Corrosion control

Question 1

For what purpose would a mechanic use sodium dichromate? Chromic Acid? Alodine?

Question 2

Uniform etch corrosion

Answer 2

Results from a direct chemical attack on. Metal surface and involves only the metal surface. General dulling rough and possible frosted appearance.

Question 3

Pitting corrosion

Answer 3

Most common on aluminum and magnesium alloys. White powdery deposit.

Question 4

Galvanic corrosion

Answer 4

Two dissimilar metals make electrical contact in the presence of an electrolyte.

Question 5

Metal concentration cells

Answer 5

The area of the metal in contact with the low concentration of metal ions will be anodized and corrode

Question 6

Oxygen concentration cells

Answer 6

An oxygen cell can develop at any point where the oxygen in the air is not allowed to diffuse into the solution.

Question 7

Active passive cells

Answer 7

Metals which depend on a tightly adhering passive film, usually an oxide for corrosion protection, such as corrosion resistant steel

Question 8

Inter-granular corrosion

Answer 8

Is an attack along the grain boundary of an alloy and commonly results from a lack of uniformity in the alloy structure.

Question 9

Exfoliation corrosion

Answer 9

Is an advanced form of inter granular. Where the surface grains. Of a metal are lifted up b the force of expanding corrosion products just below the surface.

Question 10

Filiform corrosion

Answer 10

Form of oxygen concentration cells corrosion. Occurs when. The relative humidity of the air is between 78 and 90 percent and the surface is slightly acidic. Can lead to inter granular corrosion

Question 11

Stress corrosion cracking

Answer 11

Is an inter granular cracking of the metal which is caused by a combination of stress and corrosion.

Question 12

Corrosion fatigue

Answer 12

Is caused by the combined effects of cyclic stress and corrosion. Occurs in two stages: damages the metal by pitting second stage propagation of the crack.

Question 13

Fretting

Answer 13

Two highly loaded surfaces which are not supposed to move against each other. However vibration may cause the surfaces to rub together resulting in an abrasive wear. Protective coating is removed.

Question 14

Corrosion

Answer 14

Is a natural phenomenon which attacks metal by chemical or electrochemical actions and converts it into a metallic compound such as a oxide, hydroxide, or sulfate.

Question 15

What are three things that allow corrosion to take place

Answer 15

1.) Presence of a metal that will corrode (Anode)
2.) presence of a dissimilar conductive material ( cathode) which has less tendency to corrode
3.) presence of a conductive liquid or electrolyte

Question 16

Oxidation

Answer 16

A corrosion reaction in which the corroded metal forms an oxide. Helps prevent further corrosion.

Question 17

Uniform surface corrosion

Answer 17

Is the most common form of corrosion and is caused be either direct chemical attack or electrochemical attack.

Question 18

Pitting corrosion

Answer 18

Is one of the most destructive and intense forms of corrosion. It can occur in any metals, but is the most common on metals that form a protective oxide films.

Question 19

Concentration cell corrosion

Answer 19

Is corrosion of metals in a metal to metal joint, corrosion at the edge of a joint even though the joined metals are identical.