5 - Corrosionof Non-Metals

Question 1

Types of non-metallic corrosion

Answer 1

CHEMICAL REACTION CORROSION , PHYSICAL INTERACTION CORROSION

Question 2

It is the corrosion of a polymer main chain

Answer 2

Chain scission

Question 3

Causes/ Sources of Chain scission

Answer 3

• Heat: Chain scission will occur when polymers are exposed to heat
  above a specified temperature limit
• UV Radiation: In the presence of oxygen, UV-radiation can cause a
  breakdown of the polymer chains.

Question 3

Type of corrosion where the polymer gets weakened from the addition of water at an elevated temperature.

Answer 3

Hydrolysis

Question 3

Corrosion of nonmetallic materials
caused by their interaction with the environment.

Answer 3

PHYSICAL INTERACTION CORROSION

Question 3

Mechanisms of attack on plastics (6)

Answer 3

• Disintegration or degradation: absorption, permeation or solvent action of plastic

-Oxidation, where chemical bonds are attacked

-Hydrolysis, where ester linkages are attacked

-Radiation

-Thermal degradation involving depolymerization
and possibly repolymerization

• Dehydration

Question 3

The
penetration of the
plastic by a corrodent,
which causes
softening, swelling, and
ultimate failure

Answer 3

Solvation

Question 4

Molecular migration through microvoids
either in the polymer or between polymer molecules.

Answer 4

Permeation

Question 5

Type of corrosion resulted by polymer absorption of corrodents such as organic liquids.

Answer 5

Swelling and softening of the polymer

Question 6

True or false:
When compared to steel and plastic polymers, technical ceramics
offer superior corrosion resistance.

Answer 6

True

Question 7

TRUE or FALSE: Ceramic Materials have weak chemical resistance

Answer 7

False

Question 8

The form of corrosion in ceramics that takes place as a result of chemical
dissolution.

Answer 8

Uniform corrosion :
The corrosion product
formed is nonprotective, being
either poorly adherent, soluble, or
a good transport medium for the
corrodent to the ceramic face

Question 9

Factors affecting Ceramic Deterioration

Answer 9

-Frost: Damage can occur when
ceramics are exposed to
freezing temperatures
and frost

-Mold Growth: Occurs on high humidity

-Impact and abrasion

-Water can dissolve or
deform ceramics that have
been low fired, at temperatures around
600°C.

-Soluble salts:
The crystallization/dissolution of soluble salts within and on the ceramic pores causes a cycle of expansion and compression, damaging the ceramic structure.

Question 10

Materials made from a
polymer matrix that is
reinforced with an engineered,
man-made or natural fiber or other
reinforcing material.

Answer 10

Composites

Question 11

Modes of Failures of Polymetric Materials

Answer 11

Plastic Deformation
Crazing
Fatigue
Thermal and Residual Stress
Physical aging
Moisture effect
photodegradation
Chemical Attack

Question 12

True or False:
Plastic deformation is reversible and returns to its original shape after removing the applied forces

Answer 12

FALSE

Question 13

A Network of visual cracks formed on high-impact plastics due to the combined
effect of stress and
aggressive environment

Answer 13

CRAZING; a polymer
develops extensive shear banding beyond
the elastic limit and undergoes
considerable permanent strain (crazing) before fracture.

Question 14

A failure mechanism originating from prolonged cyclical stresses resulting in eventual failure or tear.

Answer 14

FATIGUE

Question 15

A significant phenomenon among polymers characterized by changes in material properties over time due to molecular relaxations, becoming brittle.

Answer 15

AGING; the aging process occurs below glass transition
temperature (Tg)

Question 16

Fracture or formation of cracks in brittle materials that occurs when the release rate of stored energy in the material exceeds the amount of energy released due to the increase of surface area that occurs in crack formation.

Answer 16

Crack branching