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Ceramic Their Properties and Material Behavior. Engr 2110 Dr. R. Lindeke. Taxonomy of Ceramics. Glasses. Clay . Refractories. Abrasives. Cements. Advanced . products. ceramics. -bricks for . -optical . -whiteware . -sandpaper . -composites . engine . high T . -. composite . -.

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Taxonomy of ceramics l.jpg
Taxonomy of Ceramics

Glasses

Clay

Refractories

Abrasives

Cements

Advanced

products

ceramics

-bricks for

-optical

-whiteware

-sandpaper

-composites

engine

high T

-

composite

-

bricks

-

cutting

-

structural

-

rotors

(furnaces)

reinforce

-

polishing

-

valves

-

containers/

-

bearings

Adapted from Fig. 13.1 and discussion in Section 13.2-6, Callister 7e.

household

-sensors

• 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.


Ceramic bonding l.jpg
Ceramic Bonding

CaF2: large

SiC: small

• Bonding:

-- Mostly ionic, some covalent.

-- % ionic character increases with difference in

electronegativity (remember!?!).

• Large vs small ionic bond character:

Adapted from Fig. 2.7, Callister 7e. (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.


Ceramic crystal structures l.jpg
Ceramic Crystal Structures

Oxide structures

  • oxygen anions much larger than metal cations

  • close packed oxygen in a lattice (usually FCC)

  • cations in the holes of the oxygen lattice

  • The same ideas apply to all “ceramics”

  • Principles of Ceramic Architecture:

    • Size relationships Cation to Anion

    • Electrical Neutrality of the overall structure

    • Crystallographic Arrangements

    • Stoichiometry Must Match


  • Silica glass l.jpg
    Silica Glass

    • A “Dense form” of amorphous silica

      • Charge imbalance corrected with “counter cations” such as Na+

      • Borosilicate glass is the pyrex glass used in labs

        • better temperature stability & less brittle than sodium glass


    Slide6 l.jpg

    Table 13.1

    GLASSES – transparent and easily shaped

    Noncrystalline Silicates + oxides (CaO, Na2O, K2O, Al2O3)

    E.g. Soda lime glass = 70wt% SiO2 + 30% [Na2O (soda) and CaO(lime)


    Glass properties l.jpg
    GLASS PROPERTIES

    • Viscosity:

    --relates shear stress &

    velocity gradient:

    --has units of (Pa-s)

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

    • Crystalline materials:

    --crystallize at melting temp, Tm

    --have abrupt change in spec.

    vol. at Tm

    • Glasses:

    --do not crystallize

    --spec. vol. varies smoothly with T

    --Glass transition temp, Tg

    Adapted from Fig. 13.5, Callister, 6e.

    9


    Glass viscosity vs t and impurities l.jpg
    GLASS VISCOSITY VS T AND IMPURITIES

    from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.

    • Viscosity decreases with T increase

    • Impurities lower Tdeform

    10


    Slide9 l.jpg

    Important Temperatures

    • Melting point = viscosity of 10 Pa.s

    • Working point= viscosity of 1000 Pa.s

    • Softening point= viscosity of 4x107Pa.s

    • Temperature above which glass cannot

    • be handled without altering dimensions)

    • Annealing point= viscosity of 1012 Pa.s.

    • Strain point = viscosity of 3x1013Pa.s

    • Fracture occurs before deformation

    • Viscosity decreases with T

    • Impurities lower Tdeform


    Silicates l.jpg
    Silicates

    • Combine SiO44- tetrahedra by having them share corners, edges, or faces

    • Cations such as Ca2+, Mg2+, & Al3+ act to neutralize & provide ionic bonding

    Mg2SiO4

    Ca2MgSi2O7


    Layered silicates l.jpg

    =

    Layered Silicates

    • Layered silicates (clay silicates)

      • SiO4 tetrahedra connected together to form 2-D plane

    • (Si2O5)2-

    • So need cations to balance charge


    Layered silicates12 l.jpg
    Layered Silicates

    • Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)42+ layer

    Adapted from Fig. 12.14, Callister 7e.

    Note: these sheets loosely bound by van der Waal’s forces


    Layered silicates13 l.jpg
    Layered Silicates

    • Can change the counterions

      • this changes layer spacing

      • the layers also allow absorption of water

    • Micas: KAl3Si3O10(OH)2

    • Bentonite

      • used to seal wells

      • packaged dry

      • swells 2-3 fold in H2O

      • pump in to seal up well so no polluted ground water seeps in to contaminate the water supply.

