Podcast
Questions and Answers
What is the primary cause of corrosion in metals?
What is the primary cause of corrosion in metals?
- Direct exposure to water
- Physical wear and tear
- High temperatures only
- Chemical or electrochemical attack from the environment (correct)
Which metals are known to corrode to a negligible extent?
Which metals are known to corrode to a negligible extent?
- Chromium and tungsten
- Iron and copper
- Silver and gold (correct)
- Sodium and calcium
What is a key factor that influences the rate of dry corrosion?
What is a key factor that influences the rate of dry corrosion?
- The color of the metal
- The weight of the metal
- The affinity between metals and the environment (correct)
- The presence of water vapor
What happens to metals in their natural state that leads to corrosion?
What happens to metals in their natural state that leads to corrosion?
Which type of corrosion results from a direct chemical attack from dry gases or anhydrous liquids?
Which type of corrosion results from a direct chemical attack from dry gases or anhydrous liquids?
What effect does increasing temperature have on the rate of corrosion?
What effect does increasing temperature have on the rate of corrosion?
What type of corrosion involves reactions between metals and moisture?
What type of corrosion involves reactions between metals and moisture?
What characteristic of stable oxides prevents the corrosion of heavy metals?
What characteristic of stable oxides prevents the corrosion of heavy metals?
Which type of oxide layer is likely to result in continued corrosion until the metal is completely oxidized?
Which type of oxide layer is likely to result in continued corrosion until the metal is completely oxidized?
Which phenomenon occurs when atomic hydrogen diffuses into a metal and affects its strength?
Which phenomenon occurs when atomic hydrogen diffuses into a metal and affects its strength?
What type of corrosion occurs when anhydrous liquids attack metal surfaces?
What type of corrosion occurs when anhydrous liquids attack metal surfaces?
During electrochemical corrosion, what happens at the anodic area?
During electrochemical corrosion, what happens at the anodic area?
Which factor influences the rate of corrosion by dry gases?
Which factor influences the rate of corrosion by dry gases?
What type of oxide is characterized by its ability to rapidly evaporate once formed?
What type of oxide is characterized by its ability to rapidly evaporate once formed?
In which reaction does oxidation occur at the anode, while reduction takes place at the cathode?
In which reaction does oxidation occur at the anode, while reduction takes place at the cathode?
What happens to metals when they form unstable oxides?
What happens to metals when they form unstable oxides?
What is the primary purpose of using a sacrificial anode in cathodic protection?
What is the primary purpose of using a sacrificial anode in cathodic protection?
Which of the following processes is involved in galvanizing iron or steel?
Which of the following processes is involved in galvanizing iron or steel?
What is the main difference between primary batteries and secondary batteries?
What is the main difference between primary batteries and secondary batteries?
What should be avoided in the design of equipment to prevent localized corrosion?
What should be avoided in the design of equipment to prevent localized corrosion?
In the impressed current method of cathodic protection, what is typically used as the rectifying element?
In the impressed current method of cathodic protection, what is typically used as the rectifying element?
What occurs at the anode during the Hydrogen Evolution Mechanism of corrosion?
What occurs at the anode during the Hydrogen Evolution Mechanism of corrosion?
In which type of corrosion does H2 gas evolve at the cathode?
In which type of corrosion does H2 gas evolve at the cathode?
What occurs at the anode during galvanic corrosion?
What occurs at the anode during galvanic corrosion?
What is the primary product formed when ferrous hydroxide is oxidized in the presence of enough oxygen?
What is the primary product formed when ferrous hydroxide is oxidized in the presence of enough oxygen?
Which type of corrosion results from a difference in aeration levels in a stagnant water environment?
Which type of corrosion results from a difference in aeration levels in a stagnant water environment?
Which condition is necessary for stress corrosion to occur?
Which condition is necessary for stress corrosion to occur?
Under which condition does inter-granular corrosion primarily occur?
Under which condition does inter-granular corrosion primarily occur?
What is a primary factor affecting corrosion resistance in metals?
What is a primary factor affecting corrosion resistance in metals?
Which process intensifies corrosion for metals like mild steel in alkaline solutions?
Which process intensifies corrosion for metals like mild steel in alkaline solutions?
Which reaction occurs at the cathode during the Oxygen Absorption Mechanism?
Which reaction occurs at the cathode during the Oxygen Absorption Mechanism?
What is a common control method for preventing pitting corrosion?
What is a common control method for preventing pitting corrosion?
According to the Pilling Bedworth rule, what determines if an oxide layer is protective?
According to the Pilling Bedworth rule, what determines if an oxide layer is protective?
