Corrosion: Its types and Methods of Prevention
Table of Contents
Examples of Corrosion with Equations:
7. Corrosion of Brass (Copper-Zinc Alloy):
10. Corrosion of Stainless Steel:
Multiple Choice Questions for Practice-1
How to prevent corrosion class 10
2. Modification of Environment:
4. Use of Corrosion Inhibitors:
7. Avoidance of Contact with Corrosive Materials:
Multiple
Choice Questions for Practice-2
Corrosion, a natural chemical process, refers to the gradual degradation or deterioration of materials, typically metals, due to various environmental factors. This phenomenon is a significant concern in numerous industries and infrastructure, leading to structural damage, economic losses, and safety hazards. Here we delve into the concept of corrosion, examine its mechanisms, and provide examples along with equations to illustrate its impact on different materials.
Understanding Corrosion:
Corrosion occurs when metals react with substances in their surrounding environment, leading to the formation of undesirable compounds or alteration of the metal's properties. Factors such as moisture, oxygen, acids, and salts contribute to the corrosion process. The most common type of corrosion is Electrochemical corrosion, where metal ions dissolve into the surrounding electrolyte, accompanied by the release of electrons.
Mechanisms of Corrosion:
1. Uniform Corrosion: This type of corrosion occurs evenly across the surface of a metal, leading to a gradual thinning or loss of material. It often arises from exposure to moisture and oxygen in the atmosphere.
2. Galvanic Corrosion: Galvanic corrosion occurs when two dissimilar metals are in contact in the presence of an electrolyte. The more reactive metal undergoes corrosion while the less reactive metal remains protected.
3. Pitting Corrosion: Pitting corrosion involves localized damage to metal surfaces, characterized by small pits or holes. It occurs in environments with high chloride concentrations, such as seawater.
4. Crevice Corrosion: Crevice corrosion occurs in narrow gaps or crevices where stagnant electrolyte solutions accumulate, leading to localized corrosion and material degradation.
5. Intergranular Corrosion: Intergranular corrosion affects the grain boundaries of metals, often due to impurities or sensitization during processing, leading to the preferential corrosion of grain boundaries.
Examples of Corrosion with Equations:
1. Rust Formation on Iron:
\(4Fe(s) + 3O_2(g) + 6H_2O(l) → 4Fe(OH)_3(s)\)
Iron reacts with oxygen and water to form iron(III) hydroxide, commonly known as rust.
2. Corrosion of Aluminium:
\(4Al(s) + 3O_2(g) → 2Al_2O_3(s)\)
Aluminium undergoes oxidation to form aluminium oxide, which acts as a protective layer against further corrosion.
3. Corrosion of Copper:
\(Cu(s) + O_2(g) + H_2O(l) + CO_2(g) → CuCO_3·Cu(OH)_2(s)\)
Copper reacts with oxygen, water, and carbon dioxide in the atmosphere to form a greenish patina, including copper carbonate and hydroxide compounds.
4. Corrosion of Zinc:
\(Zn(s) + 2H^+(aq) → Zn^{2+}(aq) + H_2(g)\)
Zinc undergoes oxidation in acidic environments, forming zinc ions and hydrogen gas.
5. Corrosion of Silver:
\(4Ag(s) + O_2(g) + 2H_2S(g) → 2Ag_2S(s) + 2H_2O(l)\)
Silver reacts with hydrogen sulphide in the atmosphere to form silver sulphide, a black tarnish on the surface of silver objects.
6. Corrosion of Lead:
\(2Pb(s) + O_2(g) + 2H^+(aq) → 2Pb^{2+}(aq) + 2H_2O(l)\)
Lead undergoes oxidation in acidic environments, resulting in the formation of lead ions and water.
7. Corrosion of Brass (Copper-Zinc Alloy):
\(Cu(s) + 2H_2O(l) + CO_2(g) + 2e^- → CuCO_3·Cu(OH)_2(s) + 2H^+(aq)\)
Copper in brass reacts with carbon dioxide and water to form a greenish patina, similar to copper corrosion.
