Short Answer:
Electrochemical corrosion is a type of corrosion that occurs when a metal reacts with its environment through an electrochemical process. It involves the movement of electrons between two different areas on a metal surface or between two connected metals in the presence of an electrolyte like water or salt solution. This process creates an anode and cathode, where the metal at the anode slowly dissolves and corrodes.
This type of corrosion is very common in daily life, especially in wet or salty environments. Examples include rusting of iron, corrosion in pipelines, marine structures, and battery terminals. Electrochemical corrosion can be controlled using protective coatings, cathodic protection, or by avoiding contact between dissimilar metals in moist conditions.
Detailed Explanation:
Electrochemical corrosion
In the world of materials and mechanical engineering, electrochemical corrosion is one of the most common and harmful types of metal deterioration. It happens due to a chemical reaction combined with the flow of electrical current, which leads to the gradual loss of metal. This process is especially active when metals are exposed to electrolytes like rainwater, seawater, soil moisture, or acid vapors.
Understanding electrochemical corrosion is important because it causes damage to pipelines, vehicles, buildings, ships, and even electronic parts.
How electrochemical corrosion occurs
For electrochemical corrosion to happen, four main conditions must be present:
- Anode (active site)
- The metal area where corrosion starts.
- This part loses electrons and dissolves into ions.
- Cathode (inactive site)
- The metal area where electrons are received.
- No corrosion happens here.
- Electrolyte (conductive fluid)
- A liquid like water, saltwater, or acid that allows ions to move.
- Connects the anode and cathode.
- Electrical path
- A connection (direct or through the metal itself) that allows electrons to flow from anode to cathode.
Once these are present, a small electric circuit is formed, and the metal at the anode starts to corrode.
Electrochemical reactions in corrosion
- At the anode (oxidation reaction):
Metal (M) → Mⁿ⁺ + n e⁻
(Metal atoms lose electrons and become metal ions) - At the cathode (reduction reaction):
O₂ + 2H₂O + 4e⁻ → 4OH⁻
(Oxygen reacts with water and electrons to form hydroxide)
These reactions result in the formation of rust (in iron) or other corrosion products depending on the metal.
Examples of electrochemical corrosion
- Rusting of iron in rainwater or seawater
- Battery terminal corrosion in vehicles
- Corrosion in underground pipelines due to moisture in soil
- Galvanic corrosion between two different metals like zinc and copper in contact with water
- Corrosion in ships and boats due to exposure to seawater
Factors that increase electrochemical corrosion
- Presence of salts or acids (increase electrolyte strength)
- High humidity or wet environment
- Use of dissimilar metals in contact
- Poor surface finish or scratches
- Higher temperature (increases reaction speed)
Methods to prevent electrochemical corrosion
- Coatings and paints
- Prevent moisture and air from reaching the metal surface.
- Cathodic protection
- Use sacrificial anodes or impressed current to stop corrosion at the main structure.
- Material selection
- Use corrosion-resistant metals like stainless steel or apply surface treatments.
- Avoid contact between dissimilar metals
- If unavoidable, use rubber or plastic insulation to separate them.
- Use of inhibitors
- Add chemicals to water systems that slow down electrochemical reactions.
- Drainage and ventilation
- Keep metal surfaces dry to reduce electrolyte contact.
Conclusion
Electrochemical corrosion is a process where a metal corrodes due to chemical reactions and flow of electrical current in the presence of an electrolyte. It involves the formation of anodic and cathodic areas on the metal, leading to loss of metal at the anode. This type of corrosion is common in marine, underground, and moist environments. By understanding its working and applying proper prevention methods like coatings, insulation, and cathodic protection, we can protect metals and extend the life of structures and machines.