What leads to the formation of pits in metals during pitting corrosion?
What leads to the formation of pits in metals during pitting corrosion?
What alloying component in copper can lead to season cracking in the presence of ammonia?
What alloying component in copper can lead to season cracking in the presence of ammonia?
Why does oxygen absorption corrosion typically have a small anodic area?
Why does oxygen absorption corrosion typically have a small anodic area?
What role does cathodic protection play in corrosion control?
What role does cathodic protection play in corrosion control?
What happens to Fe2+ ions and hydroxide ions during the oxidation reaction in the Oxygen Absorption Mechanism?
What happens to Fe2+ ions and hydroxide ions during the oxidation reaction in the Oxygen Absorption Mechanism?
What happens to the corrosion rate when a metal's internal stress is reduced through proper heat treatment?
What happens to the corrosion rate when a metal's internal stress is reduced through proper heat treatment?
Which combination fosters corrosion when using dissimilar metals in construction?
Which combination fosters corrosion when using dissimilar metals in construction?
Which environment can cause stress corrosion specifically in mild steel?
Which environment can cause stress corrosion specifically in mild steel?
What is the main reason metals corrode when extracted from their ores?
What is the main reason metals corrode when extracted from their ores?
Which factor is NOT mentioned as influencing dry corrosion?
Which factor is NOT mentioned as influencing dry corrosion?
Which type of corrosion involves a direct chemical attack from gases or anhydrous liquids?
Which type of corrosion involves a direct chemical attack from gases or anhydrous liquids?
What effect does the formation of volatile corrosion products have on the rate of corrosion?
What effect does the formation of volatile corrosion products have on the rate of corrosion?
What happens to metals with high chemical affinity towards their environmental factors?
What happens to metals with high chemical affinity towards their environmental factors?
In the context of corrosion, what is the definition of wet corrosion?
In the context of corrosion, what is the definition of wet corrosion?
Which metals are known to corrode to a considerable extent?
Which metals are known to corrode to a considerable extent?
What is the purpose of not completely coating anodic metals with protective coatings?
What is the purpose of not completely coating anodic metals with protective coatings?
Which method of cathodic protection uses a more active metal to protect a metallic structure?
Which method of cathodic protection uses a more active metal to protect a metallic structure?
What are the two methods of cathodic protection outlined in the information?
What are the two methods of cathodic protection outlined in the information?
What chemical process is primarily involved in battery operation?
What chemical process is primarily involved in battery operation?
Which type of battery consists of irreversible electrode reactions?
Which type of battery consists of irreversible electrode reactions?
What occurs at the anode during galvanic corrosion?
What occurs at the anode during galvanic corrosion?
What is the primary cause of stress corrosion?
What is the primary cause of stress corrosion?
What gas is evolved at the cathode during the Hydrogen Evolution Mechanism of corrosion?
What gas is evolved at the cathode during the Hydrogen Evolution Mechanism of corrosion?
Which type of oxide layer is most effective at preventing further corrosion?
Which type of oxide layer is most effective at preventing further corrosion?
What is a common method to improve a metal's corrosion resistance?
What is a common method to improve a metal's corrosion resistance?
What type of corrosion occurs when oxygen gas is absorbed at the cathode?
What type of corrosion occurs when oxygen gas is absorbed at the cathode?
Which type of corrosion primarily involves localized attack in the form of pits?
Which type of corrosion primarily involves localized attack in the form of pits?
What happens to the metal at the cathodic area during galvanic corrosion?
What happens to the metal at the cathodic area during galvanic corrosion?
What is season cracking primarily associated with?
What is season cracking primarily associated with?
In waterline corrosion, which part of the metal acts as the anode?
In waterline corrosion, which part of the metal acts as the anode?
What reaction occurs at the anode during the oxidation process in electrochemical corrosion?
What reaction occurs at the anode during the oxidation process in electrochemical corrosion?
Which factor primarily influences the state of corrosion resistance in alloyed metals?
Which factor primarily influences the state of corrosion resistance in alloyed metals?
What primarily causes inter-granular corrosion?
What primarily causes inter-granular corrosion?
According to the Pilling Bedworth rule, what characterizes a protective oxide layer?
According to the Pilling Bedworth rule, what characterizes a protective oxide layer?
Which control method can help prevent pitting corrosion?
Which control method can help prevent pitting corrosion?
Which combination of conditions is most likely to foster stress corrosion in metals?
Which combination of conditions is most likely to foster stress corrosion in metals?
What is the end product when enough oxygen is present during the oxidation of ferrous hydroxide?
What is the end product when enough oxygen is present during the oxidation of ferrous hydroxide?
