Chapter 12: Structures & Properties of Ceramicsma.gnu.ac.kr/course/ms/10_Ceramic.pdf ·  · 2017-04-06Ceramic Crystal Structures Ceramics high temperature, hardness, ... (Quartz,

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Ceramics (세라믹)

Associate Professor Su-Jin Kim

School of Mechanical Engineering

Gyeongsang National University

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

OCW

Ionic crystal structures

https://youtu.be/A3cPHn_OgVQ?list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm

Ceramic Crystal Structures

https://youtu.be/JILO8IppZis

Ceramics high temperature, hardness, chemical stable > brittle

https://youtu.be/9DopxIV4Css

Space Shuttle Heat Protection

https://youtu.be/oZg3x7yy80o

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

OCW

Cement and Concrete

https://youtu.be/woaUs5XnjUo

Glass (MIT kids 5min)

brittle, crack, rapid cooling, compressive stress on surface

https://youtu.be/1VrdUYbHvyo

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

KOCW

세라믹 결정구조

http://www.kocw.net/home/cview.do?lid=0f4393f1fb61cdd3

세라믹, 유리, 탄소, 강도시험

http://www.kocw.net/home/cview.do?lid=2f87428d88f9a817

세라믹스의 분류 및 활용 http://www.kocw.net/home/cview.do?lid=a0d249cb4b34f91b

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Ceramic

Pottery Aerospace

IC Medical Cutting

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

• Bonding between atoms is ionic or covalent .

Glass

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• Ionic bonding, Covalent bonding.

Ceramic Bonding

SiC: Covalent

CaF2: Ionic

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Ionic Bonding & Structure

• Ionic bonding

• Ionic radius - stable structures

- -

- - +

unstable

- -

- - +

stable

- -

- - +

stable

+ - e-

ZnS

NaCl

CsCl

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

General properties of ceramics

• High melting temperature

• High hardness (wear resistance)

• Chemical stability

• Electrical & thermal insulator

• Brittle (linear elastic)

• Compression strength >> Tension (sensitive to crack)

• Low thermal expansion

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Stress-Strain (응력-변형율)

• Room T behavior is usually elastic, with brittle

failure

250

50

Str

ess (

Mpa)

0.0008 Strain

Glass

Aluminum oxide

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Porosity (기공) Strneggth (강도)

• Porosity decreases modulus of elasticity and

fracture strengths.

Volume fraction porosity

Modulu

s o

f ela

sticity (

GP

a)

Fle

xura

l str

ength

(M

pa)

0 0.1 0.2 0.3 0.4 0.5 0.6

200

100

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• 3-point bend test to measure flexural strength &

elastic modulus.

Flexural strength(굴곡강도)

F L/2 L/2

d = midpoint

deflection

cross section

R

b

d

rect. circ.

location of max tension

• Flexural strength: • Typical values:

Si nitride

Si carbide

Al oxide

glass (soda-lime)

250-1000

100-820

275-700

69

304

345

393

69

Material s fs (MPa) E(GPa)

22

3

bd

LFffs s (rect. cross section)

(circ. cross section) 3R

LFffs

s

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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) …

SiO 4 tetrahedron 4-

Si 4+

O 2 -

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Non-crystalline (amorphous): Glass (유리)

Silica, SiO2

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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 80 100 0

alumina

+mullite mullite 3Al2O3-2SiO2

+ L

Liquid (L)

mullite + crystobalite

crystobalite+L

alumina+L

SiO2

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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)

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Alumina, Al2O3

• Powder Sintering

• Bauxite(Al2O3 H2O) Aluminum ingot

https://youtu.be/H7TuwEUAhAI

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Zirconia, ZrO2

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

• Refractories for iron casting

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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.

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Carbides (탄화물) C

• Metal + Carbon C, Black color tone

• Tungsten carbides WC (초경) : Cutting tools

• Titanium carbide TiC : Cutting tools, CVD coating

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Silicon Carbide, SiC

• Popular abrasive

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

• Semiconductor: MOSFET

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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.

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Carbon nanotubes

• Sheet of graphite rolled into a tube, Ends capped with fullerene hemispheres

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Limestone(석회암) CaCO3

• Application: Cement, Glass, Tile, Ceramic

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

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

Porcelain (도자기)

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Powder Sintering (분말 소결)

15 m

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• 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 -

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Glass vs. Glass-ceramic

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Glass Properties

• Easy processing (medium melting temperature)

• Transparent

• High hardness

• Corrosion resistance

• Fragile(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.

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• 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

Specific volume vs Temperature

T

Specific volume

Supercooled Liquid

solid

T m

Liquid (disordered)

Crystalline (i.e., ordered)

T g

Glass

(amorphous solid)

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• Viscosity decreases with T

• Impurities lower Tdeform

Glass Viscosity(점도) vs. T and Impurities V

isco

sity [P

a ×

s

]

1

10 2

10 6

10 10

10 14

200 600 1000 1400 1800 T(°C)

T deform : soft enough

to deform or “work”

annealing range

Tmelt

strain point

• fused silica: > 99.5 wt% SiO2

• soda-lime glass: 70% SiO2

balance Na2O (soda) & CaO (lime)

• Vycor: 96% SiO2, 4% B2O3

• borosilicate (Pyrex):

13% B2O3, 3.5% Na2O, 2.5% Al2O3

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Brittle Fracture (취성 파괴)

• Micro cracks amplify tensile stress Low fractural

strength & tensile strength.

Fracture surface of glass rod

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

• Annealing: --removes internal stress caused by uneven cooling.

• Tempering: --puts surface of glass part into compression

--suppresses growth of cracks from surface scratches.

--sequence:

Heat Treating Glass

further cooled

tension

compression

compression

before cooling

hot

surface cooling

hot

cooler

cooler

--Result: surface crack growth is suppressed.

Ceramic

Material Science

© 2013 Su-Jin Kim, GNU

Beaker Green house glass Display cover

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