Introduction

Corrosion of metals is an essential worry for engineers. The science of corrosion is intricate; it very well may be considered an electrochemical reaction(Redox Reaction).

The electrons released at this anodic spot travel through the metal and go to one more right. On the money, the metal and reduce oxygen at that spot in presence of H+ (which is accepted to be accessible from H2CO3 formed because of dissolution of carbon dioxide from the air into water in soggy cool of atmosphere. Hydrogen ions in water may likewise be accessible because of the dissolution of other acidic oxides from the atmosphere). This spot acts as a cathode.

Corrosion is the natural electrochemical process that converts a refined metal into a more chemically stable form. These may include oxide, hydroxide, carbonate or sulfide etc. It is a slow but gradually increasing process in which the destruction of metals takes place by chemical reactions or electrochemical reactions with nature.

Preserving infrastructure

The ability of electrochemical processes to break compounds down into elements or to create new compounds can be destructive as well as productive. Corrosion is an all-too-common result of electrochemical redox reactions between materials and substances in their environment.

What is Corrosion?

Corrosion is simply known as the complete decay of a metal block or metal sheet under the influence of water and oxygen. The chemical reaction that takes place during the corrosion is also redox in nature since both the reduction and oxidation occur simultaneously. 

Related: you can get benefits by using the balancing redox reactions calculator which provides you online calculation for calculating the rate of redox reaction.

Types of Corrosion

• Electrochemical corrosion

The most common type of corrosion is the one resulting from an electrochemical redox reaction. In this process, most of the metal atoms of the sheet get oxidized by losing the electrons to the oxygen of either water or air. This causes the sheet to weaken and damage completely. All those metals that possess higher tendencies of losing electrons/undergo oxidation/higher electropositive, undergo this type of electrochemical corrosion. Oxygen, after accepting the electrons from the metal, gets reduced and forms a metal oxide that appears as a reddish-brown colour cover sheet. 

• Galvanic corrosion

The second type of corrosion is one known as galvanic corrosion and it occurs when both the processes of redox and oxidation take place on different pieces of metal, other than a single metal sheet. However, these two metal pieces should be in contact with each other to donate-accept electrons. In this way, the systems exhibit a kind of galvanic cell where one metal piece is losing electrons under the influence of air, water, acid, or temperature, and the other metal piece is accepting the electrons. 

In a galvanic couple, the anode part is the more active metal that corrodes at a very high rate and the more noble metal (the cathode) corrodes at a slower rate. When these cathodes and anodes are immersing separately, each metal corrodes at its own rate without any comparison i.e. active metal or noble metal. What type of metal(s) to use is readily determine by the galvanic series.

Corrosion Removal

No doubt, it is naturally possible to chemically remove the corrosion of products or metals. For example, if we take the phosphoric acid in the form of naval jelly, It is greatly use for refining the tools or refining the surfaces to remove rust from them.

Corrosion removal should not confuse with electropolishing. which removes some layers of the underlying metal to make a smooth surface. For example, phosphoric acid may also use as an electropolish copper. But it does this by removing copper, not the products of copper corrosion.

What is Rusting?

Rusting is the coat of the rust that is produced on the surface of the iron. Rusting is an oxidation reaction. In an oxidation reaction, there is a loss of electron occurs. In general, there is a loss of hydrogen takes place for the gain of oxygen. Oxidation calculator is one of the best online tools which provides us with the number of electron losses or gains by atom. We can find the oxidation state of elements involved in rusting (oxidation reaction) by using it.

In the process of rusting, the iron has reacted with water along with oxygen to form hydrated iron(III) oxide. Thus this is a rust material.

Corrosion Vs Rusting

Both the terminologies corrosion and rusting are different and you shouldn’t confuse them up. The term corrosion refers to the chemical disintegration of any material, including metal, nonmetal, ceramics, and even polymers that decay in the presence of air and chemicals.  

On the other hand, the term rusting is only specified for the chemical disintegration of iron and iron alloys that occurs in the presence of moisture and air. 

The process of rusting may or may not be a part of corrosion and the product of rusting is only the iron oxides. Whereas any type of metal oxide or oxides of salts may produce as the product of corrosion. 

Chemistry of Corrosion/Rusting

The process of corrosion gets the driven force when an exposed or uncovered surface of a metal sheet comes into contact with gas or liquid oxygen and the process gets even faster in the presence of salts, acids, or higher temperatures. During the corrosion, iron atoms react with oxygen and get oxidize by releasing the electrons as follows

Fe – – – Fe2+ + 2e–

On the other hand, the oxygen atom, on coming in contact with the metal surface. It gets reduce to water by accepting the electrons as follows

O2 + 4H+ + 4e – – – > 2H2O

On combining both the oxidation and reduction halves, the overall reaction will be as follows

2Fe + O2 + 4H+ – – – > 2Fe2+ + 2H2O

When the iron ions, Fe2+, further react with oxygen atoms, hydrated iron oxide is formed that appears as a reddish-brown color over the surface.

Fe2+ + O2 + 2H2O – – – > 2Fe2O3•xH2O + 8H+ 

The number of water molecules may vary depending upon the extent of humidity. So that’s why it will show as an x. 

Prevention Techniques

In some redox reactions, the products of corrosion like patina or rust make a layer over the surface. This is aapplying to protect the metal. If any such thing happens, it’s better not to scrap away this protective layer. Since doing so could restart the process of corrosion to eat away the leftover metal. 

However, this kind of protective coating doesn’t form during the rusting of iron. The more and more new and fresher iron atoms keep on decaying, exposing newer iron. 

Thus, the only way to prevent the iron sheets from rusting away is to paint them up. The layer will act as a preventive coating. This will keep the oxygen and water molecules from coming in contact with iron atoms. 

Another way to prevent rusting is to form an alloy of iron with another metal like chromium. When a thin layer of chromium is introducing at the surface of an iron sheet. It reacts with atmospheric oxygen to form chromium oxide which, in turn, acts as a protective coating. 

Similarly, you can also use drying or water-repelling agents to prevent the process of rusting. You can also utilize the galvanizing/electroplating techniques. 

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