor content of the atmosphere and its water vapor saturation content is called relative humidity. Below a certain relative humidity, the metal rust rate is very small, and above this relative humidity, the rust rate increases sharply. This relative humidity is called the critical humidity. The critical humidity of many metals is between 50% and 80%, and that of steel is about 75%. The relative humidity of the atmosphere has the greatest influence on the corrosion of the metal in the anti-rust treatment. When the atmospheric humidity is higher than the critical humidity, water film or water droplets appear on the metal surface. If harmful impurities contained in the atmosphere are dissolved in the water film or water droplets, it becomes an electrolyte, which intensifies corrosion.

 

　　(2) Temperature and humidity

 

　　Both atmospheric temperature and humidity affect metal corrosion. This has the following main conditions: First, the water vapor content of the atmosphere increases with the temperature; second, the high temperature promotes the intensification of corrosion, especially in humid environments, the higher the temperature, the faster the corrosion rate. When the relative humidity is low, the influence of temperature on rust is not obvious, but when the humidity is higher than the critical humidity, the amount of rust increases sharply as the temperature rises. In addition, if there is a temperature difference between the atmosphere and the metal, condensed water will form on the surface of the metal with a low temperature, which will also cause the metal to rust.

 

　　(3) Corrosive gas

 

　　The corrosive gas in the polluted air, sulfur dioxide has the greatest impact on metal corrosion, especially for steel, copper and its alloys. The sulfur dioxide in the atmosphere mainly comes from the combustion of coal. At the same time, the combustion product carbon dioxide also has a corrosive effect. Corrosive gases are mixed in the atmosphere around the plant. Such as hydrogen sulfide, ammonia, hydrochloric acid, etc. are all factors that promote metal corrosion. Of course, the oxygen in the atmosphere is the most common for metal corrosion, and it takes effect anytime and anywhere, which is self-evident.

 

　　(4) Other factors

 

　　The atmosphere contains a lot of dust, such as smoke, coal ash, chloride and other acid, alkali, salt particles, etc., some of which are corrosive, or condensation nuclei of water droplets, are also rust factors, such as chloride is considered Is the "mortal enemy" of corrosion of metals.