A collapsing bridge or a rusted car frame shows how corrosion silently damages the structures we depend on every day. Corrosion is a natural process where metals react with their environment, leading to material deterioration. It’s all around us, weakening buildings, vehicles, and pipelines—often unnoticed until failure occurs.
This online chemistry textbook explains corrosion in detail, from its causes and types to effective prevention techniques. You’ll learn about processes like galvanic corrosion, the effects of environmental factors, and practical ways to protect materials. Real-life examples help connect the science of corrosion to everyday situations.
Corrosion: Quick Summary
Do you just need the basics? Here’s a simple explanation of what is a corrosion:
🟠 Corrosion occurs when metals deteriorate through chemical or electrochemical reactions with their surroundings, forming compounds like oxides or salts.
🟠 Types of corrosion include general attack, localized damage like pitting and crevice corrosion, and galvanic corrosion, where one metal corrodes faster in contact with another in an electrolyte.
🟠 Environmental factors such as humidity, salt exposure, and temperature can increase corrosion rates, while protective coatings and treatments help reduce damage.
🟠 Non-metallic materials, including polymers, ceramics, and glass, can degrade through processes like ozone cracking in rubber and chemical reactions with corrosive substances.
🟠 Preventing corrosion involves methods like surface treatments, cathodic protection, and using corrosion-resistant materials such as stainless steel, aluminum, and titanium.
What is Corrosion?
Corrosion happens when metals deteriorate due to chemical or electrochemical reactions with their environment. This process often involves oxidation, where metals lose electrons and form compounds like oxides or salts. For example, iron reacts with oxygen and moisture to produce rust, while copper develops a green patina over time.
Materials other than metals can also degrade. Rubber can crack due to ozone exposure, and glass may weaken in harsh chemical conditions. While these processes are not strictly corrosion, they share similarities in material breakdown.
Common examples of corrosion:
- Rust forming on steel
- Patina on copper surfaces
- Pitting on aluminum
- Tarnish on silver
Table: Corrosion Rates of Common Metals
| Metal | Corrosion Rate (mm/year) | Common Form | Resistance |
| Iron (Steel) | High | Rust (iron oxide) | Low |
| Copper | Moderate | Patina (copper oxide) | Moderate |
| Aluminum | Low | Pitting corrosion | High |
| Stainless Steel | Very Low | Localized corrosion (rare) | Very High |
Corrosion affects metals differently, depending on their properties and environment. Knowing how these reactions occur helps explain why certain materials last longer than others.
Types of Corrosion
Corrosion occurs in different ways, depending on the material and its environment. Some types affect entire surfaces, while others damage specific areas, often leading to unexpected failures. Here’s an overview of the most common types.
General Attack Corrosion
General attack corrosion happens when the entire surface of a metal reacts uniformly with its environment. For example, steel exposed to air and moisture develops rust across its surface. This type is predictable and often manageable but can still weaken materials if left untreated.
Localized Corrosion
Localized corrosion damages small, specific areas and is harder to detect.
- Pitting: Tiny, deep holes form when protective coatings fail.
- Crevice Corrosion Happens in tight spaces like under gaskets, where oxygen levels vary.
- Filiform Corrosion: Corrosion spreads in thread-like patterns under coatings, often caused by trapped moisture.
These forms can compromise structural integrity before visible signs appear.
Galvanic Corrosion
Galvanic corrosion occurs when two different metals come into contact in an electrolyte, such as saltwater. The more reactive metal (anode) corrodes faster, protecting the less reactive one (cathode). For example, zinc often serves as a sacrificial anode to shield steel in marine environments.
Common Examples of Corrosion Types:
- General Attack: Uniform rusting of steel.
- Pitting: Holes in aluminum.
- Crevice: Damage underseals or joints in stainless steel.
- Filiform: Corrosion under painted surfaces.
- Galvanic: Zinc protecting steel in seawater.
Each type affects materials differently, requiring specific prevention techniques.
Factors Affecting Corrosion
Corrosion depends on environmental conditions and the material itself. Humidity, temperature, and salinity often speed up corrosion. In humid air, metals react with moisture, forming oxides. Salt in coastal or marine environments accelerates this process, especially for materials like steel. High temperatures increase the speed of chemical reactions, making corrosion happen faster.
The type of material also matters. Metals like stainless steel and aluminum resist corrosion better because they form protective oxide layers. In contrast, untreated steel quickly corrodes unless you apply protective coatings like paint, galvanization, or anodizing. Imperfections in these coatings, such as scratches, leave the metal exposed and vulnerable.
Environmental Factors That Increase Corrosion:
- High humidity
- Salt in the air near oceans
- High or fluctuating temperatures
- Acidic pollutants, including acid rain
Material-Specific Factors That Affect Corrosion:
- Resistance of the metal
- Quality and uniformity of coatings
- Surface conditions, such as scratches or wear
Table: Environmental Conditions and Corrosion Rates
| Environment | Corrosion Rate | Example |
| Dry air | Very Low | Stored tools or equipment |
| Humid air | Moderate | Outdoor steel furniture |
| Marine (salt exposure) | High | Corrosion on ships and bridges |
| Industrial (acid pollutants) | High | Damage to metal structures |
You can reduce corrosion by choosing materials suited to the environment and applying protective coatings. For example, stainless steel performs better in marine settings due to its natural resistance.
Methods for Preventing Corrosion
You can prevent corrosion by protecting materials from their environment. Effective methods include surface treatments, cathodic protection, and selecting the right materials for specific conditions.