      • Used in bonding Foundry Sands and Taconite pellets


    Carbon forms l.jpg
    Carbon Forms

    • Carbon black – amorphous – surface area ca. 1000 m2/g

    • Diamond

      • tetrahedral carbon

        • hard – no good slip planes

        • brittle – can cleave (cut) it

      • large diamonds – jewelry

      • small diamonds

        • often man made - used for cutting tools and polishing

      • diamond films

        • hard surface coat – cutting tools, medical devices, etc.


    Carbon forms graphite l.jpg
    Carbon Forms - Graphite

    • layer structure – aromatic layers

      • weak van der Waal’s forces between layers

      • planes slide easily, good lubricant


    Carbon forms fullerenes and nanotubes l.jpg
    Carbon Forms – Fullerenes and Nanotubes

    • Fullerenes or carbon nanotubes

      • wrap the graphite sheet by curving into ball or tube

      • Buckminister fullerenes

        • Like a soccer ball C60 - also C70 + others

    Adapted from Figs. 12.18 & 12.19, Callister 7e.


    Defects in ceramic structures l.jpg
    Defects in Ceramic Structures

    Shottky

    Defect:

    Frenkel

    Defect

    • Frenkel Defect

    --a cation is out of place.

    • Shottky Defect

    --a paired set of cation and anion vacancies.

    Adapted from Fig. 12.21, Callister 7e. (Fig. 12.21 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.)

    • Equilibrium concentration of defects


    Mechanical properties l.jpg
    Mechanical Properties

    We know that ceramics are more brittle than metals. Why?

    • Consider method of deformation

      • slippage along slip planes

        • in ionic solids this slippage is very difficult

        • too much energy needed to move one anion past another anion (like charges repel)


    Measuring elastic modulus l.jpg
    Measuring Elastic Modulus

    F

    cross section

    L/2

    L/2

    d

    R

    b

    d = midpoint

    rect.

    circ.

    deflection

    • Determine elastic modulus according to:

    F

    3

    3

    F

    L

    F

    L

    =

    =

    E

    x

    3

    4

    d

    d

    p

    F

    4

    bd

    12

    R

    slope =

    rect.

    circ.

    d

    cross

    cross

    d

    section

    section

    linear-elastic behavior

    • Room T behavior is usually elastic, with brittle failure.

    • 3-Point Bend Testing often used.

    --tensile tests are difficult for brittle materials!

    Adapted from Fig. 12.32, Callister 7e.


    Measuring strength l.jpg
    Measuring Strength

    F

    cross section

    L/2

    L/2

    d

    R

    b

    location of max tension

    d = midpoint

    rect.

    circ.

    deflection

    • Typ. values:

    • Flexural strength:

    s

    Material

    (MPa) E(GPa)

    fs

    1.5Ff L

    Ff L

    s

    =

    =

    Si nitride

    Si carbide

    Al oxide

    glass (soda)

    250-1000

    100-820

    275-700

    69

    304

    345

    393

    69

    fs

    bd2

    pR3

    rect.

    F

    x

    Ff

    Data from Table 12.5, Callister 7e.

    d

    d

    fs

    • 3-point bend test to measure room T strength.

    Adapted from Fig. 12.32, Callister 7e.


    Mechanical issues l.jpg
    Mechanical Issues:

    • Properties are significantly dependent on processing – and as it relates to the level of Porosity:

      • E = E0(1-1.9P+0.9P2) – P is fraction porosity

      • fs = 0e-nP -- 0 & n are empirical values

  • Because the very unpredictable nature of ceramic defects, we do not simply add a factor of safety for tensile loading

    • We may add compressive surface loads

    • We often choose to avoid tensile loading at all – most ceramic loading of any significance is compressive (consider buildings, dams, brigdes and roads!)


  • Application refractories l.jpg
    Application: Refractories

    2200

    3Al2O3-2SiO2

    T(°C)

    mullite

    2000

    Liquid

    alumina + L

    (L)

    1800

    mullite

    alumina

    crystobalite

    + L

    +

    + L

    1600

    mullite

    mullite

    +

    crystobalite

    1400

    0

    20

    40

    60

    80

    100

    Composition (wt% alumina)

    • Need a material to use in high temperature furnaces.

    • Consider the Silica (SiO2) - Alumina (Al2O3) system.

    • Phase diagram shows:

    mullite, alumina, and crystobalite as candidate refractories.

    Adapted from Fig. 12.27, Callister 7e. (Fig. 12.27 is adapted from F.J. Klug and R.H. Doremus, "Alumina Silica Phase Diagram in the Mullite Region", J. American Ceramic Society70(10), p. 758, 1987.)


    Application die blanks l.jpg
    Application: Die Blanks

    die

    A

    d

    tensile

    A

    o

    force

    die

    • Die blanks:

    -- Need wear resistant properties!

