Corrosion and Protection Quiz
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Questions and Answers

What is the primary cause of corrosion in metals?

  • Direct contact with water only
  • Stability of metals in their pure state
  • Heat exposure
  • Deterioration due to environmental elements (correct)

Which type of corrosion involves the direct attack of atmospheric gases?

  • Dry or chemical corrosion (correct)
  • Differential aeration corrosion
  • Galvanic corrosion
  • Wet or electrochemical corrosion

Which of the following is NOT a method of corrosion protection?

  • Organic coatings
  • Galvanization
  • Increased temperature exposure (correct)
  • Tinning

What is the Pilling Bedworth ratio used for in the context of corrosion?

<p>Assessing the stability of metal oxides (D)</p> Signup and view all the answers

Which type of corrosion occurs due to differences in oxygen concentration?

<p>Differential aeration corrosion (D)</p> Signup and view all the answers

Which factor does NOT affect the rate of corrosion?

<p>Color of the metal (C)</p> Signup and view all the answers

Inhibitors used for corrosion prevention can be categorized as?

<p>Cathodic and anodic (D)</p> Signup and view all the answers

Which painting constituent functions primarily to prevent the penetration of moisture?

<p>Binders (C)</p> Signup and view all the answers

What is oxidation corrosion primarily caused by?

<p>Direct action of oxygen on the metal surface (B)</p> Signup and view all the answers

What phenomenon describes the process where oxygen atoms adhere to the metal surface?

<p>Chemisorption (A)</p> Signup and view all the answers

What is the primary role of a vehicle in paint?

<p>To provide adhesion, cohesion, and flexibility (A)</p> Signup and view all the answers

Which metal has the least rate of oxidation based on specific volume ratios?

<p>Tungsten (B)</p> Signup and view all the answers

Which type of oxide layer is most effective in preventing further oxidation of the metal?

<p>Stable oxide (D)</p> Signup and view all the answers

Which of the following is NOT considered a common thinner for paint?

<p>Linseed oil (C)</p> Signup and view all the answers

What is the primary characteristic of the oxide formed by aluminum?

<p>Non-porous and protective (B)</p> Signup and view all the answers

According to the Pilling Bedworth Rule, when is an oxide layer considered protective?

<p>If its volume is greater than or equal to the metal's volume (A)</p> Signup and view all the answers

What is the function of driers in paint formulations?

<p>To improve the drying quality of the oil film (D)</p> Signup and view all the answers

In wet corrosion, what occurs at the anodic area?

<p>Dissolution of metal (B)</p> Signup and view all the answers

What happens if a volatile oxide product is formed during oxidation corrosion?

<p>It allows fresh metal surface exposure, increasing corrosion (C)</p> Signup and view all the answers

What is the primary benefit of using extenders or fillers in paint?

<p>To reduce costs and improve durability (B)</p> Signup and view all the answers

What type of oxide layer is characterized by allowing uninterrupted oxidation reactions?

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

What type of corrosion involves the chemical action of a flowing liquid metal?

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

Which of the following serves as an anti skinning agent in paint?

<p>Methylated naphthalene (B)</p> Signup and view all the answers

Which gas is known to form a protective film on metals?

<p>Sulfur dioxide (A)</p> Signup and view all the answers

Which of the following statements is true about oxidation in metals?

<p>Oxidation is the loss of electrons from the metal. (C)</p> Signup and view all the answers

Which type of oil is classified as a commonly used drying oil?

<p>Dehydrated castor oil (C)</p> Signup and view all the answers

What condition increases oxidation corrosion concerning the specific volume ratio?

<p>Smaller ratio of oxide volume to metal volume (B)</p> Signup and view all the answers

What happens to the dissolved constituents at the cathodic area during corrosion?

<p>They gain electrons (A)</p> Signup and view all the answers

Which material is primarily used as a filler in paint to reduce cracking?

<p>Barytes (BaSO4) (C)</p> Signup and view all the answers

What is the main purpose of plasticizers in paint formulations?

<p>To provide elasticity and minimize cracking (A)</p> Signup and view all the answers

Which of the following reactions primarily occurs in wet corrosion?

<p>Flow of electric current between areas (A)</p> Signup and view all the answers

What role does H2S play in corrosion processes?

