Corrosion and Energy Storage Systems - Unit II
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Questions and Answers

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?

  • 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?

  • 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?

    <p>They exist in a combined state with ores.</p> Signup and view all the answers

    Which type of corrosion results from a direct chemical attack from dry gases or anhydrous liquids?

    <p>Dry corrosion</p> Signup and view all the answers

    What effect does increasing temperature have on the rate of corrosion?

    <p>It increases the extent of corrosion.</p> Signup and view all the answers

    What type of corrosion involves reactions between metals and moisture?

    <p>Wet corrosion</p> Signup and view all the answers

    What characteristic of stable oxides prevents the corrosion of heavy metals?

    <p>They form a protective coating that limits exposure to oxygen.</p> Signup and view all the answers

    Which type of oxide layer is likely to result in continued corrosion until the metal is completely oxidized?

    <p>Porous oxide</p> Signup and view all the answers

    Which phenomenon occurs when atomic hydrogen diffuses into a metal and affects its strength?

    <p>Hydrogen embrittlement</p> Signup and view all the answers

    What type of corrosion occurs when anhydrous liquids attack metal surfaces?

    <p>Liquid metal corrosion</p> Signup and view all the answers

    During electrochemical corrosion, what happens at the anodic area?

    <p>Metal ions are formed through oxidation.</p> Signup and view all the answers

    Which factor influences the rate of corrosion by dry gases?

    <p>Affinity between metal and reacting gases</p> Signup and view all the answers

    What type of oxide is characterized by its ability to rapidly evaporate once formed?

    <p>Volatile oxide</p> Signup and view all the answers

    In which reaction does oxidation occur at the anode, while reduction takes place at the cathode?

    <p>Electrochemical corrosion</p> Signup and view all the answers

    What happens to metals when they form unstable oxides?

    <p>They temporarily oxidize and decompose back into metal and oxygen.</p> Signup and view all the answers

    What is the primary purpose of using a sacrificial anode in cathodic protection?

    <p>To concentrate corrosion on a more active metal instead of the protected structure</p> Signup and view all the answers

    Which of the following processes is involved in galvanizing iron or steel?

    <p>Cleaning with dilute H2SO4 and dipping in molten zinc</p> Signup and view all the answers

    What is the main difference between primary batteries and secondary batteries?

    <p>Primary batteries have irreversible reactions while secondary batteries have reversible reactions</p> Signup and view all the answers

    What should be avoided in the design of equipment to prevent localized corrosion?

    <p>Creating smooth surfaces without sharp bends</p> Signup and view all the answers

    In the impressed current method of cathodic protection, what is typically used as the rectifying element?

    <p>A direct current source like a battery or rectifier</p> Signup and view all the answers

    What occurs at the anode during the Hydrogen Evolution Mechanism of corrosion?

    <p>Fe atoms undergo oxidation to form Fe2+ ions.</p> Signup and view all the answers

    In which type of corrosion does H2 gas evolve at the cathode?

    <p>Hydrogen Evolution Mechanism</p> Signup and view all the answers

    What occurs at the anode during galvanic corrosion?

    <p>Oxidation of zinc</p> Signup and view all the answers

    What is the primary product formed when ferrous hydroxide is oxidized in the presence of enough oxygen?

    <p>Fe(OH)3</p> Signup and view all the answers

    Which type of corrosion results from a difference in aeration levels in a stagnant water environment?

    <p>Waterline corrosion</p> Signup and view all the answers

    Which condition is necessary for stress corrosion to occur?

    <p>Static tensile stress</p> Signup and view all the answers

    Under which condition does inter-granular corrosion primarily occur?

    <p>Due to impurities precipitating at grain boundaries</p> Signup and view all the answers

    What is a primary factor affecting corrosion resistance in metals?

    <p>Purity of the metals</p> Signup and view all the answers

    Which process intensifies corrosion for metals like mild steel in alkaline solutions?

    <p>Caustic embrittlement</p> Signup and view all the answers

    Which reaction occurs at the cathode during the Oxygen Absorption Mechanism?

    <p>1/2O2 + e- + H2O → 2OH-</p> Signup and view all the answers

    What is a common control method for preventing pitting corrosion?

    <p>Applying antifouling paints</p> Signup and view all the answers

    According to the Pilling Bedworth rule, what determines if an oxide layer is protective?

    <p>Volume compared to the metal it is formed from</p> Signup and view all the answers

    What leads to the formation of pits in metals during pitting corrosion?

    <p>Deep penetration of air bubbles during cooling</p> Signup and view all the answers

    What alloying component in copper can lead to season cracking in the presence of ammonia?

    <p>Zinc</p> Signup and view all the answers

    Why does oxygen absorption corrosion typically have a small anodic area?

    <p>Dissolved oxygen is only present in limited amounts.</p> Signup and view all the answers

    What role does cathodic protection play in corrosion control?

    <p>It sacrifices a more reactive metal to protect another.</p> Signup and view all the answers

    What happens to Fe2+ ions and hydroxide ions during the oxidation reaction in the Oxygen Absorption Mechanism?

    <p>They combine to form ferrous hydroxide precipitate.</p> Signup and view all the answers

    What happens to the corrosion rate when a metal's internal stress is reduced through proper heat treatment?

    <p>It can decrease.</p> Signup and view all the answers

    Which combination fosters corrosion when using dissimilar metals in construction?

    <p>Large area of anodic material and small area of cathodic material</p> Signup and view all the answers

    Which environment can cause stress corrosion specifically in mild steel?

    <p>Caustic alkali solutions</p> Signup and view all the answers

    What is the main reason metals corrode when extracted from their ores?

