Metal products in hardware goods primarily face corrosion prevention challenges in storage. Metal corrosion is caused by chemical or electrochemical reactions with the surrounding environment. Depending on the medium, it is categorized into atmospheric corrosion, soil corrosion, seawater corrosion, bacterial corrosion, and more. Atmospheric corrosion is most common, as metal products are constantly exposed to the atmosphere during processing, transportation, and storage, providing constant conditions for atmospheric corrosion to occur.
conventionally, the corrosion or discoloration of metal caused by oxygen, moisture, and other pollutants in the atmosphere is referred to as rusting. After metal products rust, mild cases may affect their appearance quality, while severe cases can impact their usability, even leading to discard. Therefore, proper storage and rust prevention are crucial in handling metal products.
Primary Causes of Metal Rusting★
1. Relative humidity refers to the percentage of water vapor content in the atmosphere compared to its saturation content at the same temperature. Below a certain relative humidity, the rate of metal corrosion is minimal, but it sharply increases once this relative humidity is exceeded. This relative humidity is known as the critical humidity. The critical humidity for many metals ranges between 50% to 80%, with steel approximately at 75%. The impact of atmospheric relative humidity on metal corrosion. Once the atmospheric humidity surpasses the critical humidity, a water film or droplets form on the metal surface. If harmful impurities in the atmosphere dissolve into the water film or droplets, they become electrolytes, exacerbating corrosion.
2. Atmospheric temperature and humidity both have an impact on metal corrosion. The following are some key scenarios: The water vapor content in the atmosphere increases with rising temperatures; higher temperatures accelerate corrosion, particularly in humid environments, where the higher the temperature, the faster the corrosion rate. At low relative humidity, the effect of temperature on corrosion is not very pronounced, but when above the critical humidity, as temperatures rise, the amount of corrosion increases dramatically. Additionally, if there is a temperature difference between the atmosphere and the metal, condensation water forms on the cooler metal surface, also leading to metal corrosion.
3. Corrosive gases pollute the air, with sulfur dioxide being particularly harmful to metal corrosion, especially steel, copper, and their alloys. The primary source of sulfur dioxide in the atmosphere is the burning of coal. Additionally, the combustion byproduct carbon dioxide also exhibits corrosive properties. The air around the factory is mixed with corrosive gases, such as hydrogen sulfide, ammonia, and hydrochloric acid, which accelerate metal rusting. Moreover, if there is a temperature difference between the atmosphere and the metal, condensation water forms on the cooler metal surface, leading to rusting.
4. Other factors include the presence of a large amount of dust in the atmosphere, such as smoke, soot, chlorides, and other acidic, alkaline, and salt particles. Some of these have corrosive properties or serve as nuclei for water droplets, all contributing to rusting. Chlorides, for instance, are considered the "arch敌人" of corroding metals.
Corrosion Prevention Methods Corrosion prevention methods involve taking preemptive measures against the causes of metal rust. Since metal rust is caused by factors such as humidity, high temperatures, oxygen, sulfur dioxide, chlorides, and dust, corrosion prevention aims to avoid or slow down the rusting effects of these elements.
Current rust prevention methods include:
By adding certain elements during metal smelting, we enhance the metal's resistance to external medium erosion.
2. Conduct corrosion-resistant surface treatment on metal products, forming a surface conversion layer or adding a surface coating.
3. Cathodic protection involves using methods such as permanent gas-phase rustproof bags, rustproof oils, aqueous rustproof liquids, and rustproof papers to temporarily isolate the metal surface from the external environment (a temporary rustproofing method). These rustproofing materials can also be easily removed when the metal products are in use. The rustproofing period with this method can last from several months to several years and is widely applied. The next step can be directly carried out after the surface is dried.
