ceramics materials prop thermal and mechanical

Traditional and engineering ceramicsTraditional and engineering ceramics

Suranaree University of Technology October 2007

T. Udomphol

Chapter 1

Traditional ceramics Clay Silica Feldspar+ +

2322

2322

6..

6..

SiOOAlONa

SiOOAlOK2SiOOHSiOOAl 2232 2.2.

• Structural clay products : bricks,

sewer pipe, roofing tile

• EX: Triaxial bodies:Whiteware,

porcelain, chinaware, sanitary ware.

Reactions of a triaxial body



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Traditional ceramics

Triaxial whiteware chemical composition



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Chapter 1

Electron micrograph of an electrical

insulator porcelain (etched 10 s, 0oC,

40% HF, silica replica)

quartz Mullite needles

High silica glass



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Slip casting processMaster and plaster moulds

Fresh cast

Dry

Slip casting

Colour paintFire


http://www.lindawilsonceramics.co.za/3.html

Pottery

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Chapter 1


Slip casting processSlip casting process Sanitaryware

Slip casting in plaster moulds and demoulding

www.3emmegi.com


Slip preparation

in ball millOHOHCaSOOHCaSO Co

223

221

4

150

24 .2. + →

Hemihydrate plaster – produced from gymsum


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Chapter 1


Engineering ceramics • Contain more of pure compounds of oxides,

carbides, nitrides.

• Ex: Al2O3, Si3N4, SiC, ZrO2 , refractory

oxides

Mechanical properties of engineering ceramics


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Chapter 1


Engineering ceramics Alumina

• Refractory tubing

• High purity crucibles for high temp

• High quality electrical applications

(low dielectric loss and high resistivity)

• Spark plug insulator

Microstructure of sintered, powdered aluminium

oxide doped with magnesium oxide

Alumina tubes

www.sentrotech.com


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Chapter 1


Engineering ceramics Silicon nitride (Si3N4)

• Dissociate at T > 1800oC.

• Cannot be directly sintered � reaction bonding.

Silicon nitride for engineering applications

Silicon powder

N2 flow

nitriding

Microporous Si3N4

High strength

nonporous Si3N4

Hot pressing with

1-5%MgO

www.defazio-rotary.com


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Chapter 1


Engineering ceramics Silicon carbide (SiC)

• Hard refractory carbide.

• Form skin of SiO2 at high temp.

• Resistance to oxidation at high temp.

• Can be sintered 2100oC with 0.5-1%B.

• Fibrous reinforcement in ceramic-

matrix composite material.

SiC fibre reinforced Titanium matrix

www.stork.com


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Chapter 1


Engineering ceramics Zirconia (ZrO2)

• Polymorphic: tetragonal � monoclinic.

• Mixed with CaO, MgO and Y2O3 � Partially stabilized zirconia (PSZ).

1170oC

Volume expansion

Heat treatment Cubic structure

www.azom.com

Zirconia

Mechanical properties of ceramicsMechanical properties of ceramics


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Chapter 1

• Brittle

• High strength (varying from 0.7 – 7000 MPa)

• Better compressive strength than tensile (5-10 times)

refractory; porous ceramics; glasses<50

porcelains; steatite, cordierite; magnesia, polished

glasses;

50-100

impure and/or porous alumina; mullite; high-alumina

porcelains; reaction bonded silicon nitride and

carbide; glass ceramics

100-200

sintered pure alumina and SiC; tempered glass200-600

Hot Pressed structural ceramics such as silicon

nitride, silicon carbide, alumina; sintered tetragonal

zirconia and sialon; cemented carbides

600-1000

polycrystalline long ceramic fibres (Al2O3, SiC): 1-2

GPa, single crystal short ceramic fibres (Al2O3, SiC

whiskers): 5-20 GPa,

> 1000

MaterialsLevel of strength

(MPa)



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Deformation mechanisms

• Lack of plasticity due to ionic and covalent bonding (directional).

• Stressing of covalent crystal � separation of electron-pair

bonds without subsequent reformation� brittle

• Deforming of ionic single crystal (MgO or NaCl) shows

considering amount of plastic deformation under compressive

force. However ionic polycrystals are brittle due to crack formation

at grain boundaries.

NaCl structure showing slip on

the (110) plane [110] direction

or AA’ and on the (100) plane

[010] direction BB’



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Factors affecting strength of ceramics

Depending on amount of defects

� giving stress concentration

• Surface cracks

• Porosity

• Inclusions

• Excessive grain sizes

No plastic deformation during crack

propagation from defects � very brittle.

