Welcome to MindMentor!

Corrosion

Although metals may appear to be strong and durable, they can be slowly damaged over time. How come shiny metals appear to have their value and attractiveness removed without anyone physically interacting with them? Why do objects like the old gate, school railing, bicycle chain, and metals lose their luster and become rough and dull?

This is not a magical process.

In chemistry, rusting, or slowly damaging metals, is a process is called corrosion. Corrosion is a natural process whereby a metal reacts with the environment and is converted into a more stable form. Corrosion is significant because it

• Weakens metal structures
• Increases costs for repairs
• Affects the safety of bridges, buildings, and machines
• Shows a good example of chemistry in real life.

Corrosion understanding is significant to protecting useful metals and developing advanced technologies.

What is Corrosion?

The definition of Corrosion is damage to a metal due to slow reactions occurring over a long period of time. Metal extractive processes use a significant amount of energy. Due to this, all metals have a natural tendency to undergo the processes of corrosion, as they want to be in a lower energy and more stable state.

More simply put, metals undergo corrosion because they want to return to their more stable state, and the available environment provides the metals with the means to do so (i.e. oxygen, water, and salts, etc).

This slow and gradual chemical change is what we call corrosion.

As an example, rust forms on iron, a green layer covers copper, and older silver jewelry turns black.

Corrosion, while noticeable, is less obvious than the damage caused by fire. Unlike fire, corrosion is slow and silent. This means it can be present, causing significant damage, long before it is noticed.

What causes metals to corrode?

The high corrosion rates observed in t outer layer of metals can be attributed to the metal's extractive chemical state. Each time a new metal is uncovered, it is at a high energy, high potential state and encased in a more stable, less energetic state. Therefore, the energetic metal will corrode to a more stable state (i.e. less energetic) due to the reactions with the surroundings as described below.

Corrosion is more likely to occur with

• A reaction with the oxygen, water, and moisture present in the environment
• A chemical reaction with any acids and/or salts
• The level of moisture present to facilitate the reactions

As we all are aware, metals that are left outdoors and those in the ocean show obvious signs of corrosion and rusting. This also explains why more rusting occurs in coastal areas compared to arid areas and deserts.

Rusting: A Unique Form of Corrosion

Rusting is a specific and prevalent type of corrosion that only affects iron and steel, and occurs when the following three components simultaneously present:

When all three components are present, an iron reaction occurs that results in the formation of oxidized iron, commonly referred to as rust.

The characteristics of rust are:

• reddish-brown coloration,
• flakiness and weakness, and
• porous composition, allowing for additional air and moisture to penetrate the composition.

Rust formation means that for construction materials such as iron and steel, the formation of rust does not offer protection to them. Instead:

• rust continues to form and spread,
• the iron or steel in the construction materials continues to weaken,
• the construction materials may lose the structural integrity.

This is why rusted bridges, pipelines, and tools are dangerous if the rusted materials are not properly treated.

The Science Behind Forming Corrosion

Rusting is a type of corrosion that occurs through oxidation and reduction, also described as a type redox reaction.

• 1) The iron or steel construction alloys lose electrons through an oxidation reaction.
• 2) The new compound develops through a reduction reaction.
• 3) Oxygen, in conjunction with moisture, gains electrons.

In the case of iron oxidation, iron oxidation occurs through the loss of electrons, and water and oxygen vapor in the air are electrochemically active.

Because corrosion occurs in an electrochemical process, the idea contributes to the effective management of corrosion prevention.

Different Conditions for Corrosion

The factors that influence the corrosion process vary from place to place. Depending on the conditions applied, corrosion can happen very quickly in some places and in some places can take a long time to happen.

The factors are as follows:

• Water Presence: Dry air can slow down corrosion whereas wet air can speed it up.
• Level of Oxygen: More O2 = More Corrosion
• Salts: Salt water speeds up rusting because it conducts electricity.
• Acidity: Corrosion increases from air pollution and acid rain.
• Temperature: Corrosion is faster in places that are hotter than in places that are colder.
• Nature of the Metal: Some metals are more favorable and corrode faster compared to others.

