Corrosion Basics and Components

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Questions and Answers

What is the primary reason metals undergo corrosion?

Metals are good conductors of electricity.

Metals are in their natural state.

Corrosion is beneficial to metals.

Metals want to return to their ore form. (correct)

Which component of corrosion is responsible for losing electrons?

Electrolyte

Anode (correct)

Electrical Path

Cathode

What is meant by the term 'degradation' in materials?

The responsible breakdown of metals into oxides.

The enhancement of a material's properties.

The process of rust formation.

The loss of properties in polymers and ceramics. (correct)

Which of the following best describes the role of the cathode in corrosion?

It remains intact and is protected during the process. Signup and view all the answers

In electrochemical corrosion, what is required for the flow of electrons?

Anode and a salt bridge. Signup and view all the answers

Which of the following statements about plastics in relation to corrosion is true?

Plastics do not corrode like metals. Signup and view all the answers

What type of reaction is involved in the corrosion process of metals?

Oxidation-reduction reaction Signup and view all the answers

What is the purpose of the electrolyte in the corrosion process?

To conduct electrical current. Signup and view all the answers

What is the effect of a pH level below 7 on corrosion?

It accelerates the corrosion process. Signup and view all the answers

How does temperature influence corrosion rates?

Each 10°C increase in temperature can double corrosion activity. Signup and view all the answers

What role do inhibitors play in corrosion prevention?

They decrease the corrosiveness of the environment. Signup and view all the answers

What is the function of protective coatings in corrosion control?

To provide corrosion-resistance and protect against chemicals. Signup and view all the answers

How does mechanical stress relate to corrosion?

It can open small cracks and accelerate corrosion. Signup and view all the answers

What is a common result of corrosion occurring in metals?

It significantly reduces the strength of the metals. Signup and view all the answers

What kind of environment can promote corrosion due to dew saturation?

An environment with high salt content Signup and view all the answers

What is the nature of corrosion as an electrochemical process?

It involves the transfer of electrons between a metal surface and an aqueous electrolyte. Signup and view all the answers

What occurs when two dissimilar metals are placed in contact with each other in the presence of an electrolyte?

Galvanic corrosion occurs Signup and view all the answers

Which of the following metals is considered anodic when paired with copper in the described scenarios?

Aluminum Signup and view all the answers

What is the primary consequence of stress corrosion cracking?

Spontaneous cracking Signup and view all the answers

In a galvanic series, which condition describes a greater corrosion potential?

Metals further apart in the series Signup and view all the answers

At what temperatures is stainless steel particularly prone to stress corrosion cracking in chloride solutions?

Between 50°C-60°C Signup and view all the answers

Which metal alloy is likely to experience stress corrosion cracking in ammonia atmospheres?

Copper alloys Signup and view all the answers

What type of solution can cause steel to crack due to stress corrosion?

Chloride solutions Signup and view all the answers

Which pair of metals would likely show little effect on each other when in contact?

304 stainless steel and 316 stainless steel Signup and view all the answers

What is the main reason cadmium plating is being replaced in industrial use?

It is more expensive than zinc coatings. Signup and view all the answers

Which property of chromium plating makes it suitable for contact with foodstuffs?

Resistance to corrosion and heat Signup and view all the answers

Which of the following is a major application of tin plating?

Protection of electrical components Signup and view all the answers

What is a significant drawback of using zinc coatings on items meant for food contact?

They can dissolve in dilute acids and alkalis. Signup and view all the answers

What must be avoided when using cadmium plating in terms of temperature?

Temperatures exceeding 250°C Signup and view all the answers

What is the primary function of paints used in industrial applications?

To enhance corrosion-resistance Signup and view all the answers

Nickel plating is primarily known for its use as a:

Base layer for chromium plating Signup and view all the answers

Which of the following is an application where galvanizing is mainly used?

Heavy industrial machinery Signup and view all the answers

What is the primary function of primer in a paint system?

To adhere strongly and prevent corrosion Signup and view all the answers

Which type of paint is known for its outstanding resistance to water penetration?