Note:

Fabrication

Should control

• chemical composition

• microstructure

• surface condition

• temperature

• environment



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Toughness of ceramics

• Low toughness due to covalent-ionic bonding.

• Using hot pressing, reaction bonding to improve toughness.

• Fibre-reinforced ceramic matrix composites.

Fracture toughness of ceramics



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Toughness of ceramics Example

A reaction-bonded silicon nitride has a strength of 300 MPa and a

fracture toughness of 3.6 MPa.m1/2, What is the largest-size internal

crack that this material can support without fracturing? Given Y = 1

( )( )

mma

MPa

mMPaKa

aYK

f

IC

fIC

µ

ππσ

πσ

8.451058.4

300

.6.3

5

2

2

2

2

=×=

==

=

−

Therefore the largest internal crack 2a = 91.6 µm


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Chapter 1

Transformation toughening of Partially Stabilized Zirconia (PSZ)

Zirconia

+ (CaO, MgO or Y2O3) PSZ (metal stable)

Sintering at 1800oC+rapid cooling to RT+

reheating at 1400oC to give fine precipitates


Tetragonal �� monoclinic

under stressing

Volume expansion



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Fatigue failure of ceramics

• Fatigue failure in ceramics is rare due to lack of

plastic deformation during cyclic loading.

Fatigue cracking of polycrystalline alumina under cyclic loading



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Abrasive property of ceramics

• Hard and brittle

• Used as cutting, grinding and polishing tools.

www.moldmakingtechnology.com

Ceramic grinding wheelsCeramic cutting tools

• Aluminium oxide

• Silicon carbide

• Titanium nitride

• Tungsten carbide

• Boron nitride

Thermal properties of ceramicsThermal properties of ceramics


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Chapter 1

• Low thermal conductivity

due to ionic-covalent

bonding � insulator.

• Also used as refractories

in metal, chemical and

glass industries.

Thermal conductivity of

ceramic materials



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Chapter 1

Ceramic refractory materials

• A mixture of ceramic compounds

• Low-high temperature strength

• Low bulk density (2.1-3.3 g.cm-3)

• Porosity � insulating

Refractory bricks (60% Al2O3)

for hot blast furnace

img.alibaba.com

Basic refractory

Acidic refractory

Mainly based on SiO2 and Al2O3

Mainly based on magnesia (MgO),

lime (CaO) and Cr2O3



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Acidic refractory Basic refractory

• Silica refractory has high

refractoriness, high mechanical

strength and rigidity at high

temperature.

• Fireclays (fine plastic clays +

flint + coarse clay or grog)

• High alumina refractories

contains 50-99% alumina,

giving higher fusion temperature

(more expensive than fireclay).

• Basic refractory consists of

mixtures of MgO, CaO and Cr2O3.

• High bulk density

• High melting point

• Good resistance to chemical

attack (basic slag, oxides)

• Ex 92-95% MgO used for lining

in basic-oxygen steelmaking

process


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Ceramic tile insulation for the space shuttle orbiter


• About 24,000 ceramic tiles (70%) of silica-fibre compound are

used for insulating external surface of space shuttle.


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Chapter 1

Ceramic tile insulation for the space shuttle orbiter


Microstructure of LI900 high-temperature

reusable surface insulation (HTRS)

• High temperature reusable surface

(HTRS) made from 90% silica fibres

and 10% empty space.

• Density = 0.144 g.cm-3

• Temp ~ 1260oC

media.nasaexplores.com

upload.wikimedia.org

Borosilicate coating

GlassGlass


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Chapter 1

• Transparency

• Hardness and strength

• Corrosion/chemical resistance

• Vacuumtight enclosure

• Insulator

Properties of glass

Blown glass

www.geocities.com

Tinted or heat-absorbed glass

www.arch.tu.ac.th

Definition of glass

• An inorganic and noncrystalline

material which maintains its

amorphous microstructure below its

glass transition temperature.

GlassGlass


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Chapter 1

Glass transition temperature (Tg)

• Unlike solidified metal, a glass

liquid does not crystallize but

follow an AD path.

Viscous Plastic Glassy

Temp (decrease)

• The faster cooling rate,

the higher values of Tg.Solidification of crystalline and amorphous

materials showing a change in specific volume

GlassGlass


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Structure of glass Glass forming oxide - SiO2

Si-O tetrahedron Ideal crystalline silica

(crystobalite)Simple silica glass with

no-long range order

GlassGlass


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Structure of glass Glass modifying oxides - Na2O, K2O, CaO, MgO

• Oxygen from Na2O breaks up

silica network, leaving oxygen

atoms with an unshared electron.

• Na+ or K+ ions fits into interstices

of network.