    <p>They become unstable in their neutral state.</p> Signup and view all the answers

    Which factor is NOT mentioned as influencing dry corrosion?

    <p>Humidity levels</p> Signup and view all the answers

    Which type of corrosion involves a direct chemical attack from gases or anhydrous liquids?

    <p>Dry corrosion</p> Signup and view all the answers

    What effect does the formation of volatile corrosion products have on the rate of corrosion?

    <p>Increases the rate of corrosion</p> Signup and view all the answers

    What happens to metals with high chemical affinity towards their environmental factors?

    <p>They corrode at an accelerated rate.</p> Signup and view all the answers

    In the context of corrosion, what is the definition of wet corrosion?

    <p>Corrosion due to moisture presence.</p> Signup and view all the answers

    Which metals are known to corrode to a considerable extent?

    <p>Heavy metals like tungsten and chromium</p> Signup and view all the answers

    What is the purpose of not completely coating anodic metals with protective coatings?

    <p>To prevent rapid pitting corrosion if a breach occurs.</p> Signup and view all the answers

    Which method of cathodic protection uses a more active metal to protect a metallic structure?

    <p>Sacrificial anode method.</p> Signup and view all the answers

    What are the two methods of cathodic protection outlined in the information?

    <p>Sacrificial Anode and Impressed Current.</p> Signup and view all the answers

    What chemical process is primarily involved in battery operation?

    <p>Redox reactions.</p> Signup and view all the answers

    Which type of battery consists of irreversible electrode reactions?

    <p>Primary batteries.</p> Signup and view all the answers

    What occurs at the anode during galvanic corrosion?

    <p>Oxidation of the metal</p> Signup and view all the answers

    What is the primary cause of stress corrosion?

    <p>Combining tensile stress with specific corrosive environments</p> Signup and view all the answers

    What gas is evolved at the cathode during the Hydrogen Evolution Mechanism of corrosion?

    <p>Hydrogen</p> Signup and view all the answers

    Which type of oxide layer is most effective at preventing further corrosion?

    <p>Non-porous oxide layer</p> Signup and view all the answers

    What is a common method to improve a metal's corrosion resistance?

    <p>Proper heat treatment</p> Signup and view all the answers

    What type of corrosion occurs when oxygen gas is absorbed at the cathode?

    <p>Oxygen Absorption Corrosion</p> Signup and view all the answers

    Which type of corrosion primarily involves localized attack in the form of pits?

    <p>Pitting Corrosion</p> Signup and view all the answers

    What happens to the metal at the cathodic area during galvanic corrosion?

    <p>It remains unaffected and protected</p> Signup and view all the answers

    What is season cracking primarily associated with?

    <p>Copper alloys in the presence of ammonia</p> Signup and view all the answers

    In waterline corrosion, which part of the metal acts as the anode?

    <p>Below the water line</p> Signup and view all the answers

    What reaction occurs at the anode during the oxidation process in electrochemical corrosion?

    <p>Fe → Fe2+ + 2e-</p> Signup and view all the answers

    Which factor primarily influences the state of corrosion resistance in alloyed metals?

    <p>The purity and alloying components used</p> Signup and view all the answers

    What primarily causes inter-granular corrosion?

    <p>Presence of impurities at grain boundaries</p> Signup and view all the answers

    According to the Pilling Bedworth rule, what characterizes a protective oxide layer?

    <p>It has a volume equal to or greater than that of the metal</p> Signup and view all the answers

    Which control method can help prevent pitting corrosion?

    <p>Employing sacrificial anodes</p> Signup and view all the answers

    Which combination of conditions is most likely to foster stress corrosion in metals?

    <p>Static tension and specific corrosive agents</p> Signup and view all the answers

    What is the end product when enough oxygen is present during the oxidation of ferrous hydroxide?

    <p>Ferric Hydroxide</p> Signup and view all the answers

    What is cathodic protection primarily used for?

    <p>Preventing oxidation of metals</p> Signup and view all the answers

    How can waterline corrosion be controlled?

    <p>Using antifouling paints</p> Signup and view all the answers

    Which mechanism primarily leads to hydrogen gas evolution at the cathode?

    <p>Hydrogen Evolution Mechanism</p> Signup and view all the answers

    What characteristic of stable oxides helps protect heavy metals from corrosion?

    <p>They form a protective layer that prevents oxygen contact.</p> Signup and view all the answers

    What type of oxide layer is likely to cause continued corrosion due to its porous structure?

    <p>Porous oxide</p> Signup and view all the answers

    What occurs during the process of hydrogen embrittlement?

    <p>Atomic hydrogen diffuses into the metal causing losses in ductility.</p> Signup and view all the answers

    Which type of corrosion is characterized by the presence of anodic and cathodic areas in the presence of an electrolyte?

    <p>Electrochemical corrosion</p> Signup and view all the answers

    What is a common characteristic of volatile oxides?

    <p>They easily vaporize after formation, exposing fresh metal.</p> Signup and view all the answers

    What is a potential consequence of corrosion by anhydrous liquids?

    <p>Complete dissolution of the metal surface.</p> Signup and view all the answers

    In wet or electrochemical corrosion, what occurs at the cathodic area?

    <p>Reduction reactions occur.</p> Signup and view all the answers

    Which type of oxide forms an unstable layer that can decompose back into the metal?

    <p>Unstable oxide</p> Signup and view all the answers

    What was a consequence observed when chlorination attacks tin?

    <p>Creation of volatile stannic chloride.</p> Signup and view all the answers

    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.

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