Examples are:

• Rusting of Iron occurs faster at seas.
• Aluminum develops a thin layer of oxide which protects it from corrosion.
• Gold is very unreactive so it doesn't corrode easily.

Forms of Corrosion

Based on the conditions applied and the materials used, corrosion can take on different forms. Some of the most common forms of corrosion are:

• Uniform corrosion is where corrosion is consistent and uniform over the entire surface. The metal becomes thinner over time.
• Localized corrosion: corrosion occurs in specific localized areas. Small pits or holes can develop and they are very difficult to identify at first because they are very small.
• Galvanic corrosion: occurs when two metals of different reactivity are joined together in a wet or moist environment. The metal that is more reactive undergoes faster corrosion, while the metal that is less reactive is protected from corrosion.
• Crevice corrosion. This occurs in narrow places or gaps where water is trapped or where it is difficult for the water to flow. In such areas, the supply of oxygen is limited and thus corrosion becomes concentrated in those specific areas, and corrosion happens in those areas quickly compared to other areas.

Knowing these types help engineers design structures that are less likely to fail.

Societal Impacts of Corrosion

Corrosion has an important relevance in society aside from being a fascinating chapter in a chemistry textbook.

Corrosion leads to:

• deterioration of structures such as bridges and buildings,
• destruction of transport like vehicles and machinery,
• leaks of pipeline systems,
• interruptions to electrial systems,
• increased costs of upkeep.

Over the years, countless billions of dollars in developed countries have been spent on the:

• maintenance of decaying infrastructure,
• replacement of parts that corroded, and
• development of methods to better control corrosion.

This gives an indication of the extent to which it is necessary to manage corrosion.

Controlling Corrosion

Corrosion is a process that can be controlled but not stopped.

It is Alway present in the environment and its process can be controlled by keeping contact between the metal and the surrounding environment.

There are many Corrosion control methods that aim to prevent the flow of corrosive elements to the metal being protected.

Most Common methods include:

Painting:

• It is the most common method of corrosion control by creating a physical barrier between metal and oxygen
• It is often used in the protective coating of gates, railings, and bridges.

Oiling and Greasing:

• This method is often used in the protective coating of machine parts and tools.
• It is used to keep moisture from coming in contact with the metal.

Galvanization:

• This method is done by coating iron with a thin layer of zinc.
• Before the iron can rust, the zinc will rust first and thus offer protection to the iron.
• It is a common method used in the coating of roofing sheets and buckets.

Electroplating:

• This is a method of coating a metal with a different metal such as chromium or nickel.
• It can offer some aesthetic benefits as well as corrosion resistance.

Mixing metals = alloys

• Stainless steel does not rust because it contains chromium.

Cathodic protection:

• Using a more active metal as a 'sacrificial' anode
• Used in pipeline protection & ship hulls.

Corrosion protection is based on cost, environment and purpose of the metal.

Corrosion and the environment

Corrosion is affected by environmental conditions like rain or snow, and human activity.

Remember these points: Corrosion is increased by rain, and industrial waste in the water

Pollution contains gases that are corrosive and that contribute to acid rain.

Waste and natural resource protection can be achieved by using better materials and protective coatings.

The importance of protecting not only the metal but also the environment can be seen in the application of protective coatings and more structurally efficient designs.

The Importance of Understanding Corrosion

Corrosion is more than just rust on iron, it is chemistry in action. Understanding corrosion allows students to: -See chemistry in action.

• Understand the behavior of materials in the environment.
• Understand the importance of protective measures.
• Develop an appreciation for safety and sustainability.

Corrosion in the MYP helps develop:

• Scientific reasoning.
• Understanding and applying chemical reactions.
• Understanding the relationship between science and society.

Metals are present in all aspects of contemporary society. Studying how they alter, why changes occur, and how we can safeguard metals demonstrates the role of chemistry in advancing civilization.