chapter 12,13: ceramics - 중앙대학교 시스템 융합설계 연구실...

Chapter 12 -

Chapter 12,13: Ceramics

School of Mechanical Engineering Choi, Hae-Jin

Materials Science - Prof. Choi, Hae-Jin 1

http://www.cau.ac.kr/

Chapter 12 - 2

ISSUES TO ADDRESS...

• How do the crystal structures of ceramic materials differ from those for metals?

• What types of defects arise in ceramics?

• What types of failures exists in ceramics?

• How do we classify ceramics?

• What are some applications of ceramics?


Chapter 12 - 3

• atoms pack in periodic, 3D arrays Crystalline materials...

-metals -many ceramics -some polymers

• atoms have no periodic packing Noncrystalline materials...

-complex structures -rapid cooling

crystalline SiO2

noncrystalline SiO2 "Amorphous" = Noncrystalline Adapted from Fig. 3.40(b), Callister & Rethwisch 3e.

Adapted from Fig. 3.40(a), Callister & Rethwisch 3e.

Materials and Packing

Si Oxygen

• typical of:

• occurs for:

Materials Science - Prof. Choi, Hae-Jin


Chapter 12 - 4

• Bonding: -- Can be ionic and/or covalent in character. -- % ionic character increases with difference in electronegativity of atoms.

Adapted from Fig. 2.7, Callister & Rethwisch 3e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.

• Degree of ionic character may be large or small:

Atomic Bonding in Ceramics

SiC: small CaF2: large



Chapter 12 - 5

Ceramic Crystal Structures

Oxide structures – oxygen anions larger than metal cations – close packed oxygen in a lattice (usually FCC) – cations fit into interstitial sites among oxygen ions



Chapter 12 - 6

Factors that Determine Crystal Structure 1. Relative sizes of ions – Formation of stable structures: --maximize the # of oppositely charged ion neighbors.

Adapted from Fig. 3.4, Callister & Rethwisch 3e.

- -

- - +

unstable

- -

- - +

stable

- -

- - +

stable 2. Maintenance of Charge Neutrality : --Net charge in ceramic should be zero. --Reflected in chemical formula:

CaF 2 : Ca 2+ cation

F -

F -

anions +

A m X p m, p values to achieve charge neutrality



Chapter 12 - 7

• Coordination # increases with

Coordination # and Ionic Radii

Adapted from Table 3.3, Callister & Rethwisch 3e.

2

r cation r anion

Coord #

< 0.155

0.155 - 0.225

0.225 - 0.414

0.414 - 0.732

0.732 - 1.0

3

4

6

8

linear

triangular

tetrahedral

octahedral

cubic




ZnS (zinc sulfide)

NaCl (sodium chloride)

CsCl (cesium chloride)

r cation r anion

To form a stable structure, how many anions can surround around a cation?



Chapter 12 - 8

Computation of Minimum Cation-Anion Radius Ratio

• Determine minimum rcation/ranion for an octahedral site (C.N. = 6)

a = 2ranion

2ranion + 2rcation = 2 2ranion

ranion + rcation = 2ranion

rcation = ( 2 −1)ranion

arr 222 cationanion =+

414.012anion

cation =−=rr



Chapter 12 - 9

• On the basis of ionic radii, what crystal structure would you predict for FeO?

• Answer:

550014000770

anion

cation

...

rr

=

=

based on this ratio, -- coord # = 6 because

0.414 < 0.550 < 0.732

-- crystal structure is NaCl Data from Table 3.4, Callister & Rethwisch 3e.

Example: Predicting the Crystal Structure of FeO

Ionic radius (nm) 0.053 0.077 0.069 0.100

0.140 0.181 0.133

Cation

Anion

Al 3+

Fe 2 +

Fe 3+

Ca 2+

O 2-

Cl -

F - Materials Science - Prof. Choi, Hae-Jin


Chapter 12 - 10

Rock Salt Structure Same concepts can be applied to ionic solids in general. Example: NaCl (rock salt) structure

rNa = 0.102 nm

rNa/rCl = 0.564 ∴ cations (Na+) prefer octahedral sites


rCl = 0.181 nm



Chapter 12 - 11

MgO and FeO

O2- rO = 0.140 nm

Mg2+ rMg = 0.072 nm

rMg/rO = 0.514 ∴ cations prefer octahedral sites

So each Mg2+ (or Fe2+) has 6 neighbor oxygen atoms


MgO and FeO also have the NaCl structure



Chapter 12 - 12

AX Crystal Structures

939.0181.0170.0

Cl

Cs ==−

+

r

r


Cesium Chloride structure:

∴ Since 0.732 < 0.939 < 1.0, cubic sites preferred

So each Cs+ has 8 neighbor Cl-

AX–Type Crystal Structures include NaCl, CsCl, and zinc blende



Chapter 12 - 13

AX2 Crystal Structures

• Calcium Fluorite (CaF2) • Cations in cubic sites

• UO2, ThO2, ZrO2, CeO2

• Antifluorite structure – positions of cations and anions reversed


Fluorite structure



Chapter 12 - 14

ABX3 Crystal Structures


• Perovskite structure Ex: complex oxide BaTiO3



Chapter 12 - 15

Density Computations for Ceramics

A

AC )(NV

AAn

C

Σ+Σ′=ρ

Number of formula units/unit cell

Volume of unit cell

Avogadro’s number

= sum of atomic weights of all anions in formula unit

ΣAA

ΣAC = sum of atomic weights of all cations in formula unit



Chapter 12 - 16

Densities of Material Classes ρ metals > ρ ceramics > ρ polymers

Why?

Data from Table B.1, Callister & Rethwisch, 3e.

ρ (g/

cm )

3

Graphite/ Ceramics/ Semicond

Metals/ Alloys

Composites/ fibers Polymers

1

2

2 0

30 B ased on data in Table B1, Callister

*GFRE, CFRE, & AFRE are Glass, Carbon, & Aramid Fiber-Reinforced Epoxy composites (values based on 60% volume fraction of aligned fibers

in an epoxy matrix). 10

3 4 5

0.3 0.4 0.5

Magnesium

Aluminum

Steels

Titanium

Cu,Ni Tin, Zinc

Silver, Mo

Tantalum Gold, W Platinum

G raphite Silicon Glass - soda Concrete

Si nitride Diamond Al oxide

Zirconia

H DPE, PS PP, LDPE PC

PTFE

PET PVC Silicone

Wood

AFRE * CFRE * GFRE* Glass fibers

Carbon fibers A ramid fibers

Metals have... • close-packing (metallic bonding) • often large atomic masses Ceramics have... • less dense packing • often lighter elements Polymers have... • low packing density (often amorphous) • lighter elements (C,H,O) Composites have... • intermediate values

In general



Chapter 12 - 17

Silicate Ceramics Most common elements on earth are Si & O

• SiO2 (silica) polymorphic forms are quartz, crystobalite, & tridymite

• The strong Si-O bonds lead to a high melting temperature (1710ºC) for this material

Si4+

O2-

Adapted from Figs. 3.10-11, Callister & Rethwisch 3e crystobalite



Chapter 12 - 18

• Quartz is crystalline SiO2:

• Basic Unit: Glass is noncrystalline (amorphous) • Fused silica is SiO2 to which no impurities have been added • Other common glasses contain impurity ions such as Na+, Ca2+, Al3+, and B3+

(soda glass) Adapted from Fig. 3.41, Callister & Rethwisch 3e.

Glass Structure

Si0 4 tetrahedron 4-

Si 4+

O 2 -

Si 4+ Na +

O 2 -



Chapter 12 - 19

Polymorphic Forms of Carbon Diamond

– tetrahedral bonding of carbon

• hardest material known • very high thermal

conductivity – large single crystals –

gem stones – small crystals – used to

grind/cut other materials – diamond thin films

• hard surface coatings – used for cutting tools, medical devices, etc.




Chapter 12 - 20

Polymorphic Forms of Carbon (cont) Graphite

– layered structure – parallel hexagonal arrays of carbon atoms

– weak van der Waal’s forces between layers – planes slide easily over one another -- good

lubricant




Chapter 12 - 21

Polymorphic Forms of Carbon (cont) Fullerenes and Nanotubes

• Fullerenes – spherical cluster of 60 carbon atoms, C60

– Like a soccer ball • Carbon nanotubes – sheet of graphite rolled into a tube

– Ends capped with fullerene hemispheres

Adapted from Figs. 3.18 & 3.19, Callister & Rethwisch 3e.



