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Questions and Answers
What is the primary purpose of phosphating in surface treatment?
What is the primary purpose of phosphating in surface treatment?
Which step is NOT part of the phosphating process?
Which step is NOT part of the phosphating process?
What is the purpose of applying a primer before other coatings?
What is the purpose of applying a primer before other coatings?
At what temperature is the phosphating process typically carried out?
At what temperature is the phosphating process typically carried out?
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What characteristic is essential for organic coatings to be effective?
What characteristic is essential for organic coatings to be effective?
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Which materials are mentioned as fillers for improving the external appearance of paint?
Which materials are mentioned as fillers for improving the external appearance of paint?
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What is the purpose of sanding with emery paper after applying fillers?
What is the purpose of sanding with emery paper after applying fillers?
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Which of the following is a widely used accelerator in phosphating baths?
Which of the following is a widely used accelerator in phosphating baths?
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In the sacrificial anode method, which metal is commonly used to protect iron?
In the sacrificial anode method, which metal is commonly used to protect iron?
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What is NOT a requirement of a good organic coating?
What is NOT a requirement of a good organic coating?
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Which of the following sequences is correct for the application of coating?
Which of the following sequences is correct for the application of coating?
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What occurs in the impressed voltage method of cathodic protection?
What occurs in the impressed voltage method of cathodic protection?
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Which of the following methods is NOT used for the application of organic coatings?
Which of the following methods is NOT used for the application of organic coatings?
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What happens during the first step of the phosphating mechanism?
What happens during the first step of the phosphating mechanism?
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What potential risk arises from the breakdown of organic coatings?
What potential risk arises from the breakdown of organic coatings?
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Which metal is considered most resistant to corrosion?
Which metal is considered most resistant to corrosion?
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What occurs during differential metal corrosion?
What occurs during differential metal corrosion?
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What is a disadvantage of using the sacrificial anode method?
What is a disadvantage of using the sacrificial anode method?
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Which of these metals is most anodic or easy to corrode?
Which of these metals is most anodic or easy to corrode?
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Which type of corrosion is caused by different parts of a metal being exposed to varying oxygen concentrations?
Which type of corrosion is caused by different parts of a metal being exposed to varying oxygen concentrations?
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Which metal combination will potentially lead to corrosion of iron?
Which metal combination will potentially lead to corrosion of iron?
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What is the primary process that occurs at the anode during corrosion?
What is the primary process that occurs at the anode during corrosion?
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Which type of corrosion occurs when screws and nuts made of different metals are used together?
Which type of corrosion occurs when screws and nuts made of different metals are used together?
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In the case of rusting of iron, which of the following reactions occurs at the cathode in an aerated neutral medium?
In the case of rusting of iron, which of the following reactions occurs at the cathode in an aerated neutral medium?
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What happens as the potential difference increases between two metals in contact with each other?
What happens as the potential difference increases between two metals in contact with each other?
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Which of the following metals is known to form a passive layer that can resist corrosion?
Which of the following metals is known to form a passive layer that can resist corrosion?
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What determines the risk of galvanic corrosion between two metals?
What determines the risk of galvanic corrosion between two metals?
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Which of the following is NOT a factor affecting corrosion according to electrochemical theory?
Which of the following is NOT a factor affecting corrosion according to electrochemical theory?
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What is the end product of the reaction between Fe2+ and OH- ions formed during iron corrosion?
What is the end product of the reaction between Fe2+ and OH- ions formed during iron corrosion?
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When a medium is deaerated and neutral, what is the principal reaction that takes place?
When a medium is deaerated and neutral, what is the principal reaction that takes place?
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Which statement about the galvanic series is accurate?
Which statement about the galvanic series is accurate?
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Which of the following conditions implies an acidic medium leading to hydrogen formation during corrosion?
Which of the following conditions implies an acidic medium leading to hydrogen formation during corrosion?
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What type of corrosion protection is used by connecting a steel water tank to a magnesium block?
What type of corrosion protection is used by connecting a steel water tank to a magnesium block?
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Which process is exemplified by galvanizing?
Which process is exemplified by galvanizing?
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Which coating method gives a chemical conversion coating?
Which coating method gives a chemical conversion coating?
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What happens to the potential at the anode due to polarization?
What happens to the potential at the anode due to polarization?
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What occurs to the potential at the cathode as a result of polarization?
