Galvanic Series and Corrosion Types

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Questions and Answers

What is the primary difference between the corrosion of ceramic materials and metallic materials?

Ceramic materials corrode through dissolution, whereas metallic materials corrode through electrochemical processes.

What is the purpose of cathodic protection in steel pipes and ships' propellers?

To prevent corrosion by using a more reactive metal such as Mg or Zn to sacrificially corrode instead of the steel or copper.

What is the result of covalent bond rupture in polymer degradation?

A reduction in mechanical integrity due to the severance of molecular chain bonds.

What is the primary mechanism of galvanic corrosion?

The electrochemical reaction between two dissimilar metals, resulting in the oxidation of the more reactive metal. Signup and view all the answers

What is the purpose of bluing in steel treatment?

To produce a dark protective layer of magnetite, which protects the steel against oxidation. Signup and view all the answers

What is the primary difference between anodising and phosphating?

Anodising is used to strengthen the layer of oxide on aluminium, while phosphating is used to create a protective layer on steel. Signup and view all the answers

What is the role of the galvanic series in predicting the corrosion behavior of metallic materials?

The galvanic series ranks the tendency of metallic materials to corrode when coupled to other metals, with more reactive metals at the top and less reactive metals at the bottom. Signup and view all the answers

What is the primary mechanism of swelling in polymer degradation?

The absorption of small solute molecules into the polymer, causing the macromolecules to expand and swell. Signup and view all the answers

What is the ranking of metals/alloys in terms of reactivity in seawater called?

Galvanic series Signup and view all the answers

What type of corrosion occurs along grain boundaries in alloys under specific conditions?

Intergranular corrosion Signup and view all the answers

What is the process by which atomic hydrogen penetrates into a metal alloy, reducing its ductility and tensile strength?

Hydrogen embrittlement Signup and view all the answers

What is the primary method for preventing corrosion in a metal alloy?

Choosing the right metal for the working environment Signup and view all the answers

What should be avoided in order to prevent galvanic corrosion?

Dissimilar metals Signup and view all the answers

What should be provided to account for corrosion of thickness?

An allowance Signup and view all the answers

Why is welding preferred over riveting in corrosion prevention?

To prevent crevices and minimize galvanic corrosion Signup and view all the answers

What type of metals are self-protecting?

Metals that form a protective oxide layer Signup and view all the answers

What is the effect of lowering the fluid temperature on the corrosion rate of a metal?

It slows down the corrosion rate by reducing the kinetics of oxidation and reduction. Signup and view all the answers

How do inhibitors prevent corrosion?

They slow down oxidation and reduction reactions by removing reactants or attaching species to the surface. Signup and view all the answers

What is the purpose of cathodic protection in preventing corrosion?

It attaches a more anodic material to the one to be protected, thereby reducing the corrosion rate. Signup and view all the answers

What is the difference between metal coatings via electrolysis and immersion in molten metal?

Electrolysis involves applying an electrical voltage to deposit a layer of metal, while immersion in molten metal involves dipping the piece in a bath of molten metal. Signup and view all the answers

What is the purpose of nickel plating in preventing corrosion?

It provides a protective layer of nickel on the surface of the metal, thereby reducing the corrosion rate. Signup and view all the answers

What is the significance of alternating layers of Cu, Ni, and Cr in metal coatings?

These layers provide a protective coating that prevents corrosion, with each layer having a specific role in preventing corrosion. Signup and view all the answers

What is the difference between galvanizing and tinplating?

Galvanizing involves immersing the piece in a bath of molten zinc, while tinplating involves coating the piece with a layer of tin. Signup and view all the answers

Study Notes

Galvanic Series

Ranks the reactivity of metals/alloys in seawater, showing the cathodic and anodic relationships between metals.
Lists the metals/alloys from most noble (least reactive) to most active (most reactive):
- Platinum
- Gold
- Graphite
- Titanium
- Silver
- 316 Stainless Steel
- Nickel (passive)
- Copper
- Nickel (active)
- Tin
- Lead
- 316 Stainless Steel
- Iron/Steel
- Aluminum alloys
- Cadmium
- Zinc
- Magnesium

Corrosion Types

Intergranular Corrosion: Corrosion occurs along grain boundaries for alloys in specific conditions, leading to failure.
Hydrogen Embrittlement: Reduction in ductility and tensile strength of metal alloys (e.g., steels) due to atomic hydrogen penetration.

Corrosion Prevention

Materials Selection and Design: Choose the right metal for the working environment, avoiding dissimilar metals and ensuring corrosion allowance.
Environment: Change the environment to reduce corrosion (e.g., lower temperature, pressure, concentration, and velocity).
Add Inhibitors: Remove reactants or attach species to the surface to slow oxidation/reduction reactions.
Cathodic (or Sacrificial) Protection: Attach a more anodic material to the one to be protected.

Anticorrosion Treatments

Metal Coatings: Via electrolysis, immersion in molten metal, metallizing, case hardening, and plating.
Non-Metallic Coatings: Inorganic (enamel, phosphating, anodizing, bluing) and organic (paints).

Corrosion of Non-Metals

Ceramic Corrosion: Involves dissolution, with ceramic materials frequently used due to their resistance to corrosion.
Polymer Degradation: Deterioration by environmental interactions, including swelling, dissolution, and bond rupture.

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Description

This quiz covers the Galvanic Series, ranking the reactivity of metals and alloys in seawater, and different types of corrosion. It's essential for understanding the chemical reactions between metals and their environment.