Chapter 12 - 22

Point Defects in Ceramics (i) • Vacancies -- vacancies exist in ceramics for both cations and anions • Interstitials -- interstitials exist for cations -- interstitials are not normally observed for anions because anions are large relative to the interstitial sites

Adapted from Fig. 5.2, Callister & Rethwisch 3e. (Fig. 5.2 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.)

Cation Interstitial

Cation Vacancy

Anion Vacancy


Chapter 12 - 23

Point Defects in Ceramics (ii)

• Frenkel Defect -- a cation vacancy-cation interstitial pair. • Shottky Defect -- a paired set of cation and anion vacancies.

• Equilibrium concentration of defects

Adapted from Fig. 5.3, Callister & Rethwisch 3e. (Fig. 5.3 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.)

Shottky Defect:

Frenkel Defect

/kTQDe−∝


Chapter 12 - 24

Imperfections in Ceramics • Electroneutrality (charge balance) must be maintained when impurities are present • Ex: NaCl Na + Cl - • Substitutional cation impurity

without impurity Ca 2+ impurity with impurity

Ca 2+

Na +

Na + Ca 2+

cation vacancy

• Substitutional anion impurity

without impurity O 2- impurity

O 2-

Cl -

an ion vacancy

Cl -

with impurity


Chapter 12 - 25

Brittle Fracture Surfaces • Intergranular (between grains) 304 S. Steel

(metal) Reprinted w/permission from "Metals Handbook", 9th ed, Fig. 633, p. 650. Copyright 1985, ASM International, Materials Park, OH. (Micrograph by J.R. Keiser and A.R. Olsen, Oak Ridge National Lab.)

Polypropylene (polymer) Reprinted w/ permission from R.W. Hertzberg, "Defor-mation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.35(d), p. 303, John Wiley and Sons, Inc., 1996.

4 mm

• Intragranular (within grains)

Al Oxide (ceramic)

Reprinted w/ permission from "Failure Analysis of Brittle Materials", p. 78.

Copyright 1990, The American Ceramic

Society, Westerville, OH. (Micrograph by R.M.

Gruver and H. Kirchner.)

316 S. Steel (metal)

Reprinted w/ permission from "Metals Handbook", 9th ed, Fig. 650, p. 357.

Copyright 1985, ASM International, Materials

Park, OH. (Micrograph by D.R. Diercks, Argonne

National Lab.)

3 mm

160 mm

1 mm (Orig. source: K. Friedrick, Fracture 1977, Vol. 3, ICF4, Waterloo, CA, 1977, p. 1119.)


Chapter 12 -

Brittle Fracture of Ceramics • Characteristic Fracture

behavior in ceramics – Origin point – Initial region (mirror) is flat

and smooth – After reaches critical

velocity crack branches • mist • hackle

26

Adapted from Figs. 9.14 & 9.15, Callister & Rethwisch 3e.


Chapter 12 - 27

Classification of Ceramics

Glasses Clay products

Refractories Abrasives Cements Advanced ceramics

-optical - composite reinforce - containers/ household

-whiteware - structural

-bricks for high T (furnaces)

-sandpaper - cutting - polishing

-composites - structural

-engine rotors valves bearings

-sensors Adapted from Fig. 13.7 and discussion in Section 13.4-10, Callister & Rethwisch 3e.

Ceramic Materials


Chapter 12 - 28

Ceramics Application: Die Blanks

tensile force

A o A d die

die

• Die blanks: -- Need wear resistant properties!

• Die surface: -- 4 µm polycrystalline diamond particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond gives uniform hardness in all directions to reduce wear.

Adapted from Fig. 14.2 (d), Callister & Rethwisch 3e.

Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.


Chapter 12 - 29

Ceramics Application: Cutting Tools

• Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling

blades oil drill bits

Single crystal diamonds

polycrystalline diamonds in a resin matrix.

