Corrosion and its Prevention - SS2 Chemistry Lesson Note
Corrosion is the deterioration of materials, usually metals, due to chemical reactions with their environment. It is a natural process that can be costly and dangerous, leading to structural failures, equipment damage, and safety hazards. The most common form of corrosion is electrochemical corrosion, which involves the transfer of electrons between the metal and its environment. It occurs in the presence of an electrolyte (e.g., moisture, acids, or salts) and results in the formation of unwanted compounds, such as oxides, hydroxides, or sulphides. Factors contributing to corrosion include moisture, oxygen, temperature, pH, pollutants, and the presence of corrosive agents such as acids, salts, or gases.
Types of Corrosion:
a. Uniform corrosion: Occurs uniformly over the entire surface of the metal, resulting in a general thinning or dissolution of the metal.
b. Galvanic corrosion: Occurs when two dissimilar metals or alloys come in contact in the presence of an electrolyte, leading to accelerated corrosion of the less noble (more reactive) metal.
c. Pitting corrosion: Localised corrosion is characterised by the formation of small pits or holes on the metal surface.
d. Crevice corrosion: Occurs in confined spaces or crevices where the supply of oxygen or other reactants is limited.
e. Intergranular corrosion: Occurs along the grain boundaries of metal, often due to impurities or alloying elements that affect the grain boundaries' stability.
f. Stress corrosion cracking: A form of corrosion that occurs under the combined action of tensile stress and a corrosive environment, leading to the brittle fracture of the metal.
Methods of Corrosion Prevention:
a. Protective coatings: Application of coatings such as paints, enamels, or polymer films on the metal surface to act as a barrier, preventing direct contact with corrosive agents.
b. Cathodic protection: Involves making the metal to be protected by the cathode of an electrochemical cell, either through sacrificial anodes (more reactive metals that corrode preferentially) or impressed current systems.
c. Alloying: Adding specific elements to the base metal to form alloys that are more resistant to corrosion.
d. Use of inhibitors: Addition of chemical inhibitors that form a protective film on the metal surface, reducing the corrosion rate.
e. Design considerations: Modifying the design of structures or equipment to minimise areas prone to corrosion, such as avoiding stagnant or confined spaces.
f. Environmental control: Limiting exposure to moisture, controlling temperature and humidity levels, and managing chemical concentrations in the environment.
g. Proper maintenance and cleaning: Regular inspection, cleaning, and removal of deposits or contaminants that can accelerate corrosion.
Corrosion prevention strategies depend on the specific material, environment, and application. A combination of multiple methods may be employed to provide effective protection. Understanding the causes and prevention of corrosion is crucial in various industries, including infrastructure, manufacturing, transportation, oil and gas, marine, and electronics.
Efficient corrosion prevention measures help extend the lifespan of materials, improve safety, reduce maintenance costs, and ensure the integrity of structures and equipment. Continuous research and development in corrosion-resistant materials and technologies play a vital role in mitigating the impact of corrosion on various industries.