15. Corrosion of metals

Question 1

____ _____ is the degradation of one or more material properties due to exposure to its surrounding environment.

Answer 1

Environmental degradation

Question 2

______ refers to the continued (unchecked) electrochemical attack of a material, normally resulting in oxidation of that metal.

Answer 2

Corrosion

Question 3

Corrosion typically converts a refined metal to a more ____-____ form found in the environment.

Answer 3

chemically-stable
or
thermodynamically-stable

Question 4

What is the driving force for corrosion

Answer 4

a reduction in energy

Question 5

The anode is where _____ occurs.

Answer 5

oxidation

Question 6

The cathode is where _____ occurs.

Answer 6

reduction

Question 7

What 4 things does corrosion require?

Answer 7

1. Reduction in energy: thermodynamic driving force
2. Water or moisture to act as a medium for ion conduction and ionic transport
3. Source of oxidant (normally O2, sometimes sulfur)
4. Mass transport of oxidant to the metal surface

Question 8

What are the two conditions for galvanic corrosion?

Answer 8

(1) two different metals or alloys are electrically coupled while (2) exposed to an electrolyte

Question 9

In galvanic corrosion, the more reactive metal is _____ (oxidized/reduced) and acts as the _____ (anode/cathode); it corrodes.

Answer 9

oxidized

anode

Question 10

The less reactive metal is _____ (oxidized/reduced) and acts as the _____ (anode/cathode); it is protected.

Answer 10

reduced

cathode

Question 11

What are the 3 general methods for corrosion protection

Answer 11

1. Self-driven formation of a protective oxide
2. Physical barriers (paint, noble coating)
3. Sacrificial or cathodic protection

Question 12

Describe how self Formation of a protective oxide layer prevents corrosion

Answer 12

For some metals or alloys, a protective oxide coating forms upon initial exposure to oxygen which prevents against further corrosion. This only occurs if the oxide adheres to the surface and is dense enough to limit
oxygen transport to the interior.

Question 13

Describe how noble coating prevents corrosion

Answer 13

The main metal is coated with a less chemically active metal layer which protects the metal underneath

Question 14

Desribe how sacrificial or cathodic coating prevents corrosion

Answer 14

The main metal is coated with a more chemically active metal which corrodes away while the main metal underneath remains uncorroded.