Chapter 2 - Corrosion Flashcards
Define corrosion?
The deterioration of a substance usually metal from a reaction with its environment.
What is passivation?
A layer of oxides formed on the surface of a metal that provides corrosion protection for example stainless steel
What are the elements of a corrosion cell?
Anode, cathode, metallic pathway and electrolyte.
Describe what happens at the anode.
The anode is a part of the metal that corrodes (dissolves) in the electrolytes it does so in the form of positively charged ions.
What is the function of the electrolyte?
Allows the passage of ions to connect the corrosion cell
What is the function of the metallic pathway?
Allows the flow of electrons to connect the corrosion cell
What is the galvanic series?
The galvanic series if the list of materials in order of their corrosion potential with most easily corroded at the top and lease corroded at the bottom.
A listing of metals in order of reactivity( more or less noble) in seawater at 25C.
List 3 most easily(active) corroded materials.
Magnesium, zinc ,aluminum.
List 3 least easily( active) corroded materials.
Platinum, gold, silver.
The general rule of galvanic corrosion are?
When dissimilar metals are connected, the most active (or anodic) metal corrodes more rapidly.
The less noble( or more reactive ) metal when connected to a more noble ( or less reactive metal) will corrode preferentially.
Name the five most important factors that affect the rate of corrosion.
Humidity, oxygen, chemical salts, pollutants and temperature
General corrosion is?
Relatively uniform loss of material over the entire surface.
A general thinning of the affected surface.
Easy to inspect.
Does not cause catastrophic failures.
Localized corrosion is
Corrosion that occurs at discrete sites on the metal surface.
Corrode in areas difficult to inspect
Less common in atmospheric exposure than in immersion or splash/spray exposures.
Typically pitting and crevice corrosion
It is typically of the most concern as damage is concentrated and loss of integrity or structural failure can result.
List some of the common tools /methods used for corrosion control.
Design, inhibitors, material selection, catholic protection, protective coatings, splash zone system and alteration of the environment.