Surface Treatments
Surface treatments create barriers that block moisture, oxygen, and corrosive substances from reaching the metal.
- Painting: Paint forms a protective layer, keeping moisture out. Bridges, for example, are painted with durable coatings to withstand rain, wind, and pollution.
- Plating: Metals like chromium or nickel are applied as thin layers over the base material. Chrome plating, often used on car parts, provides both protection and a polished finish.
- Galvanization: Steel is coated with zinc, which corrodes before the steel does. Even if scratched, the zinc protects the steel. This makes galvanized steel ideal for fences and roofing.
Cathodic Protection
Cathodic protection changes how corrosion occurs, sacrificing a more reactive material or using electricity to control reactions.
- Sacrificial Anodes: A reactive metal, such as zinc or magnesium, is attached to the structure. It corrodes in place of the main material, commonly protecting ships, pipelines, and underground tanks.
- Impressed Current Systems: An electric current forces the metal to act as a cathode, preventing it from corroding. Large structures like bridges and storage tanks often use this method.
Material Selection
Choosing materials that resist corrosion naturally can reduce maintenance and extend the lifespan of structures. Stainless steel, aluminum, and titanium form protective oxide layers that shield them from damage. Copper alloys, such as bronze, resist corrosion in harsh conditions, making them suitable for marine environments.
Common Corrosion-Resistant Materials:
- Stainless steel
- Aluminum
- Titanium
- Copper alloys (bronze, brass)
- Nickel-based alloys
Selecting the right combination of treatments and materials depends on the environment. For example, galvanized steel works well for outdoor structures, while stainless steel performs better in salty or humid areas. Combining these methods provides the best protection and helps avoid costly repairs or replacements later.
Testing and Measuring Corrosion Rates
Testing corrosion rates helps you evaluate material durability and plan maintenance effectively.
The weight-loss test is one of the simplest methods. A metal sample is weighed, exposed to a corrosive environment, and weighed again. The weight difference shows how much material was lost due to corrosion. Another widely used method is electrochemical testing, which measures electrical currents generated during corrosion reactions to determine the rate. These techniques provide data for choosing materials and designing protective strategies.
Table: Corrosion Testing Methods and Their Applications
| Method | How It Works | Applications |
| Weight-loss test | Measures reduction in material weight | Studying general corrosion patterns |
| Electrochemical testing | Tracks electrical currents | Assessing corrosion in metals under specific conditions |
| Visual inspection | Identifies visible signs of damage | Routine checks during maintenance |
Real-Life Impacts of Corrosion
Corrosion has caused major failures in infrastructure, leading to severe consequences. The collapse of a suspension bridge due to a single corroded chain highlighted how unnoticed corrosion can result in loss of life. Similarly, pipeline failures caused by corrosion have led to environmental damage, disrupted services, and costly repairs.
Corrosion also shortens the lifespan of structures like bridges, buildings, and pipelines. Rusted steel and weakened concrete require frequent repairs, increasing costs and creating safety risks. For example, corroded steel reinforcement in bridges weakens their stability and demands expensive restoration to prevent failures.
The economic impact of corrosion is enormous. Industries spend vast amounts each year on maintenance, repairs, and replacements caused by corrosion. Sectors such as transportation, utilities, and production face significant expenses due to downtime and damaged infrastructure. Replacing corroded water pipes, for instance, costs billions and affects everyday life.
Corrosion is more than material damage—it impacts safety, infrastructure reliability, and budgets. Effective prevention and maintenance reduce failures and help maintain stable and durable structures over time.
Corrosion in Non-Metallic Materials
Corrosion isn’t limited to metals. Polymers, ceramics, and glass can also degrade, though the processes differ.
Polymers can undergo degradation when exposed to harsh environments. For instance, ozone cracking in rubber occurs when rubber reacts with ozone, leading to cracks and loss of flexibility. Plastic materials may also swell or become brittle due to exposure to chemicals or ultraviolet light.
Ceramics, while generally resistant, can corrode in extreme conditions. For example, chemical reactions with acidic or alkaline solutions can slowly dissolve ceramic components.
Glass, though durable, is not immune to damage. Chemical corrosion in glass occurs when it comes into contact with highly reactive substances, weakening the structure over time. This is commonly observed in industrial or laboratory settings.
Non-metallic materials, like metals, require proper care to maintain their durability.
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Corrosion: Frequently Asked Questions
1. What is corrosion?
Corrosion happens when materials, especially metals, break down due to chemical reactions with their surroundings.
2. What causes corrosion?
Factors like moisture, oxygen, salt, and pollutants trigger corrosion by reacting with the material’s surface.
3. What are the types of corrosion?
The most common types are general attack, pitting, crevice corrosion, and galvanic corrosion between metals.
4. How does galvanic corrosion occur?
Galvanic corrosion occurs when two different metals touch in an electrolyte, causing one to corrode faster.
5. How can corrosion be prevented?
You can prevent corrosion with protective coatings, cathodic protection, or by using corrosion-resistant materials.
6. Can non-metallic materials experience corrosion?
Yes, materials like polymers, ceramics, and glass degrade through processes like cracking or chemical reactions.
7. Why is stainless steel resistant to corrosion?
Stainless steel forms a thin oxide layer that protects it from reacting with moisture or oxygen.
8. What materials resist corrosion best?
Stainless steel, aluminum, titanium, and copper alloys resist corrosion because of their natural or treated surfaces.
Sources:
1. LibreTexts Chemistry
2. Britannica
3. Wikipedia
