Chapter 11 - Ceramics:

Inorganic, non-metallic compounds formed by heat. Examples:

Knife: Zirconium dioxide,

ZrO2

Rocket Nozzle: Silicone Nitride, Si3N4

Ball Bearing: Silicone Nitride, Si3N4

or Alumina Oxide or ZirconiaPorcelain high voltage insulator

Dental implants

Disk brake, silicone carbide

Ceramic inserts, cutting tools, tungsten carbide

See HO for Common Types

*See notes at bottom

III. Types of Ceramics:

I. Overview of ceramics:

Characterized by:

1. Compounds between metallic and non-metallic elements (i.e. Si and O, Si and N, Al and O, etc..)

2. Frequently oxides, nitrides and carbides (i.e. silicon carbide – SpinWorks)

3. Can be crystalline or amorphous

4. Very strong covalent (sharing of electrons) or ionic (transfer of electrons) bonds.

5. Properties include:

• Strong but brittle

• Low fracture toughness

• Good insulators of electricity BUT good conductor of heat (i.e. comparable to metals have reasonably high thermal conductivity, k) – this is unique to ceramics.

• Excellent high temp properties

• Low coef of thermal expansion

I. Nature of ceramics:

Example: Aluminum Oxide, Al2O3

Covalent = strong

Electrons tied up

II. Properties of Ceramics

• Benefits:

– High chemical resistance

– High melting point and therefore high operating T.

– Extremely hard and stiff (i.e. 180 E6 psi)

– Good electrical insulator (electrons tied up). Exception = superconductors

– Good thermal conductor (high K like metals)

– But, low thermal expansion and good thermal stability

– Good creep

– High modulus

– High compressive strength

II. Properties of Ceramics

• Shortcomings:– Low tensile strength and BRITTLE. Sut = Suc/10. Do not readily slip like metals

but fracture.– Catastrophic failure

• The bond is ionic and covalent. A material held by either type of bond will tend to fracture before any plastic deformation can occur!

– Low fracture toughness (1/10 to 1/100 KIC compared to metals)• Materials tend to be porous and microscopic imperfections act as stress concentration decreasing the

toughness further.

– Elongation = 0%– Low fatigue strength– Large statistical spread and less predictable than metals (size, shape and

location of internal flaws is likely to differ from part to part)– Prone to thermal shock– Hard to machine and form– Cost 8X more than metals– See Table 8.2

Optimized selection using charts

MρE1/2

23

MρE1/3

Results22 pass

Material 1 2230Material 2 2100Material 3 1950etc...

Ranked by Index /ρE1/2

1

MρE

Search area

Electrical Resistance:

Ceramics = good electrical insulators, but…

Selection: one-property indices

Good conductors: metals and ceramics

Good insulators: polymer foams, cork, wood, cardboard….

Good thermal conductors!

III. Types of Ceramics: (see HO 6 – 10):

a) Structural (clay) and whiteware: bricks, pipes, floor and roof tiles, dinner ware, chinca, etc…

b) Refractory ceramics: kiln lingings, high T capability most are based on silicates (sand)

c) Glass, amorphous ceramic, most based on silica, SiO2

– Annealed glass– Tempered glass– Laminated glass

Go to HO pg 6!!

III. Types of Ceramics: (see HO 6 – 10):

d) Technical or engineering ceramics – 3 categories:

i. Oxides (alumina, zirconia) semiconductors

ii. Non-oxide (carbides, borides, nitrides) i.e. tungsten carbide cutting tools, silicone nitride ball bearings, silicone carbide furnace inserts.

iii. Cermits or composites – combination of metals and ceramics (powder metallurgy), combines high strength and hardness, thermal characteristic of ceramics with toughness of metals)

V. How to Strengthen: (see HO 4,5):

a) Flame polishing to reduce surface cracks

b) Close surface cracks use in compression (or compress with metal band)

c) Atom gun to fill in surface cracks (fires ions into cracks)

d) Reduce crystal size

e) Laminate or anneal (glass)

f) Combine materials to increase toughness (cermits)

V. Manufacturing – see HO• In situ – cement – mix

powder with water• Sintering based

methods

http://www.youtube.com/watch?v=69Y0VuOYqkU

WATCH!!!!

http://ceramicinjectionmolding.com/