Understanding Corrosion and Its Effects

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Questions and Answers

What is a primary characteristic of dry or chemical corrosion?

Occurs primarily in the presence of moisture

Only affects metallic surfaces in liquids

Is solely caused by temperature fluctuations

Involves the direct attack of atmospheric gases (correct)

Which type of corrosion results from the direct action of oxygen on a metal surface without moisture?

Corrosion by halogens

Wet corrosion

Oxidation corrosion (correct)

Liquid metal corrosion

What is a significant financial impact attributed to corrosion worldwide?

$5 billion per annum

$2 to $2.5 billion per annum (correct)

$1 billion per annum

$10 billion per annum

What phenomenon converts metal into its corresponding metal oxide during oxidation corrosion?

Chemisorption Signup and view all the answers

Which of the following factors is NOT primarily associated with the losses incurred due to corrosion?

Increased fluid viscosity Signup and view all the answers

What is the primary cause of corrosion?

Unwanted interaction with the environment Signup and view all the answers

Which of the following is an example of corrosion?

Rust formation on iron Signup and view all the answers

What can be a direct consequence of localized corrosion?

Development of cracklike structures Signup and view all the answers

Which type of engineering specifically addresses the issue of corrosion?

Corrosion engineering Signup and view all the answers

Which of the following does NOT describe a consequence of corrosion?

Increase in structural integrity Signup and view all the answers

What is a visible sign of copper corrosion when exposed to damp air containing CO2?

A green film of basic carbonate Signup and view all the answers

What is a potential hazard caused by the consequences of corrosion?

Hazards to human safety Signup and view all the answers

How does corrosion impact the value of goods?

Leads to deterioration of appearance Signup and view all the answers

What characterizes the areas of anodic and cathodic regions in the oxide film?

Anodic areas are small and cathodic areas are large. Signup and view all the answers

What is formed at the anode during corrosion of iron?

Fe2+ ions and electrons Signup and view all the answers

What is the end product of the reaction between Fe2+ ions and OH- ions?

Fe(OH)2 Signup and view all the answers

Under what condition does electrochemical corrosion primarily occur?

In the presence of electrolytes Signup and view all the answers

What happens to ferrous hydroxide (Fe(OH)2) if sufficient oxygen is available?

It transforms into hydrated ferric oxide. Signup and view all the answers

Which type of corrosion requires moisture to be present?

Electrochemical Corrosion Signup and view all the answers

What is the main difference between chemical and electrochemical corrosion?

Chemical corrosion occurs in dry conditions; electrochemical occurs in wet conditions. Signup and view all the answers

What is the final product when ferrous hydroxide is fully oxidized?

Fe2O3·xH2O (rust) Signup and view all the answers

What is the primary driving force behind galvanic corrosion?

Electrode potential Signup and view all the answers

Which combination of conditions is necessary for galvanic corrosion to occur?

Two dissimilar metals, electrical contact, and a conductive electrolyte Signup and view all the answers

When zinc and copper are connected, which metal acts as the anode in galvanic corrosion?

Zinc Signup and view all the answers

What happens if there is a plastic washer between two metals in a galvanic corrosion scenario?

Galvanic corrosion cannot occur Signup and view all the answers

In a galvanic series, the term 'electrode potential' refers to which of the following?

The likelihood of a metal to corrode Signup and view all the answers

Which of the following is not a condition required for galvanic corrosion?

Non-conductive environment Signup and view all the answers

Which example best illustrates galvanic corrosion?

Zinc coating on mild steel immersed in salt water Signup and view all the answers

What effect does moisture have in the context of galvanic corrosion?

Facilitates a conductive path between metals Signup and view all the answers

What characterizes pitting corrosion?

Localized attack resulting in pits and cavities Signup and view all the answers

In the context of waterline corrosion, which area of the metal is most anodic?

Just below the waterline Signup and view all the answers

Which metals are more susceptible to corrosion due to their position in the galvanic series?

Li, Na, Mg, Zn Signup and view all the answers

What primarily causes differential aeration corrosion in submerged metals?

Oxygen concentration differences Signup and view all the answers

What happens to the protective film on a metal surface that leads to pitting corrosion?

It breaks down due to external factors Signup and view all the answers

Which type of environment increases the risk of pitting corrosion?

Presence of stagnant water with low oxygen Signup and view all the answers

What is the effect of increasing reduction potential on a metal's tendency to corrode?

It decreases the tendency to corrode Signup and view all the answers

Which of the following metals is considered a noble metal with high reduction potential?

Platinum Signup and view all the answers

Study Notes

Definition of Corrosion

Corrosion is the deterioration and destruction of materials caused by environmental reactions, usually starting at the surface.
It converts refined metals into stable forms such as oxides, hydroxides, or sulfides.
Corrosion engineering focuses on prevention and control strategies.

Examples of Corrosion

Rusting of iron results in the formation of reddish Fe3O4 powder.
Copper exposed to moist air with CO2 develops a green film of basic carbonate [CuCO3 + Cu(OH)2].

Consequences of Corrosion

Reduction in metal thickness can lead to structural failures.
Localized metal loss can create crack-like structures, severely weakening materials.
Structural failures pose hazards to public safety, affecting bridges, vehicles, and aircraft.
Time lost and increased costs in maintaining industrial equipment due to corrosion.
Aesthetic deterioration reduces the value of goods.
Corrosion can cause contamination of fluids, prompting safety and health concerns.
Pipe perforation can lead to environmental contamination and costly damages.
Loss of important surface properties affects functionality and performance of components.
Estimated global annual losses due to corrosion range between 2to2 to 2to2.5 billion.

Types of Corrosion

Dry or Chemical Corrosion

Occurs due to direct atmospheric gas attacks in the absence of moisture.
Involves gases like oxygen, halogens, and sulfur oxides.

Oxidation Corrosion

Direct interaction of oxygen with metal surfaces leads to metal oxide formation through chemisorption.

Electrochemical Corrosion

Takes place in wet conditions, involving electrolytes.

Galvanic or Bimetallic Corrosion

Occurs when dissimilar metals in contact undergo corrosion due to differences in their electrochemical series.
Example: Zinc acts as an anode when connected to copper, often used in pipelines, marine hardware, etc.

Requirements for Galvanic Corrosion

Presence of two metals with differing corrosion potentials.
Direct metal-to-metal electrical contact.
A conductive electrolyte must bridge the two metals to facilitate corrosion.

Pitting Corrosion

Characterized by local, intense attacks leading to pinholes and cavities.
Often results from protective film breakdown due to mechanical wear or environmental stress.

Waterline Corrosion

Significant corrosion occurs beneath the waterline due to differential aeration; areas above are well-oxygenated and act as cathodes while submerged areas become anodic.

Factors Influencing Corrosion

Metals with low reduction potentials are more reactive and susceptible to corrosion (e.g., Li, Na, Mg, Zn).
Noble metals, such as Ag, Au, and Pt, have high reduction potentials, making them less prone to corrosion.

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Description

This quiz explores the causes, examples, and consequences of corrosion, an important topic in materials engineering. Learn how corrosion affects various metals and the strategies used for its prevention and control. Test your knowledge on the ramifications of metal deterioration on safety and structural integrity.