<p>Forms a porous FeS film (B)</p> Signup and view all the answers

What is the primary purpose of a cathodic coating?

<p>To provide effective protection to the base metal (A)</p> Signup and view all the answers

Which metallic coating process is used to coat iron or steel with zinc?

<p>Galvanizing (B)</p> Signup and view all the answers

What is the role of the flux in the hot dipping process?

<p>To clean the base metal surface (B)</p> Signup and view all the answers

Why should galvanized utensils not be used for storing food?

<p>They may dissolve zinc, forming toxic substances. (D)</p> Signup and view all the answers

What method is commonly used to clean base metal surfaces before coating?

<p>Acid pickling (B)</p> Signup and view all the answers

What is the characteristic of the coating process referred to as 'tinning'?

<p>It applies a layer of metallic tin. (C)</p> Signup and view all the answers

What are the two most commonly applied hot dipping methods?

<p>Tinning and galvanizing (D)</p> Signup and view all the answers

Which process involves immersion of the base metal in a bath of molten coating metal?

<p>Hot dipping (B)</p> Signup and view all the answers

What effect does the relative area of cathodic and anodic parts have on corrosion rates?

<p>Corrosion increases as the anodic area decreases. (C)</p> Signup and view all the answers

How does the purity of a metal influence corrosion resistance?

<p>Increased purity generally enhances corrosion resistance. (C)</p> Signup and view all the answers

What happens to the rate of corrosion when the temperature of the environment increases?

<p>Corrosion rate generally increases with temperature. (D)</p> Signup and view all the answers

What is defined as 'critical humidity' in relation to atmospheric corrosion?

<p>The humidity above which corrosion rates increase sharply. (D)</p> Signup and view all the answers

Which of the following factors contributes to increased atmospheric corrosion in industrial areas?

<p>Increased acidity due to corrosive gases and moisture. (A)</p> Signup and view all the answers

How does the physical state of a metal affect its corrosion rate?

<p>Smaller grain size results in higher solubility and corrosion rates. (D)</p> Signup and view all the answers

In what kind of media are amphoteric metals like Al and Pb more likely to dissolve?

<p>Acidic media, forming complex ions. (B)</p> Signup and view all the answers

What role do environmental impurities play in corrosion?

<p>They can enhance the conductivity and acidity of the adjacent liquid. (A)</p> Signup and view all the answers

Flashcards

Corrosion

The deterioration and destruction of materials caused by unwanted chemical reactions with the environment, leading to loss of material from the surface.

Dry Corrosion

Corrosion that occurs through a direct chemical reaction between a metal and gases in the atmosphere.

Wet Corrosion

Corrosion that occurs when a metal is in contact with an electrolyte, like water, and there are different electrical potentials between parts of the metal surface.

Galvanic Series

The tendency of a metal to corrode, based on its position in the Galvanic Series.

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Differential Aeration Corrosion

Corrosion caused by differences in oxygen concentration on a metal surface.

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Galvanic Corrosion

Corrosion that occurs when two dissimilar metals are in electrical contact in an electrolyte.

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Pitting Corrosion

Corrosion that occurs in localized areas, creating small pits or holes in the metal.

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Galvanization

A type of corrosion protection method where a more reactive metal, like zinc, is applied to a less reactive metal, like steel.

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Oxidation Corrosion

A type of corrosion where oxygen directly interacts with the metal surface in the absence of moisture. This reaction leads to the formation of a metal oxide.

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Chemisorption

The phenomenon where oxygen atoms weakly attach to the metal surface through Vander Waal forces. This attachment eventually results in the formation of bonds, transforming the metal into its oxide.

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Stable Oxide Layer

A protective oxide film that forms on the metal surface due to oxidation. It acts as a barrier, preventing further corrosion.

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Unstable Oxide Layer

An unstable oxide film that quickly decomposes, allowing further corrosion to occur.

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Volatile Oxide Layer

An oxide film that evaporates, leaving a fresh metal surface vulnerable to further corrosion.

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Porous Oxide Layer

An oxide film with pores that allow the corrosion reaction to continue unimpeded. This leads to rapid and extensive corrosion.