Photos courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

• Materials: -- manufactured single crystal or polycrystalline diamonds in a metal or resin matrix.

-- polycrystalline diamonds resharpen by microfracturing along cleavage planes.


Chapter 12 - 30

Refractories • Materials to be used at high temperatures (e.g., in high temperature furnaces). • Consider the Silica (SiO2) - Alumina (Al2O3) system. • Silica refractories - silica rich - small additions of alumina depress melting temperature (phase diagram):

Fig. 10.26, Callister & Rethwisch 3e. (Fig. 10.26 adapted from F.J. Klug and R.H. Doremus, J. Am. Cer. Soc. 70(10), p. 758, 1987.)

Composition (wt% alumina)

T(°C)

1400

1600

1800

2000

2200

20 40 60 80 100 0

alumina +

mullite

mullite + L

mullite Liquid

(L)

mullite + crystobalite

crystobalite + L

alumina + L

3Al2O3-2SiO2


Chapter 12 -

Advanced Ceramics: Materials for Automobile Engines

• Advantages:

– Operate at high temperatures – high efficiencies

– Low frictional losses – Operate without a cooling

system – Lower weights than

current engines

31

• Disadvantages:

– Ceramic materials are brittle

– Difficult to remove internal voids (that weaken structures)

– Ceramic parts are difficult to form and machine

• Potential candidate materials: Si3N4, SiC, & ZrO2 • Possible engine parts: engine block & piston coatings


Chapter 12 -

Advanced Ceramics: Materials for Ceramic Armor

32

Components: -- Outer facing plates -- Backing sheet Properties/Materials: -- Facing plates -- hard and brittle — fracture high-velocity projectile — Al2O3, B4C, SiC, TiB2 -- Backing sheets -- soft and ductile — deform and absorb remaining energy — aluminum, synthetic fiber laminates


Chapter 12 - 33

• Blowing of Glass Bottles:

GLASS FORMING

Adapted from Fig. 14.18, Callister & Rethwisch 3e. (Fig. 14.18 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

Ceramic Fabrication Methods (i)

Gob

Parison mold

Pressing operation

Suspended parison

Finishing mold

Compressed air

• Fiber drawing:

wind up

PARTICULATE FORMING

CEMENTATION

-- glass formed by application of pressure -- mold is steel with graphite lining

• Pressing: plates, cheap glasses


Chapter 12 - 34

Sheet Glass Forming • Sheet forming – continuous casting

– sheets are formed by floating the molten glass on a pool of molten tin



Chapter 12 - 35

• Quartz is crystalline SiO2:

• Basic Unit: Glass is noncrystalline (amorphous) • Fused silica is SiO2 to which no impurities have been added • Other common glasses contain impurity ions such as Na+, Ca2+, Al3+, and B3+

(soda glass) Adapted from Fig. 3.41, Callister & Rethwisch 3e.

Glass Structure

Si0 4 tetrahedron 4-

Si 4+

O 2 -

Si 4+ Na +

O 2 -


Chapter 12 - 36

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

• Glasses: -- do not crystallize -- change in slope in spec. vol. curve at glass transition temperature, Tg -- transparent - no grain boundaries 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)

Tg

Glass (amorphous solid)


Chapter 12 - 37

Glass Properties: Viscosity

• Viscosity, η: -- relates shear stress (τ) and velocity gradient (dv/dy):

η has units of (Pa-s)

dydv /τ

=η

velocity gradient

dv dy

τ

τ

glass dv dy


Chapter 12 - 38

Visc

osity

[Pa-

s]

1 10 2

10 6

10 10

10 14

200 600 1000 1400 1800 T(°C)

Working range: glass-forming carried out

annealing point

Tmelt

strain point

• Viscosity decreases with T

Adapted from Fig. 14.17, Callister & Rethwisch 3e. (Fig. 14.17 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.)

Log Glass Viscosity vs. Temperature

• 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


Chapter 12 - 39

• Annealing: -- removes internal stresses caused by uneven cooling. • Tempering: -- puts surface of glass part into compression -- suppresses growth of cracks from surface scratches. -- sequence:

Heat Treating Glass

at room temp.

tension compression

compression

before cooling

hot

initial cooling

hot cooler

cooler

-- Result: surface crack growth is suppressed.


