Crossion

Question 1

What is crossion

Answer 1

A chemical reaction

metal is converted into a metallic compound such as an oxide, hydroxide or sulphate

Question 2

Corrosive attacks

Answer 2

The corrosion process involves two chemical changes. The metal that is attacked or oxidised undergoes an anodic change, whilst the corrosive agent is being reduced and undergoing a cathodic change.

Question 3

Alclad

Answer 3

Highly resistance to chemical attacks

Question 4

Steel corrosion

Answer 4

Red rust on the surface

Question 5

Aluminium crosion

Answer 5

White / grey powder

Question 6

Magnesium crosion

Answer 6

Grey powder with sever pitting

Question 7

Copper crosion

Answer 7

Green powder product

Question 8

How to stop copper crosion

Answer 8

Coated with nickel and tin

Question 9

Fill form corrosion

Answer 9

Worm like
Lead to intergranular 
Occurs in high humidity 
And when surface is slightly acid 
Removed using glass bead blasting material

Question 10

What metals don’t corrode

Answer 10

Nobel metals
Gold
Platinum

Question 11

What is a passive film

Answer 11

When a metal is tightly bound to the corroding metal that they form an invisible oxide film

Question 12

Active metal

Answer 12

Lose electrons easily
Magnesium and aluminium
Corrode easily

Question 13

Stop aluminium crosion

Answer 13

Anodised
Primed
Top coated with paint

Question 14

Stop steel brass and bronze crosion

Answer 14

Cadmium plating

Question 15

How to stop magnesium crosion

Answer 15

Chemical treatments and paint finishes

Question 16

Electrochemical attraction

Answer 16

More commonly known as galvanic action, the essential ingredients for this
type of corrosion are two dissimilar metals in the presence of an electrolyte.

Question 17

Microbiological corrosion

Answer 17

Microbial attack includes actions of bacteria, fungi or moulds

Question 18

Stress corrosion

Answer 18

Stress corrosion is an intergranular cracking of the metal which is caused by a combination of stress and corrosion.
Stresses cause my internal or external loads

Question 19

Influence factors of corrosion

Answer 19

Type of metal
Presence of a dissimilar, less corrodible metal (galvanic corrosion) Anode and cathode surface areas (in galvanic corrosion) Temperature
Heat treatment and grain direction
Presence of electrolytes (hard water, salt water, battery fluids etc.) Availability of oxygen
Presence of different concentrations of the same electrolyte Presence of biological organisms
Mechanical stress on the corroding metal
Time of exposure to a corrosive environment

Question 20

What environment cause stress crosion

Answer 20

Salt solutions Cause aluminium
Methyl alcohol hydrochloric acid cause titanium
Air magnesium

Question 21

Electrochemical reaction

Answer 21

When a chemical reaction is caused by an externally supplied current, as in electrolysis, or if an electrical current is produced by a spontaneous chemical reaction as in a battery

Question 22

Pitting crosion

Answer 22

Most common for aluminium and magnesium 
White powdery 
Starts on surface extends vertically 
Decrease strength
Starting point for intergranular corrosion

Question 23

Intergranular corrosion

Answer 23

attack along the grain boundaries of the metal with little or no indication on the surface

High-strength aluminium alloys like 2024 and 7075 can develop intergranular corrosion if they have been improperly heat-treated and are then exposed to corrosive environments

Question 24

Exfoliation corrosion

Answer 24

Advanced form of intergranular corrosion where the surface gains are lifted up by the force of expanding corrosion
Prone in wrought products

Question 25

Getting corrosion

Answer 25

vibration cause the surfaces to rub together, resulting in an abrasive wear known as fretting.
The protective film on the metallic surfaces is removed by the rubbing action. The continued rubbing of protective oxide film exposes fresh active metal to the atmosphere.
Can cause server pitting
Black ring around faster heads

Question 26

Microbiology corrosion

Answer 26

Fungl and mould
Aerobic or anergalnic corrosion
Can produce corrosive chemicals such as hydrogen sulfide Ammonia
Area must be completely removed

Question 27

Crevice corrosion

Answer 27

This is corrosion of metal in a metal-to-metal joint, and corrosion at the edge of a joint. Sealing of joints and gaps and use of protective coatings in the fraying surface area can reduce crevice corrosion.