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?

Assessing the stability of metal oxides Signup and view all the answers

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

Differential aeration corrosion Signup and view all the answers

Which factor does NOT affect the rate of corrosion?

Color of the metal Signup and view all the answers

Inhibitors used for corrosion prevention can be categorized as?

Cathodic and anodic Signup and view all the answers

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

Binders Signup and view all the answers

What is oxidation corrosion primarily caused by?

Direct action of oxygen on the metal surface Signup and view all the answers

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

Chemisorption Signup and view all the answers

What is the primary role of a vehicle in paint?

To provide adhesion, cohesion, and flexibility Signup and view all the answers

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

Tungsten Signup and view all the answers

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

Stable oxide Signup and view all the answers

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

Linseed oil Signup and view all the answers

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

Non-porous and protective Signup and view all the answers

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

If its volume is greater than or equal to the metal's volume Signup and view all the answers

What is the function of driers in paint formulations?

To improve the drying quality of the oil film Signup and view all the answers

In wet corrosion, what occurs at the anodic area?

Dissolution of metal Signup and view all the answers

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

It allows fresh metal surface exposure, increasing corrosion Signup and view all the answers

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

To reduce costs and improve durability Signup and view all the answers

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

Porous oxide Signup and view all the answers

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

Liquid metal corrosion Signup and view all the answers

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

Methylated naphthalene Signup and view all the answers

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

Sulfur dioxide Signup and view all the answers

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

Oxidation is the loss of electrons from the metal. Signup and view all the answers

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

Dehydrated castor oil Signup and view all the answers

What condition increases oxidation corrosion concerning the specific volume ratio?

Smaller ratio of oxide volume to metal volume Signup and view all the answers

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

They gain electrons Signup and view all the answers

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

Barytes (BaSO4) Signup and view all the answers

What is the main purpose of plasticizers in paint formulations?

To provide elasticity and minimize cracking Signup and view all the answers

Which of the following reactions primarily occurs in wet corrosion?

Flow of electric current between areas Signup and view all the answers

What role does H2S play in corrosion processes?

Forms a porous FeS film Signup and view all the answers

What is the primary purpose of a cathodic coating?

To provide effective protection to the base metal Signup and view all the answers

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

Galvanizing Signup and view all the answers

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

To clean the base metal surface Signup and view all the answers

Why should galvanized utensils not be used for storing food?

They may dissolve zinc, forming toxic substances. Signup and view all the answers

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

Acid pickling Signup and view all the answers

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

It applies a layer of metallic tin. Signup and view all the answers

What are the two most commonly applied hot dipping methods?

Tinning and galvanizing Signup and view all the answers

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

Hot dipping Signup and view all the answers

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

Corrosion increases as the anodic area decreases. Signup and view all the answers

How does the purity of a metal influence corrosion resistance?

Increased purity generally enhances corrosion resistance. Signup and view all the answers

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

Corrosion rate generally increases with temperature. Signup and view all the answers

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

The humidity above which corrosion rates increase sharply. Signup and view all the answers

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

Increased acidity due to corrosive gases and moisture. Signup and view all the answers

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

Smaller grain size results in higher solubility and corrosion rates. Signup and view all the answers

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

Acidic media, forming complex ions. Signup and view all the answers

What role do environmental impurities play in corrosion?

They can enhance the conductivity and acidity of the adjacent liquid. Signup and view all the answers

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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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.