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Pilling-Bedworth Rule

A rule stating that a metal oxide layer is protective if its volume is equal to or greater than the volume of the metal it was formed from. If the oxide volume is smaller, the layer is porous and non-protective.

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Specific Volume Ratio

The ratio of the oxide's volume to the original metal's volume. A smaller ratio indicates a more porous, non-protective oxide layer, making the metal more prone to oxidation corrosion.

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Gaseous Corrosion

The process of metal deterioration caused by chemical reaction between metal and gas.

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Liquid Metal Corrosion

Corrosion caused by the chemical reaction of a liquid metal with a solid metal.

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Anodic Area

The area on a metal surface where oxidation takes place during corrosion.

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Cathodic Area

The area on a metal surface where reduction takes place during corrosion.

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Protective/Non-Protective Films

A thin layer that forms on a metal surface during corrosion, which can either protect the metal or accelerate corrosion.

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Corrosion Rate

The speed at which a metal corrodes.

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Area Ratio and Corrosion

The corrosion rate of a metal is directly proportional to the ratio of cathodic area to anodic area. A smaller anodic area experiences higher current density, leading to faster and more localized corrosion.

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Impurities and Corrosion

Impurities in a metal create heterogeneity, leading to the formation of electrochemical cells where the anodic part corrodes. The rate of corrosion increases with the impurity concentration.

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Grain Size and Corrosion

Metals with smaller grain sizes generally have higher solubility, which contributes to faster corrosion rates.

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Temperature and Corrosion

Higher temperatures generally increase reaction rates and diffusion, accelerating corrosion.

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Humidity and Corrosion

Humidity is a crucial factor in atmospheric corrosion. Corrosion rates increase significantly above a certain humidity level known as 'critical humidity'.

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Atmospheric Impurities and Corrosion

Corrosive gases in the atmosphere can increase acidity and conductivity, leading to faster corrosion.

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pH and Corrosion

Acidic environments generally cause faster corrosion compared to alkaline or neutral media.

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Amphoteric Metals and Corrosion

Certain metals like aluminum and lead can dissolve in alkaline solutions as complex ions, which can contribute to their corrosion.

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Cathodic Coating

A protective layer that prevents corrosion by acting as a barrier between the metal and the environment. It works by being more easily oxidized than the base metal.

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Hot Dipping

A method of applying a thin coating of a low-melting metal like zinc, tin, or lead to a higher-melting base metal like iron or steel. The process involves immersing the base metal in a bath of molten coating metal.

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Galvanizing

A type of hot dipping used to coat iron or steel sheets with a layer of zinc, preventing rust. It involves cleaning the metal, dipping it in molten zinc, removing excess zinc by rollers, and annealing.

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Why can't galvanized utensils be used for storing food?

Galvanized utensils should not be used for storing food.

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Tinning

A common process used to coat iron and steel articles with a thin layer of tin. It helps prevent corrosion and improve the surface properties of the metal. It involves cleaning the base metal with acid, passing it through a flux, and then dipping it in molten tin.

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Flux (in hot dipping)

A substance used in hot dipping to clean and prepare the surface of the base metal before coating. It also prevents oxidation of the molten coating metal.

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Why is cleaning the base metal essential in hot dipping?

The surface of the base metal must be thoroughly cleaned before hot dipping to ensure good adhesion of the coating metal.

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Annealing

The process of slowly cooling a metal after heating it to a high temperature. It helps to improve the metal's properties, such as its strength and ductility.

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Vehicle (or) drying oil

A component of paint that forms a film, providing desired properties like adhesion, cohesion, and flexibility.

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Linseed oil

A type of drying oil used in paints, known for its ability to dry quickly and form a strong film.

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Thinner

Substances in paint that reduce its viscosity, making it easier to apply and allowing pigments to disperse.

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Driers

Chemicals that accelerate the drying process of oil-based paints by promoting oxidation, polymerization, and condensation.

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Extenders or fillers

Materials added to paint to lower its cost, increase durability, and improve the film's appearance, by filling in gaps and providing a uniform texture.

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Plasticizers

Substances that enhance the flexibility of paint films, preventing cracking and improving their ability to stretch.

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Anti-skinning agents

Chemicals added to prevent the formation of a solid skin on the surface of paint, ensuring that it remains usable for longer.