Network modified glass (soda-lime glass)

GlassGlass


T. Udomphol

Chapter 1

Structure of glass Intermediate oxides in glass - Al2O3 , Pb2O3

• Oxides such as Al2O3 or Pb2O3

cannot form glass network but

join into an existing network.

• Aluminosilicate glass

provides higher temperature than

common glass.

GlassGlass


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Chapter 1

Glass composition

• Silica glass

• Soda-lime glass

• Borosilicate glass

(Pyrex glass)

• Lead glass

No radiation damage

Reduced Tm ~ 730 oC

Low thermal expansion

Shielding from high

energy radiation

GlassGlass


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Chapter 1

Viscous deformation of glasses

• Glass remains its viscous

(supercooled) liquid above Tg.

Temp > Tg Viscosity

RTQ

oe+=ηη

η = viscosity of the glass

ηo = pre-exponential constant

Q = molar activation energy for

viscous flow

R = gas constant

T = absolute temperature

GlassGlass


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Chapter 1

Viscosity reference points

Working point

Softening point

Annealing point

Strain point

Viscosity = 104 poise (103 Pa.s) � fabrication

Viscosity = 108 poise � glass flows at an appreciate

rate under its own weight (and surface tension).

Viscosity = 1013 poise � relieving internal stresses

Viscosity = 1014.5 poise � glass is rigid with slow

rate of stress relaxation.

Note: glass are usually melt at temp relating to viscosity = 102 poise

GlassGlass


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Chapter 1

Example A 96 % silica glass has a viscosity of 1013 P at its annealing point of

940oC and a viscosity of 108 P at its softening point of 1470oC.

Calculate the activation energy in kJ/mol for the viscous flow of this

glass in this temperature range.

Tanneal = 940+273 = 1213 K, ηap =1013 P

Tsoftening = 1470+273 = 1743 K, ηap =108 P

RTQ

oe+=ηη

5

8

13

1010

1011exp ==

−=

spapsp

ap

TTR

Q

η

η

molkJQ

KK

Q

/382

1743

1

1213

1

314.8exp105

=

−=

GlassGlass


T. Udomphol

Chapter 1

Fabrications of glass

• Forming sheet and plate glass

• Blowing, pressing and casting of glass

• Float glass process � molten glass ribbon moves on the top of

molten tin in a reducing atmosphere.

• Remove glass sheet when the glass surface is hard enough �

then pass to annealing furnace called lehr to remove residual

stresses.

• For deep, hallow shapes like bottles, jars, light bulbs envelops.

• Blowing air to force molten glass into moulds.

• Pressing a plunger into a mold containing molten glass.

• Casting into open moulds.

GlassGlass


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Float glass process

GlassGlass


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a) Reheat , b) final blow stage of a glass blowing machine process

GlassGlass


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Pyrex glass • Borosilicate glass

• Low thermal expansion

• Inert to almost all materials with the exception of

hydrofluoric acid, hot phosphoric acid and hot alkalies.

2.0%Al2O3

13.0%B2O3

0.5K2O

4.0%Na2O

81%SiO2

Approximate composition

GlassGlass


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b) after centre has cooled.a) After surface has cooled from high

temperature near glass-softening temperature.

The surface cools first (by rapid air cooling) and contract while

the interior is warm, developing compressive on the surface and

tensile in the middle.

Tempered glass

GlassGlass


T. Udomphol

Chapter 1

Distribution of residual stresses across the

sections of glass thermally tempered and

chemically strengthend

Tempered glass

• Tempering effect increases

the strength (4 x stronger than

annealed glass.

• Has higher impact resistance

than annealed glass.

• Ex: Auto side window, safety

glass for doors.

GlassGlass


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Chapter 1

Laminated glass

• Plastic interlayer (PVB-poly vinyle butyral)

is sandwiched with floated/annealed glass.

• Safety glass: Breaking like a spider web.

Laminated glass

www.dupont.com

Spider web breaking pattern

http://en.wikipedia.org/

GlassGlass

T. Udomphol

Chapter 1

Laminated glass

www.goodandquickglass.comSuranaree University of Technology October 2007

GlassGlass

T. Udomphol

Chapter 1

Chemical strengthened glass


• Submerging sodium aluminosilicate glass in a bath containing a

potassium salt at T~ 450-500oC for 6-10 h.

• Replacing Na ions with

larger K ions on the glass

surface.

Producing thin

compressive stresses at

the surface and tensile

stresses in the centre.

Distribution of residual stresses across the section of glass

thermally tempered and chemically strengthened.

Used in supersonic aircraft glazing,

ophthalmic lenses.

ceramics materials prop thermal and mechanical

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