Topic 8 - Corrosion

Corrosion

loss of material (like erosion)

Electrochemical degradation

a process in metals that leads to corrosion

OIL RIG

Oxidation is Lose (an e-), Reduction is Gain (an e-)

Anode

site of oxidation where loss of electrons occurs

Cathode

site of reduction where gain of electrons occurs

Electrolyte

the electrically conductive medium in which the Anode and Cathode reside

Potential Difference

a voltage difference that must exist between the Anode and Cathode

Galvanic Corrosion

occurs when two dissimilar metals are immersed in a conductive solution and are electrically connected

EMF

Electromotive Force, a metal's ranking in respect to reactivity

Uniform attack

evenly distributed corrosion

Pitting Corrosion

localized corrosion producing cavities/holes in a metal

Crevice Corrosion

attack of metal surface by a stagnant solution in crevices

Intergranular Corrosion

corrosion along grain boundaries due to depletion

Stress Corrosion

corrosion at grain boundaries affected by tensile stress causing cracks

Hydrogen Embrittlement

absorption of diffusible hydrogen harmful to the toughness of steel

Corrosion Prevention

methods to prevent corrosion, including paint and epoxy

Passivation

formation of a protective oxide barrier under certain conditions

Sacrificial Anode

a method where a more reactive metal is used to protect another metal from corrosion

Rust

an example of oxidation involving iron in water containing dissolved oxygen

Zinc oxidation reaction

Zn → Zn2+ + 2e-

Iron oxidation reaction

Fe + ½O2 + H2O → Fe2+ + 2OH- → Fe(OH)2

Iron Hydroxide reaction

2Fe(OH)2 + ½O2 + H2O → 2Fe(OH)3

Iron oxide reaction

2Fe(OH)3 → Fe2O3 + 3H2O

Corrosive Environments

conditions that promote corrosion, such as moisture and sulfur