Corrosion, Rusty Iron!

One of the most common phenomena we see in our daily lives is corrosion. You've probably noticed that some iron objects are covered with an orange or reddish-brown colored layer at some point. The formation of rust on iron is perhaps the most well-known example of corrosion. When iron is exposed to oxygen and water, it rusts (oxidizes). Corrosion is commonly defined as the electrochemical degradation of metals. Corrosion can be seen in the formation of rust on iron, tarnish on silver and the blue-green patina that develops on copper. 

In general, corrosion is a process that converts refined metals into more stable compounds such as metal oxides, metal sulfides, or metal hydroxides. Similarly, iron rusting involves forming iron oxides due to the action of atmospheric moisture and oxygen. When we look at the science behind corrosion, we can say that it is a spontaneous/irreversible process in which metals transform into more stable chemical compounds such as oxides, sulfides, hydroxides, and so on. In this post, we will delve deeper into the concept of corrosion and understand its various factors such as its meaning, types, prevention, and more.

What exactly is corrosion? 

It is essentially defined as a natural process that causes pure metals to transform into undesirable substances when they react with substances such as water or air. This reaction causes metal damage and disintegration, beginning with the exposed portion of the metal and spreading to the entire bulk of the metal. Corrosion is typically an unfavorable phenomenon because it interferes with the desirable properties of the metal. Iron, for example, is known to have high tensile strength and rigidity (especially alloyed with a few other elements). Rusting, on the other hand, causes iron objects to become brittle, flaky, and structurally unsound. Corrosion, on the other hand, is a diffusion-controlled process that occurs primarily on exposed surfaces. As a result, in some cases, attempts are made to reduce the activity of the exposed surface and increase the corrosion resistance of a material. Passivation and chromate conversion are examples of processes used. Some corrosion mechanisms, on the other hand, are not always visible and are even less predictable.

Are All Metals Corrodible?

Metals higher in the reactivity series, such as iron and zinc, corrode easily, whereas metals lower in the reactivity series, such as gold, platinum, and palladium, do not corrode. The reason for this is that corrosion involves the oxidation of metals. The tendency to oxidize decreases as we move down the reactivity series.

Corrosion rate depends on:-

Metals are exposed to air containing gases such as CO2, SO2, SO3, and others increasing the chance of corrosion of metals. Metals exposed to moisture, particularly salt water have a high corrosion rate. The acid in the atmosphere: Acids can easily accelerate the corrosion process. As the temperature rises, so does corrosion. The nature of the first oxide layer formed also determines the corrosion rate: some oxides, such as Al2O3, form an insoluble protective layer that can prevent further corrosion. Others, such as rust, easily crumble and expose the remaining metal.

How could it affect our life?

Corrosion can have varying degrees of impact on a wide range of things. As a result, it primarily wastes natural resources. Furthermore, it can lead to dangerous situations such as building structures becoming weak and unstable, accidents caused by corroded parts, and other unwelcome failures such as cracked pipelines, bridge collapses, transport vehicle crashes, and other disasters. The annual global cost of metallic corrosion is estimated to be more than $2 trillion, but experts believe that proper corrosion protection could save 25 - 30% of this cost. Poorly planned construction projects can result in corroded structures that must be replaced, wasting natural resources and contradicting global sustainability concerns. Corrosion can also result in safety concerns, loss of life, additional indirect costs, and reputational damage. That's why it is critical to monitor and prevent corrosion at all costs.

Prevention:-

Corrosion is prevented by protective coatings. Metals can be protected from corrosion by applying protective coatings that act as a barrier to water and oxygen. This coating can be applied by oil greasing, painting, or electroplating with a different metal. Electroplating is accomplished through the electrolysis process. Electrolysis allows for the application of a thin layer of metal to an object. The object is at the cathode, and the plating metal is at the anode. The electrolyte is made up of plating metal ions. Aluminium oxide shields the metal. Aluminium oxide is a coating that is applied to aluminum. This oxide layer on the surface of aluminium protects the metal from further corrosion. Electroplating has a variety of applications. Metals are less likely to corrode or be damaged when they are electroplated. It also enhances the aesthetics and appearance of metals, such as silver-plated cutlery.