What is cathodic protection primarily used for?
What is cathodic protection primarily used for?
How can waterline corrosion be controlled?
How can waterline corrosion be controlled?
Which mechanism primarily leads to hydrogen gas evolution at the cathode?
Which mechanism primarily leads to hydrogen gas evolution at the cathode?
What characteristic of stable oxides helps protect heavy metals from corrosion?
What characteristic of stable oxides helps protect heavy metals from corrosion?
What type of oxide layer is likely to cause continued corrosion due to its porous structure?
What type of oxide layer is likely to cause continued corrosion due to its porous structure?
What occurs during the process of hydrogen embrittlement?
What occurs during the process of hydrogen embrittlement?
Which type of corrosion is characterized by the presence of anodic and cathodic areas in the presence of an electrolyte?
Which type of corrosion is characterized by the presence of anodic and cathodic areas in the presence of an electrolyte?
What is a common characteristic of volatile oxides?
What is a common characteristic of volatile oxides?
What is a potential consequence of corrosion by anhydrous liquids?
What is a potential consequence of corrosion by anhydrous liquids?
In wet or electrochemical corrosion, what occurs at the cathodic area?
In wet or electrochemical corrosion, what occurs at the cathodic area?
Which type of oxide forms an unstable layer that can decompose back into the metal?
Which type of oxide forms an unstable layer that can decompose back into the metal?
What was a consequence observed when chlorination attacks tin?
What was a consequence observed when chlorination attacks tin?
Study Notes
Corrosion Overview
- Corrosion refers to the deterioration of metallic materials due to chemical or electrochemical reactions with the environment.
- Common examples include rusting of iron and the formation of green patina on copper.
- The rate of corrosion varies with the type of metal and environmental conditions.
- Noble metals like gold and silver corrode negligibly, while reactive metals like sodium and calcium corrode extensively.
Causes of Corrosion
- Metals are found in combined states as ores, typically in positive oxidation states, which is their stable form.
- Upon extraction, metals transition to a neutral state, becoming unstable and prone to reacting with environmental factors.
Types of Corrosion
- Corrosion can be classified into two main types: dry (chemical) corrosion and wet (electrochemical) corrosion.
Dry Corrosion
- Involves direct chemical attack by dry gases or anhydrous liquids.
- The rate of dry corrosion is influenced by:
- Chemical Affinity: Higher affinity leads to increased corrosion.
- Temperature: Higher temperatures accelerate corrosion.
- Corrosion Products: Volatile and porous products increase corrosion rates.
Mechanisms of Dry Corrosion
-
Oxidation Corrosion: Occurs when metals react with oxygen.
- Stable Oxides: Form protective layers (e.g., aluminum, copper).
- Porous Oxides: Allow continued corrosion if cracks are present.
- Unstable Oxides: Decompose, preventing sustained oxidation (e.g., silver).
- Volatile Oxides: Facilitate rapid corrosion by volatilizing and exposing fresh metal (e.g., MoO3).
-
Corrosion by Other Gases: Direct attack by gases like Cl2 or H2S accelerates corrosion depending on gas-metal affinity.
-
Hydrogen Corrosion: Atomic hydrogen can diffuse into metals, causing embrittlement and potential intergranular cracking.
-
Corrosion by Anhydrous Liquids: Attack by organic and inorganic liquids that can dissolve or penetrate metal surfaces, depending on temperature gradients.
Wet Corrosion
- Involves contact with electrolytes, creating anodic and cathodic areas for current flow.
- Anodic areas experience oxidation, while cathodic areas undergo reduction.
Types of Wet Corrosion Mechanisms
- Galvanic Corrosion: Occurs between dissimilar metals in an electrolyte, with the less noble metal corroding.
- Concentration Cell Corrosion: Differences in the concentration of ions can generate localized corrosion.
Specific Types of Corrosion
- Pitting Corrosion: Localized corrosion forming small pits, accelerated by aeration differences.
- Waterline Corrosion: Occurs in stagnant water, with oxygen-rich areas acting as cathodes.
- Intergranular Corrosion: Targets grain boundaries, influenced by impurities and environmental factors.
- Stress Corrosion: Results from tensile stress in conjunction with specific corrosive agents, leading to localized corrosion.
Corrosion Control Methods
-
Material Selection:
- Use metals with high corrosion resistance and purity.
- Alloying improves resistance.
-
Design Considerations:
- Ensure uniform stability in design.
- Avoid contact between dissimilar metals.
-
Cathodic Protection: Employ sacrificial anodes or impressed current to reduce the metal potential.
