Abstract
Corrosion is a natural processes that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of iron objects or structures. This rust is formed from a redox reaction between oxygen and iron in an environment containing water (such as air containing high levels of moisture). The rusting of iron is characterized by the formation of a layer of a red, flaky substance that easily crumbles into a powder.
Introduction
Corrosion is one of the most common phenomena that we observe in our daily lives. You must have noticed that some objects made of iron are covered with an orange or reddish-brown coloured layer at some point in time. The formation of this layer is the result of a chemical process known as rusting, which is a form of corrosion.
It is basically defined as a natural process that causes the transformation of pure metals into undesirable substances when they react with substances like water or air. This reaction causes damage and disintegration of the metal, starting from the portion of the metal exposed to the environment and spreading to the entire bulk of the metal.
Corrosion is usually an undesirable phenomenon since it negatively affects the desirable properties of the metal. For example, iron is known to have good tensile strength and rigidity (especially alloyed with a few other elements). However, when subjected to rusting, iron objects become brittle, flaky, and structurally unsound. On the other hand, corrosion is a diffusion-controlled process, and it mostly occurs on exposed surfaces. Therefore, in some cases, attempts are made to reduce the activity of the exposed surface and increase a material’s corrosion resistance. Processes such as passivation and chromate conversion are used for this purpose. However, some corrosion mechanisms are not always visible, and they are even less predictable.
On the other hand, corrosion can be classified as an electrochemical process since it usually involves redox reactions between the metal and certain atmospheric agents such as water, oxygen, sulphur dioxide, etc.
Objective
To understand the factors affecting corrosion using iron nail in different environments and how to overcome corrosion.
Samples
Taking iron nails , test tube, cotton , calcium carbonate, vinegar, salt water
Methods
Taking 4 test tube and label them 1 to 4. Put the iron nails , one each in the four test tube drop a small piece of moist cotton in the first test tube and keep it exposed to atmospheric air. In the second test tube, put some quick lime and kept it closed. In the third test tube pour some sodium chloride solution such that half of the nail immersed in it. In the fourth test tube pour some dilute hydrochloric acid or vinegar to immerse half of the nail.
Observe the changes that occur to the iron nails after one week.
Results and discussion
The iron nails in the calcium carbonate doesn't undergo rusting. Other three nails in the test tube undergo rusting. The iron nails in the vinegar, moist cotton and sodium chloride solution undergo fast rusting.The exposure of iron (or an alloy of iron) to oxygen in the presence of moisture leads to the formation of rust. This reaction is not instantaneous, it generally proceeds over a considerably large time frame. The oxygen atoms bond with iron atoms, resulting in the formation of iron oxides. This weakens the bonds between the iron atoms in the object/structure.
The reaction of the rusting of iron involves an increase in the oxidation state of iron, accompanied by a loss of electrons. Rust is mostly made up of two different oxides of iron that vary in the oxidation state of the iron atom.
Conclusion
Rusting causes iron to become flaky and weak, degrading its strength, appearance and permeability. Rusted iron does not hold the desirable properties of iron. The rusting of iron can lead to damage to automobiles, railings, grills, and many other iron structures.
The collapse of the Silver Bridge in 1967 and the Mianus River bridge in 1983 is attributed to the corrosion of the steel/iron components of the bridge. Many buildings made up of reinforced concrete also undergo structural failures over long periods of time due to rusting.
Rusted iron can be a breeding ground for bacteria that cause tetanus. Cuts from these objects that pierce the skin can be dangerous.
Since rusting occurs at an accelerated rate in humid conditions, the insides of water pipes and tanks are susceptible to it. This causes the pipes to carry brown or black water containing an unsafe amount of iron oxides.
Many factors speed up the rusting of iron, such as the moisture content in the environment and the pH of the surrounding area. Some of these factors are listed below.
- Moisture: The corrosion of iron is limited to the availability of water in the environment. Exposure to rains is the most common reason for rusting.
- Acid: if the pH of the environment surrounding the metal is low, the rusting process is quickened. The rusting of iron speeds up when it is exposed to acid rain. Higher pH inhibits the corrosion of iron.
- Salt: Iron tends to rust faster in the sea, due to the presence of various salts. Saltwater contains many ions that speed up the rusting process via electrochemical reactions.
- Impurity: Pure iron tends to rust more slowly when compared to iron containing a mixture of metals.
The size of the iron object can also affect the speed of the rusting process. For example, a large iron object is likely to have small deficiencies as a result of the smelting process. These deficiencies are a platform for attacks on the metal from the environment.
Galvanization is the process of applying a protective layer of zinc on a metal. It is a very common method of preventing the rusting of iron.Providing the metals with an electric charge can help inhibit the electrochemical reactions that lead to rusting Many types of coatings can be applied to the surface of the exposed metal in order to prevent corrosion. Common examples of coatings that prevent corrosion include paints, wax tapes, and varnish.Smaller objects are coated with water-displacing oils that prevent the rusting of the object. Many industrial machines and tools made of iron are coated with a layer of grease, which lubricates the metal to reduce friction and prevents rusting at the same time.