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Turpentine

A type of paint thinner that is a common solvent used in painting and varnishing.

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Study Notes

Corrosion

  • Corrosion is the deterioration or destruction of a material due to unwanted environmental attack, causing loss of matter from its surface.
  • Examples include rusting of iron, silver tarnishing, and the formation of copper carbonate.
  • Metals are more stable in their mineral/compound state than in their pure form (except gold).
  • Corrosion is a significant engineering challenge due to substantial material loss.

Theories of Corrosion

  • Corrosion is broadly classified into dry (chemical) and wet (electrochemical) types.

Dry (Chemical) Corrosion

  • Dry corrosion results from direct gaseous attacks (e.g., O2, CO2, H2S, SO2, halogens) on metal surfaces.
  • Three types of dry corrosion are:
    • Oxidation corrosion: Direct oxygen attack, forming metal oxides.
    • Corrosion by other gases: Attack by gases like CO2, H2S, SO2.
    • Liquid metal corrosion: Corrosion by flowing liquid metals.

Wet (Electrochemical) Corrosion

  • Wet corrosion occurs when dissimilar metals or alloys are immersed or dipped in a conducting liquid.
  • Two distinct areas form (anode and cathode) with different potentials, where oxidation (anode) and reduction (cathode) occur, respectively.
  • Wet corrosion involves electron flow between anodic and cathodic regions.

Pilling-Bedworth Rule

  • Protective oxides form a layer over the affected surface of metal, acting to limit the corrosion process.
  • The layer will be protective if the volume of the oxide formed is at least equal to or larger than that of the original metal
  • Otherwise, a porous oxide layer forms, increasing the corrosion rate.

Types of Corrosion

  • Galvanic Corrosion: Corrosion occurs when dissimilar metals/alloys connect electrically in a corrosive environment. The more reactive metal (higher in the galvanic series) serves as the anode with greater corrosion.
  • Concentration Cell Corrosion: Corrosion occurs in areas of different oxygen concentration or varying electrolyte concentrations. Lower oxygen concentration or lower concentration regions become anodic.
  • Waterline Corrosion: Corrosion occurs at the waterline of submerged metal surfaces due to variable oxygen concentration (water surface is highly oxygenated while submerged parts have less oxygen).
  • Pitting Corrosion: Localized, intense corrosion that occurs in concentrated spots on a metal's surface. Breakdown of protective surface films causes the attack.
  • Stress Corrosion: Corrosion results from a combination of tensile stress and a corrosive environment. Corrosion occurs specifically at locations where high mechanical stresses are present.

Corrosion Prevention

  • Metallic Coatings: Applying a layer of a different, more corrosion-resistant metal (e.g., galvanizing, tinning) to the surface of the material.
    • Anodic coatings (sacrificial): Protected metal is rendered cathodic, thus preventing corrosion (e.g., zinc coating on steel).
    • Cathodic coatings: Higher corrosion-resistant coating (e.g., chromium plating).
  • Inhibitors: Adding substances to the corrosive environment that slow down the rate of corrosion.
  • Cathodic Protection: Applying an external current to the metal surface to control the electron flow (e.g., impressed current, sacrificial anode).
  • Design Considerations: Using proper design to prevent stagnant areas, crevices, and dissimilar metal contacts.
  • Use of Pure Metals: Using pure metals minimizes the presence of impurities that can cause corrosion.

Constituents of Paints

  • Pigment: Provides color and increases the strength/durability of the paint film.
  • Vehicle: Liquid binder that binds pigments and other additives to provide coating properties.
  • Thinner: Liquid solvent used to reduce viscosity, helping the paint flow easily and dry uniformly.
  • Driers: Catalysts that accelerate the drying process of the paint film.
  • Extenders/Fillers: Increase durability and reduces cost while providing coating characteristics.
  • Plasticizers: Additives improving paint flexibility.
  • Anti-skinning Agents: Prevents gelling and skinning in the paint.

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Corrosion 2019-20 PDF

Description

Test your knowledge on the various types of corrosion, their causes, and methods of protection. This quiz covers key concepts related to metal oxidation and prevention strategies. Perfect for students studying materials science or engineering.

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