-
Protective Surface Coatings: Utilize paint or other coatings to shield metal from environmental exposure.
Key Principles
- Pilling Bedworth Rule: Protective oxides should have a volume greater than the metal volume to prevent continued corrosion. Porous oxides permit corrosion progression.
- Understanding these principles and corrosion mechanisms is essential for effective corrosion management in various applications.### Corrosion Prevention of Dissimilar Metals
- Anodic material should have a larger surface area compared to the cathodic metal to reduce corrosion rates.
- Coatings with insulating materials are critical to prevent direct contact between dissimilar metals.
- Anodic metal should not be fully coated to avoid rapid pitting if any breaks occur in the protective layer.
- Effective equipment design should minimize accumulation of corrosive materials and avoid sharp bends or localized stresses.
- Tanks and pipelines must be designed to eliminate obstructions and crevices.
Cathodic Protection Methods
- Cathodic protection forces a metal structure to act as a cathode using opposite external current to prevent corrosion.
- Sacrificial Anode Method: Involves connecting the metallic structure to a more active metal, which corrodes instead of the protected metal.
- Common sacrificial anodes include zinc, magnesium, and aluminum.
- Needs periodic replacement once the sacrificial anode is consumed.
- Impressed Current Method: Applies a current to counteract corrosion current, converting the corroding metal to a cathode.
- Utilizes a direct current source, such as a battery or rectifier.
- Anodes are often buried in conductive backfill to enhance soil contact.
- Suitable for large structures and offers reduced maintenance and operating costs.
Protective Surface Coatings
- Galvanizing: Coats iron or steel with zinc to prevent rusting.
- Involves cleaning steel with dilute sulfuric acid followed by dipping in molten zinc at 425-430°C.
- A flux of ammonium chloride prevents oxide formation during the process.
- Commonly used for roofing sheets, pipes, and containers.
- Tinning: Coats steel, copper, or brass with tin.
- Steel is first treated with diluted sulfuric acid, then passes through zinc chloride flux, followed by molten tin.
- The tin-coated surface is protected by palm oil during processing.
Battery Technology
- Batteries convert chemical energy to electrical energy through redox reactions involving oxidation and reduction.
- A battery comprises multiple electrochemical cells which consist of anodes, cathodes, and electrolytes.
- Terminal voltage is measured across battery terminals; open circuit voltage is the EMF when not under load.
Types of Batteries
- Primary Batteries: Non-rechargeable; electrode reactions are irreversible.
- Secondary Batteries: Rechargeable, allowing reversible electrode reactions.
Nickel-Cadmium (Ni-Cd) Battery
- First sealed rechargeable battery, exhibiting long cycle life and good performance even at low temperatures.
- Construction features a jelly-roll design with a sealed metal case, including separators for cathode and anode.
- Operates with cadmium as an anode and nickel oxide hydroxide as a cathode in alkaline electrolyte.
- Common applications include portable electronics, emergency lighting, and cordless power tools.
Corrosion Overview
- Corrosion refers to the deterioration of metallic materials due to chemical or electrochemical reactions with the environment.
- Common examples include rusting of iron and the formation of green patina on copper.
- The rate of corrosion varies with the type of metal and environmental conditions.
- Noble metals like gold and silver corrode negligibly, while reactive metals like sodium and calcium corrode extensively.
Causes of Corrosion
- Metals are found in combined states as ores, typically in positive oxidation states, which is their stable form.
- Upon extraction, metals transition to a neutral state, becoming unstable and prone to reacting with environmental factors.
Types of Corrosion
- Corrosion can be classified into two main types: dry (chemical) corrosion and wet (electrochemical) corrosion.
Dry Corrosion
- Involves direct chemical attack by dry gases or anhydrous liquids.
- The rate of dry corrosion is influenced by:
- Chemical Affinity: Higher affinity leads to increased corrosion.
- Temperature: Higher temperatures accelerate corrosion.
- Corrosion Products: Volatile and porous products increase corrosion rates.
Mechanisms of Dry Corrosion
-
Oxidation Corrosion: Occurs when metals react with oxygen.
- Stable Oxides: Form protective layers (e.g., aluminum, copper).
- Porous Oxides: Allow continued corrosion if cracks are present.
- Unstable Oxides: Decompose, preventing sustained oxidation (e.g., silver).
- Volatile Oxides: Facilitate rapid corrosion by volatilizing and exposing fresh metal (e.g., MoO3).
-
Corrosion by Other Gases: Direct attack by gases like Cl2 or H2S accelerates corrosion depending on gas-metal affinity.