What occurs to the potential at the cathode as a result of polarization?
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What is the result of electrode polarization on the rate of corrosion?
What is the result of electrode polarization on the rate of corrosion?
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Formation of a protective coating is primarily associated with which processes?
Formation of a protective coating is primarily associated with which processes?
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How is the rate of corrosion affected by high hydrogen overvoltage?
How is the rate of corrosion affected by high hydrogen overvoltage?
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What is the primary purpose of anodic protection in metals like Al, Ti, and Ta?
What is the primary purpose of anodic protection in metals like Al, Ti, and Ta?
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Which material is NOT mentioned as an inert anode for anodic protection?
Which material is NOT mentioned as an inert anode for anodic protection?
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What does the passivating potential (Ep) represent in the context of anodic protection?
What does the passivating potential (Ep) represent in the context of anodic protection?
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What occurs when the anodic current reaches the critical point (icrit)?
What occurs when the anodic current reaches the critical point (icrit)?
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What is the relationship between the passivating current (ip) and the potential above the passivating potential (Ep)?
What is the relationship between the passivating current (ip) and the potential above the passivating potential (Ep)?
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Which component is NOT part of the schematic arrangement for anodic protection?
Which component is NOT part of the schematic arrangement for anodic protection?
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Which aspect is essential for the successful application of anodic protection?
Which aspect is essential for the successful application of anodic protection?
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What happens at point C in the anodic protection process?
What happens at point C in the anodic protection process?
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Study Notes
Corrosion Science
- Corrosion is the destruction or deterioration of metals or alloys by the environment through electrochemical or chemical reactions.
- Examples include rusting of iron and the formation of green scale on copper.
Electrochemical Theory of Corrosion
- When a metal like iron is exposed to the atmosphere, numerous microscopic galvanic cells form on its surface.
- Oxidation occurs at the anode, releasing electrons.
- Reduction occurs at the cathode, accepting electrons.
- Reactions depend on the environment (aerated/de-aerated, neutral/acidic).
- Metal ions from the anode and OH from the cathode react to form metal hydroxides, which further oxidize into metal oxides (corrosion products).
Galvanic Series
- A galvanic series displays the relative nobility of metals and alloys in seawater.
- The further apart materials are in the series, the higher risk of galvanic corrosion.
- Platinum, gold, and graphite are highly resistant to corrosion.
- Copper is less resistant.
Types of Corrosion
- Differential Metal Corrosion: Different metals in contact, the more anodic metal corrodes (e.g., zinc with iron).
- Differential Aeration Corrosion: Different oxygen concentrations on a metal surface. The less aerated part acts as the anode and corrodes (e.g., partially submerged iron).
- Stress Corrosion: Metals under stress corrode faster in specific environments (e.g., stressed iron in alkali, stressed brass in ammonia).
Pitting Corrosion
- Dust on a metal surface creates an area with less aeration, acting as an anode and causing pitting corrosion.
Stress Corrosion
- Stress on a metal (such as bending) can create an anodic region, leading to localized corrosion.
- Factors include the presence of specific corrosive environments.
Factors Affecting Corrosion Rate
- Nature of Corrosion Product: Non-porous, non-conducting, and insoluble products slow down corrosion.
- Electrode Potential: Higher potential difference between metals leads to faster corrosion.
- Anodic and Cathodic Areas: A smaller anodic area with a larger cathodic area results in faster corrosion.
Corrosion Control
- Metal Coatings: Applying anodic (e.g., galvanizing zinc on iron) or cathodic coating (e.g., tinning iron) to protect the base metal.
- Inorganic Coatings: Processes like anodizing (forming a metal oxide layer) and phosphating (applying phosphate layer) improve corrosion resistance.
- Organic Coatings: Applying paint or other organic substances to protect metal surfaces.
- Cathodic Protection: Using an external current source to make the metal the cathode, preventing oxidation.
Corrosion Inhibitors
- Anodic Inhibitors: Oxidizing agents that form a protective coating on the metal's surface (e.g., chromates, molybdates).
- Cathodic Inhibitors: Preventing hydrogen evolution and reducing reactions (e.g., amines, mercaptans).
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Description
Explore the science of corrosion, including its electrochemical basis and the factors influencing metal deterioration. This quiz covers concepts such as galvanic cells, oxidation-reduction reactions, and the galvanic series of metals. Test your understanding of how environmental conditions affect corrosion processes.
