Podcast
Questions and Answers
What is the primary purpose of phosphating in surface treatment?
What is the primary purpose of phosphating in surface treatment?
- To alter the color of the metal surface
- To increase the thickness of the metal
- To improve corrosion resistance and paint adhesion (correct)
- To enhance the electrical conductivity of the metal
Which step is NOT part of the phosphating process?
Which step is NOT part of the phosphating process?
- Dissolution of the metal as metal ions
- Formation of metal phosphates
- Deposition of metal phosphate on the surface
- Painting the surface immediately (correct)
What is the purpose of applying a primer before other coatings?
What is the purpose of applying a primer before other coatings?
- To protect against chemical damage
- To improve adherence of subsequent paint layers (correct)
- To enhance the color of the final coat
- To provide insulation against electricity
At what temperature is the phosphating process typically carried out?
At what temperature is the phosphating process typically carried out?
What characteristic is essential for organic coatings to be effective?
What characteristic is essential for organic coatings to be effective?
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?
What is the purpose of sanding with emery paper after applying fillers?
What is the purpose of sanding with emery paper after applying fillers?
Which of the following is a widely used accelerator in phosphating baths?
Which of the following is a widely used accelerator in phosphating baths?
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?
What is NOT a requirement of a good organic coating?
What is NOT a requirement of a good organic coating?
Which of the following sequences is correct for the application of coating?
Which of the following sequences is correct for the application of coating?
What occurs in the impressed voltage method of cathodic protection?
What occurs in the impressed voltage method of cathodic protection?
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?
What happens during the first step of the phosphating mechanism?
What happens during the first step of the phosphating mechanism?
What potential risk arises from the breakdown of organic coatings?
What potential risk arises from the breakdown of organic coatings?
Which metal is considered most resistant to corrosion?
Which metal is considered most resistant to corrosion?
What occurs during differential metal corrosion?
What occurs during differential metal corrosion?
What is a disadvantage of using the sacrificial anode method?
What is a disadvantage of using the sacrificial anode method?
Which of these metals is most anodic or easy to corrode?
Which of these metals is most anodic or easy to corrode?
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?
Which metal combination will potentially lead to corrosion of iron?
Which metal combination will potentially lead to corrosion of iron?
What is the primary process that occurs at the anode during corrosion?
What is the primary process that occurs at the anode during corrosion?
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?
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?
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?
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?
What determines the risk of galvanic corrosion between two metals?
What determines the risk of galvanic corrosion between two metals?
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?
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?
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?
Which statement about the galvanic series is accurate?
Which statement about the galvanic series is accurate?
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?
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?
Which process is exemplified by galvanizing?
Which process is exemplified by galvanizing?
Which coating method gives a chemical conversion coating?
Which coating method gives a chemical conversion coating?
What happens to the potential at the anode due to polarization?
What happens to the potential at the anode due to polarization?
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?
What is the result of electrode polarization on the rate of corrosion?
What is the result of electrode polarization on the rate of corrosion?
Formation of a protective coating is primarily associated with which processes?
Formation of a protective coating is primarily associated with which processes?
How is the rate of corrosion affected by high hydrogen overvoltage?
How is the rate of corrosion affected by high hydrogen overvoltage?
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?
Which material is NOT mentioned as an inert anode for anodic protection?
Which material is NOT mentioned as an inert anode for anodic protection?
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?
What occurs when the anodic current reaches the critical point (icrit)?
What occurs when the anodic current reaches the critical point (icrit)?
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)?
Which component is NOT part of the schematic arrangement for anodic protection?
Which component is NOT part of the schematic arrangement for anodic protection?
Which aspect is essential for the successful application of anodic protection?
Which aspect is essential for the successful application of anodic protection?
What happens at point C in the anodic protection process?
What happens at point C in the anodic protection process?
Flashcards
Corrosion
Corrosion
The destruction or deterioration of metals by chemical or electrochemical reactions with the environment.
Electrochemical theory of corrosion
Electrochemical theory of corrosion
Corrosion happens due to an electrochemical reaction between a metal and its surroundings, creating tiny electrochemical cells (batteries) on the metal's surface.
Anodic area
Anodic area
The area on the metal surface where oxidation (loss of electrons) happens
Cathodic area
Cathodic area
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Galvanic corrosion
Galvanic corrosion
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Galvanic series
Galvanic series
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Oxidation
Oxidation
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Reduction
Reduction
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Differential metal corrosion
Differential metal corrosion
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Anode
Anode
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Cathode
Cathode
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Electrochemical series
Electrochemical series
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Differential aeration corrosion
Differential aeration corrosion
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Most noble metal
Most noble metal
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Most anodic metal
Most anodic metal
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Phosphating
Phosphating
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Metal Phosphate Coating Mechanism
Metal Phosphate Coating Mechanism
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Organic Coatings
Organic Coatings
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Organic Coating Requirements
Organic Coating Requirements
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Surface Preparation
Surface Preparation
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Paint Application Sequence
Paint Application Sequence
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Corrosion Prevention Methods
Corrosion Prevention Methods
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Accelerators
Accelerators
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Primer Coating
Primer Coating
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Filler Coating
Filler Coating
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Finishing/Top Coat
Finishing/Top Coat
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Cathodic Protection
Cathodic Protection
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Sacrificial Anode Method
Sacrificial Anode Method
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Impressed Voltage/Current Method
Impressed Voltage/Current Method
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How does Zinc protect Steel in sacrificial anode method?
How does Zinc protect Steel in sacrificial anode method?
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Examples of Cathodic Protection
Examples of Cathodic Protection
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Passivation
Passivation
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Passivating Potential (Ep)
Passivating Potential (Ep)
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Passivating Current (ip)
Passivating Current (ip)
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Flade Potential (Ef)
Flade Potential (Ef)
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Inert Anode
Inert Anode
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Suitable Oxidizing Environment
Suitable Oxidizing Environment
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Potential-Current Curve
Potential-Current Curve
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Sacrificial Anodic Protection
Sacrificial Anodic Protection
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Galvanized
Galvanized
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Chemical Conversion Coating
Chemical Conversion Coating
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Anodizing
Anodizing
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Electrode Polarization
Electrode Polarization
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Hydrogen Overvoltage
Hydrogen Overvoltage
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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.