-
Hydrogen Corrosion: Atomic hydrogen can diffuse into metals, causing embrittlement and potential intergranular cracking.
-
Corrosion by Anhydrous Liquids: Attack by organic and inorganic liquids that can dissolve or penetrate metal surfaces, depending on temperature gradients.
Wet Corrosion
- Involves contact with electrolytes, creating anodic and cathodic areas for current flow.
- Anodic areas experience oxidation, while cathodic areas undergo reduction.
Types of Wet Corrosion Mechanisms
- Galvanic Corrosion: Occurs between dissimilar metals in an electrolyte, with the less noble metal corroding.
- Concentration Cell Corrosion: Differences in the concentration of ions can generate localized corrosion.
Specific Types of Corrosion
- Pitting Corrosion: Localized corrosion forming small pits, accelerated by aeration differences.
- Waterline Corrosion: Occurs in stagnant water, with oxygen-rich areas acting as cathodes.
- Intergranular Corrosion: Targets grain boundaries, influenced by impurities and environmental factors.
- Stress Corrosion: Results from tensile stress in conjunction with specific corrosive agents, leading to localized corrosion.
Corrosion Control Methods
-
Material Selection:
- Use metals with high corrosion resistance and purity.
- Alloying improves resistance.
-
Design Considerations:
- Ensure uniform stability in design.
- Avoid contact between dissimilar metals.
-
Cathodic Protection: Employ sacrificial anodes or impressed current to reduce the metal potential.
-
Protective Surface Coatings: Utilize paint or other coatings to shield metal from environmental exposure.
Key Principles
- Pilling Bedworth Rule: Protective oxides should have a volume greater than the metal volume to prevent continued corrosion. Porous oxides permit corrosion progression.
- Understanding these principles and corrosion mechanisms is essential for effective corrosion management in various applications.### Corrosion Prevention of Dissimilar Metals
- Anodic material should have a larger surface area compared to the cathodic metal to reduce corrosion rates.
- Coatings with insulating materials are critical to prevent direct contact between dissimilar metals.
- Anodic metal should not be fully coated to avoid rapid pitting if any breaks occur in the protective layer.
- Effective equipment design should minimize accumulation of corrosive materials and avoid sharp bends or localized stresses.
- Tanks and pipelines must be designed to eliminate obstructions and crevices.
Cathodic Protection Methods
- Cathodic protection forces a metal structure to act as a cathode using opposite external current to prevent corrosion.
- Sacrificial Anode Method: Involves connecting the metallic structure to a more active metal, which corrodes instead of the protected metal.
- Common sacrificial anodes include zinc, magnesium, and aluminum.
- Needs periodic replacement once the sacrificial anode is consumed.
- Impressed Current Method: Applies a current to counteract corrosion current, converting the corroding metal to a cathode.
- Utilizes a direct current source, such as a battery or rectifier.
- Anodes are often buried in conductive backfill to enhance soil contact.
- Suitable for large structures and offers reduced maintenance and operating costs.
Protective Surface Coatings
- Galvanizing: Coats iron or steel with zinc to prevent rusting.
- Involves cleaning steel with dilute sulfuric acid followed by dipping in molten zinc at 425-430°C.
- A flux of ammonium chloride prevents oxide formation during the process.
- Commonly used for roofing sheets, pipes, and containers.
- Tinning: Coats steel, copper, or brass with tin.
- Steel is first treated with diluted sulfuric acid, then passes through zinc chloride flux, followed by molten tin.
- The tin-coated surface is protected by palm oil during processing.
Battery Technology
- Batteries convert chemical energy to electrical energy through redox reactions involving oxidation and reduction.
- A battery comprises multiple electrochemical cells which consist of anodes, cathodes, and electrolytes.
- Terminal voltage is measured across battery terminals; open circuit voltage is the EMF when not under load.
Types of Batteries
- Primary Batteries: Non-rechargeable; electrode reactions are irreversible.
- Secondary Batteries: Rechargeable, allowing reversible electrode reactions.
Nickel-Cadmium (Ni-Cd) Battery
- First sealed rechargeable battery, exhibiting long cycle life and good performance even at low temperatures.
- Construction features a jelly-roll design with a sealed metal case, including separators for cathode and anode.
- Operates with cadmium as an anode and nickel oxide hydroxide as a cathode in alkaline electrolyte.
- Common applications include portable electronics, emergency lighting, and cordless power tools.
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Description
This quiz covers Unit II of the course on Corrosion and Energy Storage Systems. It focuses on the chemical processes involved in corrosion, including examples such as rusting of iron and copper corrosion. Understand the factors that influence corrosion in various metallic materials.