Chapter 12 - 40

• Mill (grind) and screen constituents: desired particle size • Extrude this mass (e.g., into a brick)

• Dry and fire the formed piece

ram billet

container

container force die holder

die

A o

A d extrusion Adapted from Fig. 14.2 (c), Callister & Rethwisch 3e.

Ceramic Fabrication Methods (iia)

GLASS FORMING

PARTICULATE FORMING

CEMENTATION

Hydroplastic forming:


Chapter 12 - 41

• Mill (grind) and screen constituents: desired particle size

• Slip casting operation

• Dry and fire the cast piece

Ceramic Fabrication Methods (iia)

solid component

Adapted from Fig. 14.22, Callister & Rethwisch 3e. (Fig. 14.22 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

hollow component

pour slip into mold

drain mold

“green ceramic”

pour slip into mold

absorb water into mold “green

ceramic”

GLASS FORMING

PARTICULATE FORMING

CEMENTATION

Slip casting:

• Mix with water and other constituents to form slip


Chapter 12 - 42

Typical Porcelain Composition (50%) 1. Clay (25%) 2. Filler – e.g. quartz (finely ground) (25%) 3. Fluxing agent (Feldspar)

-- aluminosilicates plus K+, Na+, Ca+

-- upon firing - forms low-melting-temp. glass


Chapter 12 - 43

• Clay is inexpensive • When water is added to clay -- water molecules fit in between layered sheets -- reduces degree of van der Waals bonding -- when external forces applied – clay particles free to move past one another – becomes hydroplastic

• Structure of Kaolinite Clay:

Adapted from Fig. 3.14, Callister & Rethwisch 3e. (Fig. 3.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)

Hydroplasticity of Clay

weak van der Waals bonding

charge neutral

charge neutral

Si 4+

Al 3 + - OH

O 2-

Shear

Shear


Chapter 12 - 44

• Drying: as water is removed - interparticle spacings decrease – shrinkage .

Adapted from Fig. 14.23, Callister & Rethwisch 3e. (Fig. 14.23 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

Drying and Firing

Drying too fast causes sample to warp or crack due to non-uniform shrinkage wet body partially dry completely dry

• Firing: -- heat treatment between 900-1400°C -- vitrification: liquid glass forms from clay and flux – flows between SiO2 particles. (Flux lowers melting temperature). Adapted from Fig. 14.24, Callister & Rethwisch 3e.

(Fig. 14.24 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)

Si02 particle (quartz)

glass formed around the particle

mic

rogr

aph

of p

orce

lain

70 µm


Chapter 12 - 45

Powder Pressing: used for both clay and non-clay compositions. • Powder (plus binder) compacted by pressure in a mold -- Uniaxial compression - compacted in single direction -- Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope -- Hot pressing - pressure + heat

Ceramic Fabrication Methods (iib)

GLASS FORMING

PARTICULATE FORMING

CEMENTATION


Chapter 12 - 46

Sintering


Aluminum oxide powder: -- sintered at 1700°C for 6 minutes.

Adapted from Fig. 14.27, Callister & Rethwisch 3e. (Fig. 14.27 is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.)

15 µm

Sintering occurs during firing of a piece that has been powder pressed -- powder particles coalesce and reduction of pore size


Chapter 12 - 47

Tape Casting • Thin sheets of green ceramic cast as flexible tape • Used for integrated circuits and capacitors • Slip = suspended ceramic particles + organic liquid

(contains binders, plasticizers)

Fig. 14.28, Callister & Rethwisch 3e.


Chapter 12 - 48

• Hardening of a paste – paste formed by mixing cement material with water • Formation of rigid structures having varied and complex shapes • Hardening process – hydration (complex chemical reactions involving water and cement particles)

Ceramic Fabrication Methods (iii)

GLASS FORMING

PARTICULATE FORMING

CEMENTATION

• Portland cement – production of: -- mix clay and lime-bearing minerals -- calcine (heat to 1400°C) -- grind into fine powder


chapter 12,13: ceramics - 중앙대학교 시스템 융합설계 연구실...

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