Chlorinated-rubber paints Signup and view all the answers

What is a key characteristic of epoxy-resin-based paints?

They provide high chemical resistance. Signup and view all the answers

What role do sacrificial anodes play in cathodic protection?

They prevent corrosion on less active materials. Signup and view all the answers

Which metals are commonly used for sacrificial anodes?

Zinc, magnesium, and aluminum Signup and view all the answers

What type of corrosion is most commonly associated with pipes made from different metals?

Galvanic corrosion Signup and view all the answers

Why should sacrificial pipe sections be routinely inspected?

To check for premature wear and corrosion Signup and view all the answers

Which advantage is NOT associated with acrylic paints?

They provide superior flexibility. Signup and view all the answers

Study Notes

Corrosion

The tendency of metals to return to their original state, usually as metal oxides.
Occurs when metals react with oxygen in an oxidation-reduction reaction.
Deterioration of a material due to reaction with its environment.

Components of Corrosion

Anode: Where corrosion occurs.
- Releases positively charged metal ions into the electrolyte.
- Electrons are left behind in the metal and flow to the cathode.
- Oxidation (loss of electrons) takes place at the anode.
Cathode: The part of the metal where electrons flow.
- Remains intact and protected.
- Reduction takes place at the cathode.
Electrolyte: A solution capable of conducting electrical current (e.g., moisture or salt solution).
Electrical Path: A connection between the anode and the cathode, allowing electron flow.

Types of Corrosion

Galvanic Corrosion: Occurs when two dissimilar metals are in contact in the presence of an electrolyte.
- The more anodic metal corrodes, while the more cathodic metal remains intact.
- The further apart the metals are in the galvanic series, the greater the corrosion difference.
Stress Corrosion Cracking: Cracking of a material under static stress due to corrosion.
- Occurs in many plastics, aluminum alloys, copper alloys, magnesium alloys, carbon steels, stainless steels, titanium alloys, and others.
- High applied or residual stresses increase the likelihood of stress corrosion cracking.
Atmospheric Corrosion:
- Moisture: Condensation and dew can create an aggressive electrolyte environment that promotes corrosion.
- Chemicals: Acids in the atmosphere accelerate corrosion.
- Temperature: Every 10°C increase in temperature can double corrosion activity.
- Mechanical Stress: Stress can exacerbate corrosion by opening up small cracks.

Prevention and Control

Inhibitors: Substances that, when added in low concentrations, decrease the corrosiveness of the environment.
- Specific inhibitors depend on the alloy and the corrosive environment.
- Examples: Hydrazine in boiler feed water, nitrite in cooling systems.
Protective Coatings:
- Electroplating: Common coatings used for corrosion resistance, wear resistance, and decorative purposes.
  - Cadmium plating: Excellent corrosion resistance, especially in marine applications, but toxic.
  - Chromium plating: Widely used for corrosion, wear, and heat resistance, as well as decorative purposes.
  - Nickel plating: Used as a base for chromium plating, provides wear and corrosion resistance.
  - Tin plating: Used for products in contact with foodstuffs, protects against corrosion and aids soldering.
  - Zinc coating: Galvanizing is a hot-dip process used for industrial and construction applications.
- Paints: Provide corrosion resistance and a decorative finish.
  - Chlorinated-rubber paints: Excellent chemical resistance and water penetration resistance.
  - Acrylic paints: Fast drying, tough, and durable, widely used in vehicle applications.
  - Epoxy resins: Used for high chemical resistance.
Cathodic Protection:
- Sacrificial Anodes: Highly active metals (e.g., magnesium, zinc, aluminum) used to prevent corrosion of a less active material.
  - The anode is consumed instead of the material being protected.
- Galvanic Corrosion Control: Sacrificial pipe sections can be used to concentrate corrosion in specific areas.
  - Zinc and aluminum are preferred metals for marine industry pipelines.

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Description

This quiz explores the fundamental concepts of corrosion, including the roles of anodes, cathodes, and electrolytes. Participants will learn about different types of corrosion and the processes involved in metal deterioration. Test your understanding of how these components interact in electrochemical reactions.