What Is Metal Corrosion and Why Does It Occur?

Corrosion is a broad term that refers to a variety of interactions between a material and its environment that result in a loss of material qualities.

Diffusion controlled growth of oxide layers can be caused by interaction with ambient oxygen. These may act as a passivate, protecting the substance from further oxidation. Aqueous corrosion can occur in a moist environment due to electrochemical processes that rely on metal ion movement and reactivity. The corrosion rate is influenced by gradients of metallic and electrolytic ion concentrations, temperature, ambient pressure, and the presence of other metals, bacteria, or active cells.

The rate of corrosion or material deposition can be accelerated or inhibited by applying electric fields to corroding systems. 

Definition of Corrosion

Corrosion is a natural process that transforms pure metals into undesirable chemicals when they react with fluids such as water or air, according to the definition. As metal interacts with the environment, this reaction causes damage or disintegration, which gradually spreads throughout the entire bulk of the metal.

crevice corrosion

Crevice corrosion occurs when a stagnant solution in crevices, such as around the edges of nuts and rivet heads, attacks metal surfaces. When dust, grit, and other corrosive particles are accumulated on surfaces, they create an environment in which water collects and corrodes the component. It can happen when two metals collide or when a metal collides with a nonmetal. This damages the metallic portion, which is triggered by a chemical concentration gradient.

Outside the crevice, oxygen causes an electrochemical concentration cell. The air present in this differential aeration cell is oxygen. The pH and oxygen content rise in the crevice (the cathode). The chlorides, on the other hand, are at a lower level.

Hydroxyl ions react with Fe⁺⁺

Corrosion is an electrochemical reaction that can take several forms, including chemical corrosion and air corrosion, the latter being the most prevalent. Rust forms when acidic chemicals (such as water) come into contact with metals like iron and steel. Rust is the result of iron (Fe) particles being exposed to oxygen and moisture and corroding steel (e.g., humidity, vapor, immersion). When steel is exposed to water, the iron particles dissolve due to the acidic ions in the water. After that, the iron particles are oxidised, resulting in the creation of Fe++. Two electrons are released when Fe++ is produced and pass through the steel to the cathodic region.

These electrons climb up and produce hydroxyl ions when exposed to oxygen (OH). Rust is formed when the hydroxyl ions combine with the Fe++ to generate hydrous iron oxide (FeOH). The corrosion pit where the affected iron particles were has now become a corrosion product, and the corrosion product is where they are currently (rust).

Corrosion can happen at any time, depending on the metal’s surroundings. However, because air corrosion is so common, it is advised that efficient corrosion protection measures be implemented.

temperature resistance

High temperature corrosion plays an increasingly essential role in the selection of materials, in particular within the power generation industry. The desire for engines to operate at higher temperatures to attain greater engine efficiencies, along with continual exposure to harsh conditions and high pressures, means that materials are being pushed past their original design limits.

Conclusion

The Deal-Grove model is frequently used to predict the formation of the oxide layer. It aids in the prediction of oxide layer growth. In the meantime, corrosion is measured using the weight loss method.

In the weight loss method, a clean weighted piece of alloy or metal is exposed to a corrosive environment for a specified period of time, after which the corrosion is removed and the piece is weighed to calculate the weight loss of the metal or alloy.Corrosion has a variety of consequences on various materials. Some of them are listed below:As a result of this process, natural resources are squandered.It can also result in dangerous situations, such as the deterioration of a structure made of items.Corroded materials can lead to accidents.It has the potential to cause pipelines to burst or crash. As a result, corrosion prevention is critical.Copper corrosion, iron corrosion, and silver tarnishing are some examples of corrosion.