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Amazing electrochemical reactions: What's the surprising secret behind metal corrosion?
Metal corrosion is a natural process that transforms refined metals into more stable oxides. It is the gradual deterioration of a material (usually a metal) through chemical or electrochemical reactions with its environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion. In everyday parlance, this usually means an electrochemical oxidation reaction between a metal and an oxidizing agent such as oxygen, hydrogen, or hydroxide.
Rust, the formation of red-orange iron oxides, is a well-known example of electrochemical corrosion.
This type of corrosion often produces oxides or salts of the original metal and results in the characteristic color. Corrosion can also occur in materials other than metals, such as ceramics or polymers, but in this context the term "deterioration" is more common. Corrosion reduces the usefulness of materials and structures, including mechanical strength, appearance, and permeability to liquids and gases. Some structural alloys corrode simply from exposure to moist air, but this process can be strongly affected by certain substances.
Corrosion can be localized, forming pits or cracks, or it can corrode the surface uniformly over a large area. Since corrosion is a diffusion-controlled process, this means that it will occur on exposed surfaces. Therefore, measures to reduce exposed surface activity, such as passivation and chromium conversion, can improve the corrosion resistance of materials. However, some corrosion mechanisms are less obvious and difficult to predict.
The core of the electrochemical process
The chemical process of corrosion is quite complex and can be regarded as an electrochemical phenomenon. At a particular surface of the iron, the oxidation process is taking place, and that place acts as the anode. The electrons released at this anode position move through the metal to another point where they reduce oxygen in an environment containing H+. This position acts as the cathode.
Case of battery corrosion
Battery corrosion occurs when two dissimilar metals come into contact with each other and are immersed in a common electrolyte, or when the same metal is exposed to electrolytes of different concentrations. In a battery pack, the more active metal (the anode) corrodes at an accelerated rate, while the more noble metal (the cathode) corrodes at a slower rate. This phenomenon is particularly important in the marine industry, especially where water (containing salt) comes into contact with pipes or metal structures.
Use sacrificial anodes to flexibly deal with battery corrosion. For example, zinc is often used as a sacrificial anode for steel structures.
Methods to remove corrosion
Often, corrosion products can be removed chemically. For example, phosphoric acid can be applied to iron tools or surfaces in the form of "navy glue" to remove rust. However, corrosion removal should not be confused with electropolishing, which is the removal of some layers of the underlying metal to achieve a smooth surface. The corrosion resistance of some metals is related to their intrinsic properties, which shows the importance of biological and chemical reactions in preventing corrosion.
In many cases, proper metal selection is the key to long-term performance.
Anti-corrosion strategies
There are various methods of protecting metals from corrosion, including painting, hot-dip galvanizing, cathodic protection, and combinations of these methods. For example, coatings can provide a layer of protection from direct metal contact with corrosive environments. The success of applying these protective measures depends on the quality of the seamless coverage, and even tiny imperfections can become an Achilles heel for corrosion.
In the chemical industry, hydrogen depression is a depression formed due to the interaction between corrosive media and steel pipes and hydrogen bubbles. When acidic liquids pass through steel pipes, the corrosion products interact with hydrogen bubbles, forming a frustrated gel-like substance that creates more corrosion.
Corrosion detection and prevention
The detection and prevention of corrosion can be enhanced with the help of modern technology, such as the use of sensors, monitoring equipment and material selection. Resistance to high-temperature corrosion, microbial corrosion and even metal powdering requires special attention. Designing the right environment and maintaining appropriate protection can effectively reduce the damage caused by these corrosion events, thereby enhancing material life.
When choosing the right material, it is important to consider its environmental impact and capabilities.
In summary, corrosion is a common but complex process. Understanding its mechanism not only helps prevent and control corrosion, but also improves the durability and service life of materials. In daily life, how can we face the challenge of metal corrosion more effectively?