8. Corrosion of Steel:
\(Fe(s) + 2H_2O(l) + O_2(g) → Fe_2O_3·xH_2O(s)\)
Steel undergoes oxidation in the presence of oxygen and water, forming iron(III) oxide hydrate, commonly known as rust.
9. Corrosion of Magnesium:
\(2Mg(s) + O_2(g) → 2MgO(s)\)
Magnesium reacts with oxygen in the atmosphere to form magnesium oxide, which provides some protection against further corrosion.
10. Corrosion of Stainless Steel:
\(Fe(s) + 2H_2O(l) + O_2(g) → Fe_2O_3(s) + 4H^+(aq) + 4e^-\)
Stainless steel undergoes oxidation in the presence of oxygen and water, forming iron(III) oxide and releasing protons and electrons.
Multiple Choice Questions for Practice-1
Q1.Which factor does not contribute to the corrosion process?
A) Salts
B) Moisture
C) Oxygen
D) Acids
C) Oxygen ✔
Q2. What is the most common type of corrosion that involves the dissolution of metal ions into the surrounding electrolyte?
A) Electrochemical corrosion
B) Thermal corrosion
C) Chemical corrosion
D) Galvanic corrosion
A) Electrochemical corrosion ✔
Q3. Galvanic corrosion occurs when:
A) None of the above
B) Dissimilar metals are in contact in an electrolyte
C) Similar metals are in contact in an electrolyte
D) A metal reacts with oxygen only
B) Dissimilar metals are in contact in an electrolyte ✔
Q4. Which type of corrosion involves damage to metal surfaces in the form of small pits or holes?
A) Pitting corrosion
B) Intergranular corrosion
C) Uniform corrosion
D) Galvanic corrosion
A) Pitting corrosion ✔
Q5. Intergranular corrosion affects:
A) The external environment
B) The entire structure
C) The grain boundaries of metals
D) The surface of the metal
C) The grain boundaries of metals ✔
Q6. What compound is commonly known as rust and is formed during the corrosion of iron?
A) Iron hydroxide
B) Iron carbonate
C) Iron chloride
D) Iron oxide
A) Iron hydroxide ✔
Q7. The corrosion of aluminium results in the formation of:
A) Aluminium nitrate
B) Aluminium hydroxide
C) Aluminium chloride
D) Aluminium oxide
D) Aluminium oxide ✔
Q8. Copper corrosion in the atmosphere results in the formation of a greenish patina composed of:
A) Copper sulphide
B) Copper chloride
C) Copper oxide
D) Copper hydroxide
E) Copper carbonate
D) Copper hydroxide ✔
Q9. Which metal reacts with hydrogen sulphide to form a black tarnish on its surface?
A) Gold
B) Palladium
C) Silver
D) Platinum
C) Silver ✔
Q10. Stainless steel undergoes oxidation to form which compound in the presence of oxygen and water?
A) Iron chloride
B) Iron sulphate
C) Iron hydroxide
D) Iron(III) oxide
D) Iron(III) oxide ✔
How to prevent corrosion class 10
Preventing corrosion involves various methods that can be categorized into several approaches. Here are some methods to prevent corrosion:
1. Barrier Protection:
- Painting: Applying paint or coating acts as a physical barrier between the metal surface and corrosive agents in the environment.
- Galvanization: Coating iron or steel with a layer of zinc helps prevent corrosion by sacrificial protection (zinc corrodes preferentially).
2. Modification of Environment:
- Control Humidity: Keep the environment dry or use dehumidifiers to prevent moisture accumulation, which accelerates corrosion.
- Control pH: Ensure the pH of the environment or the material in contact with the metal does not promote corrosion.
