Ceramic Material Science © 2013 Su-Jin Kim, GNU Ceramics ( 세라믹 ) Associate Professor Su-Jin KimSu-Jin Kim School of Mechanical Engineering Gyeongsang National

CeramicCeramicMaterial ScienceMaterial Science

© 2013 Su-Jin Kim, GNU© 2013 Su-Jin Kim, GNU

Ceramics( 세라믹 )

Associate Professor Su-Jin Kim

School of Mechanical EngineeringGyeongsang National University



Ceramic

Pottery Aerospace

Memory

Medical

Cutting



Ceramic

Properties: - Tm for glass is moderate, but large for other ceramics. - Small toughness, ductility; large moduli & creep resist.

Applications: - High T, wear resistant, novel uses from charge neutrality.

Fabrication - some glasses can be easily formed - other ceramics can not be formed or cast.



Ceramics

• Ceramics are compounds of metallic and non-metallic(O, N, C) elements.

• Bonding between atoms is ionic or covalent .



Classification of Ceramics

Various types of ceramics are:

• Silicon Si: Silica SiO2

• Oxids O: Alumina Al2O3, Zirconia ZrO2

• Carbides C: Tungstem carbides WC, Silicon carbide SiC

• Nitrides N: Cubic boron nitride cBN, Titanium nitride TiN, Sialon



Silicate Ceramics( 규산염 세라믹 )• Most common elements on earth are Si & O• SiO2 (silica) : The strong Si-O bonds lead to a high melting

temperature (1710°C) for this material• Quarz( 석영 ), Glass( 유리 ), Clay( 점토 ) …

SiO4 tetrahedron4-

Si4+

O2-



Crystalline: Quartz send( 규사 ), Rock crystal( 수정 )

Non-crystalline (amorphous): Glass ( 유리 )

Silica, SiO2



Alumina Silicate( 규산알미늄 ) Al2O3 SiO2 H2O

• Refractories( 내화벽돌 ) used in high temperature furnaces.

• Clay( 점토 ) adjacent layers are bound by van der Waal’s forces.

Al2O3%

T(°C)

1400

1600

1800

2000

20 40 60 80 1000

alumina+mullite

mullite3Al2O3-2SiO2

+ L

Liquid (L)

mullite + crystobalite

crystobalite+L

alumina+L



Oxides ( 산화물 ), O

• Excellent wear resistance (Vickers hardness 10 GPa)• High rigidity (Young’s ratio 300GPa)• High electric resistance (>1015Ωcm)• White color tone

• Ex) Alumina(Al2O3) Zirconia(ZrO2)



Alumina, Al2O3

• Powder Sintering

• Bauxite(Al2O3 H2O) Aluminum ingot



Zirconia, ZrO2

• High melting point (2700C), Low thermal conductivity (4.0 W/mK )

• Refractories for iron casting



Nitrides ( 질화물 ) N

• Cutting materials and hard coatings: TiN, SiN

• Hexagonal boron nitride, h-BN : a layered structure is a useful high-temperature (~900°C) lubricant

• Gallium nitride (GaN) : blue light LED



Cubic boron nitride, CBN

• CBN is widely used as an abrasive.• Insolubility in iron alloys at high temperatures. Tool for

cutting or grinding steel alloy.• High thermal conductivity and electrical resistivity.



Carbides ( 탄화물 ) C• Metal + Carbon C, Black color tone

• Tungsten carbides WC ( 초경 ) : Cutting tools

• Titanium carbide TiC : Cutting tools, CVD coating



Silicon Carbide, SiC

• Popular abrasive

• Carbon-fiber-reinforced silicon carbide (C/SiC)is used for brake discs

• Semiconductor: MOSFET



Diamond• SCD (Single Cristal Diamond) is covalent bonded single

crystal of Carbon C• It is hardest in the world but decompose in air at 973 K.• PCD (Poly Crystal Diamond) is used to cut aluminum

alloys, ceramics, and stone. But it is soluble in iron alloy to give carbides.



