Material Corrosion (up to pg108) Flashcards
What is the Galvanic Series?
A list of elements ranked by reactivity in seawater. The higher a material is, the less reactive and more cathodic.
Why do most metals appear in nature either ionically or in alloys?
As they are more stable in these states. Since oxidation is loss there is a net decrease in free energy when metals are oxidised, making them less reactive and more stable.
What is passivity?
When some materials appear twice in the Galvanic Series as a result of particular environmental conditions where they lose their reactivity and become extremely inert.
What is thought to cause passivity?
The formation of a very thin and highly adherent protective film on the surface of the metal that protects it from degradation.
How can cold working effect liability to corrode?
Cold worked materials are more liable to corrode than the same one in an annealed state.
What are the three main environmental variables to take into account for corrosion?
Water velocity, pH and temperature
When may increased acidity not result in an increased corrosion?
When it is on an element that experiences passivity, as it may trigger the formation of the oxide layer and thus the extreme reduction in reactivity.
What are the 8 forms of metallic corrosion?
Uniform, galvanic, crevice, pitting, intergranular, selective leaching, erosion-corrosion and stress corrosion
What is uniform attack?
When the whole surface area is attack evenly. Most common type of corrosion and planned for easily. Often leaves behind scale or deposits.
What is galvanic corrosion?
When two materials are coupled while exposed to an electrolyte, allowing for the more reactive of the two to sacrifice itself whilst the other does not react
How can one reduce galvanic corrosion?
Choosing a coupling of two metals close to each other in the Galvanic Series, use a large anode area, electrically insulate dissimilar metals, connect a third anodic material to the other two to protect them