3. Cathodic Protection:
- Sacrificial Anode: Placing a more reactive metal (like zinc or magnesium) near the metal to be protected. This sacrificial metal corrodes instead of the protected metal.
- Impressed Current: Using an external electric current to create a protective electrochemical reaction on the surface of the metal.
4. Use of Corrosion Inhibitors:
- Chemical Inhibitors: Adding chemicals that form a protective film on the metal surface, preventing corrosive agents from reaching the metal.
5. Design Considerations:
- Material Selection: Choosing metals or alloys that are more resistant to corrosion in specific environments.
- Proper Drainage: Designing structures to allow easy drainage of water and moisture.
6. Regular Maintenance:
- Cleaning: Regularly clean metal surfaces to remove accumulated dirt, salts, or other substances that can accelerate corrosion.
- Inspection: Periodically inspect metal surfaces for signs of corrosion and take preventive measures promptly.
7. Avoidance of Contact with Corrosive Materials:
- Isolation: Ensure metals are not in direct contact with substances that can accelerate corrosion, such as acids, salts, or harsh chemicals.
These methods can be applied individually or in combination depending on the specific circumstances and the type of metal being protected. Choosing the appropriate method often requires consideration of factors such as cost, environmental conditions, and the expected lifespan of the metal structure or component.
Multiple Choice Questions for Practice-2
Q11. Which method of preventing corrosion involves applying paint or coating as a physical barrier between the metal surface and corrosive agents?
A) Regular Maintenance
B) Use of Corrosion Inhibitors
C) Cathodic Protection
D) Barrier Protection
D) Barrier Protection ✔
Q12. Galvanization involves coating iron or steel with a layer of which metal to prevent corrosion by sacrificial protection?
A) Copper
B) Silver
C) Zinc
D) Aluminium
C) Zinc ✔
Q13. What method of preventing corrosion involves controlling humidity and pH in the environment to hinder moisture accumulation?
A) Barrier Protection
B) Design Considerations
C) Use of Corrosion Inhibitors
D) Modification of Environment
D) Modification of Environment ✔
Q14. Sacrificial Anode is a method of corrosion prevention that involves placing which type of metal near the metal to be protected?
A) Lead
B) Nickel
C) Copper
D) Magnesium
D) Magnesium ✔
Q15. Corrosion inhibitors work by adding chemicals to the metal surface that form a protective film to prevent corrosive agents from reaching the metal. What is the method is this known as?
A) Metal Alloying
B) Chemical Inhibitors
C) Passivation
D) Oxidation
B) Chemical Inhibitors ✔
Q16. Which method of preventing corrosion involves using an external electric current to create a protective electrochemical reaction on the metal surface?
A) Modification of Environment
B) Barrier Protection
C) Cathodic Protection
D) Use of Corrosion Inhibitors
C) Cathodic Protection ✔
Q17. Proper drainage is a design consideration for preventing corrosion. Why is proper drainage important?
A) To prevent easy access for inspection
B) To allow easy drainage of water and moisture
C) To encourage accumulation of dirt and salts
D) To trap moisture and corrosive agents
B) To allow easy drainage of water and moisture ✔
Q18. Keeping the environment dry or using dehumidifiers to prevent moisture accumulation is an example of which method of preventing corrosion?
A) Modification of Environment
B) Barrier Protection
C) Cathodic Protection
D) Use of Corrosion Inhibitors
A) Modification of Environment ✔
Q19. Periodically inspecting metal surfaces for signs of corrosion and taking preventive measures promptly is part of which method of preventing corrosion?
A) Cathodic Protection
B) Use of Corrosion Inhibitors
C) Barrier Protection
D) Regular Maintenance
D) Regular Maintenance ✔
Q20. Choosing metals or alloys that are more resistant to corrosion in specific environments is a design consideration for preventing corrosion. What is this method known as?
A) Sacrificial Anode
B) Galvanization
C) Material Selection
D) Chemical Inhibitors
C) Material Selection ✔
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