Graphite( 흑연 )• Graphite is a layered structure of carbon C.• Weak van der Waal’s forces between layers• Planes slide easily over one another – low

friction good solid lubricant



Carbon nanotubes• Sheet of graphite rolled into a tube, Ends capped with

fullerene hemispheres• It has high strength and electrical current-carrying capability.



Limestone( 석회암 ) CaCO3

• Application: Cement, Glass, Tile, Ceramic

• Gypsum( 석고 CaSO4 H2O) board for insulation & soundproofing



Ceramic Products

1. Structural: bricks, floor and roof tiles

2. Refractories: iron making crucible

3. Whitewares: tableware, pottery, bathroom

4. Special: implants, disk brake, bearing



Fine particle(Quartz, Clay, Feldspar) + wet state plasticity form dry state Sintering( 소결 ) by fire Porcelain

Porcelain ( 도자기 )



Powder Sintering ( 분말 소결 )

15 m



General properties of ceramics• Ceramics are brittle, have high compressive strength and

hardness at elevated temperatures, high elastic modulus, low toughness, low density, low thermal expansion, and low thermal and electrical conductivity.

1. Mechanical properties• Sensitivity to cracks, impurities and porosity• Strength in tension is lower than compressive strength.2. Physical properties• Low specific gravity and have high melting temperatures.



Mechanical properties• Consider to be linearly elastic and brittle.• Bulk formed glass has low strength(<40 MPa) due to

microcracks on the surface, but the strength of glass fiber is about 2 GPa stronger than steel.

• Low thermal conductivity and high electric resistance.• Thermal expansion coefficient is lower than metals and

plastics.• Optical properties can be modified by varying their

composition and treatment.



Stress-Strain ( 응력 - 변형율 )

• Room T behavior is usually elastic, with brittle failure

250

50

Str

ess

(M

pa

)

0.0008Strain

Glass

Aluminum oxide



Porosity ( 기공 )

• Porosity decreases modulus of elasticity and fracture strengths.

Volume fraction porosity

Mo

du

lus

of

ela

stic

ity (

GP

a)

Fle

xura

l str

en

gth

(M

pa

)0 0.1 0.2 0.3 0.4 0.5 0.6

200

100



• 3-point bend test to measure flexural strength & elastic modulus.

Flexural strength( 굴곡강도 )

FL/2 L/2

= midpoint deflection

cross section

R

b

d

rect. circ.

location of max tension

• Flexural strength: • Typical values:

Si nitrideSi carbideAl oxideglass (soda-lime)

250-1000100-820275-700

69

30434539369

Material fs (MPa) E(GPa)

22

3

bd

LFffs (rect. cross section)

(circ. cross section)3R

LFffs



Ex) Ceramic for Heat Engines

• Advantages: – Run at higher temperature– Excellent wear & corrosion

resistance– Low frictional losses– Ability to operate without a

cooling system– Low density

• Disadvantages: – Brittle– Too easy to have voids-

weaken the engine– Difficult to machine

• Possible parts – engine block, piston coatings, jet engines

Ex: Si3N4, SiC, & ZrO2



• Glass is non-crystalline (amorphous) NaO2CaO6SiO2

• Some elements replaced by MgO, Al2O3 and K2O• They are resistant to chemical attacks and ranked by

their resistance to acid, alkali or water corrosion.

Glass ( 유리 )

Si 4+

Na +

O 2 -



Glasses

suspended

Parison

Compressed air



Glass vs. Glass-ceramic



• Specific volume (1) vs Temperature (T):

• Glasses: - do not crystallize - change in slope in spec. vol. curve at glass transition temperature, Tg - transparent - no crystals to scatter light

• Crystalline materials: - crystallize at melting temp, Tm - have abrupt change in spec. vol. at Tm

Glass Properties

T

Specific volume

Supercooled Liquid

solid

Tm

Liquid(disordered)

Crystalline (i.e., ordered)

T g

Glass (amorphous solid)

Documents

Ceramic Material Science © 2013 Su-Jin Kim, GNU Ceramics ( 세라믹 ) Associate Professor Su-Jin KimSu-Jin Kim School of Mechanical Engineering Gyeongsang National