    Adapted from Fig. 11.8 (d), Callister 7e.

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

    • Die surface:

    -- 4 mm polycrystalline diamond

    particles that are sintered onto a

    cemented tungsten carbide

    substrate.

    -- polycrystalline diamond helps control

    fracture and gives uniform hardness

    in all directions.

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


    Application cutting tools l.jpg
    Application: Cutting Tools

    • Tools:

    -- for grinding glass, tungsten,

    carbide, ceramics

    -- for cutting Si wafers

    -- for oil drilling

    • Solutions:

    blades

    oil drill bits

    -- manufactured single crystal or polycrystalline diamonds

    in a metal or resin matrix.

    coated single

    crystal diamonds

    -- optional coatings (e.g., Ti to help

    diamonds bond to a Co matrix

    via alloying)

    polycrystalline

    diamonds in a resin

    matrix.

    -- polycrystalline diamonds

    resharpen by microfracturing

    along crystalline planes.

    Photos courtesy Martin Deakins,

    GE Superabrasives, Worthington,

    OH. Used with permission.


    Application sensors l.jpg
    Application: Sensors

    2+

    Ca

    • Approach:

    Add Ca impurity to ZrO2:

    -- increases O2- vacancies

    -- increases O2- diffusion rate

    2+

    A

    Ca

    impurity

    4+

    removes a

    Zr

    and a

    2

    -

    O

    ion.

    • Operation:

    -- voltage difference

    produced when

    O2- ions diffuse

    from the external

    surface of the sensor

    to the reference gas.

    sensor

    gas with an

    reference

    unknown, higher

    gas at fixed

    2-

    O

    oxygen content

    oxygen content

    diffusion

    -

    +

    voltage difference produced!

    • Example: Oxygen sensor ZrO2

    • Principle: Make diffusion of ions

    fast for rapid response.


    Alternative energy titania nano tubes l.jpg
    Alternative Energy – Titania Nano-Tubes

    "This is an amazing material architecture for water photolysis," says Craig Grimes, professor of electrical engineering and materials science and engineering. Referring to some recent finds of his research group (G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, C. A. Grimes, Enhanced Photocleavage of Water Using Titania Nanotube-Arrays, Nano Letters, vol. 5, pp. 191-195.2005 ), "Basically we are talking about taking sunlight and putting water on top of this material, and the sunlight turns the water into hydrogen and oxygen. With the highly-ordered titanium nanotube arrays, under UV illumination you have a photoconversion efficiency of 13.1%. Which means, in a nutshell, you get a lot of hydrogen out of the system per photon you put in. If we could successfully shift its bandgap into the visible spectrum we would have a commercially practical means of generating hydrogen by solar energy.


    Ceramic fabrication methods i l.jpg
    Ceramic Fabrication Methods-I

    Pressing

    Gob

    operation

    Parison

    mold

    • Fiber drawing:

    Compressed

    • Blowing:

    air

    suspended

    Parison

    Finishing

    mold

    wind up

    PARTICULATEFORMING

    CEMENTATION

    GLASS

    FORMING

    • Pressing:

    plates, dishes, cheap glasses

    --mold is steel with graphite lining

    Adapted from Fig. 13.8, Callister, 7e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)


    Sheet glass forming l.jpg
    Sheet Glass Forming

    • Sheet forming – continuous draw

      • originally sheet glass was made by “floating” glass on a pool of mercury – or tin

    Adapted from Fig. 13.9, Callister 7e.


    Modern plate sheet glass making l.jpg
    Modern Plate/Sheet Glass making:

    Image from Prof. JS Colton, Ga. Institute of Technology


    Heat treating glass l.jpg
    Heat Treating Glass

    before cooling

    surface cooling

    further cooled

    compression

    cooler

    hot

    hot

    tension

    compression

    cooler

    --Result: surface crack growth is suppressed.

    • Annealing:

    --removes internal stress caused by uneven cooling.

    • Tempering:

    --puts surface of glass part into compression

    --suppresses growth of cracks from surface scratches.

    --sequence:


    Ceramic fabrication methods iia l.jpg
    Ceramic Fabrication Methods-IIA

    GLASSFORMING

    PARTICULATE

    FORMING

    CEMENTATION

    Adapted from Fig. 11.8 (c), Callister 7e.

    --Hydroplastic forming:

    extrude the slip (e.g., into a pipe)

    --Slip casting:

    drain

    pour slip

    pour slip

    “green

    absorb water

    mold

    Adapted from Fig. 13.12, Callister 7e.

    (Fig. 13.12 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

    into mold

    A

    into mold

    into mold

    ceramic”

    o

    “green

    container

    die holder

    ceramic”

    force

    ram

    A

    billet

    extrusion

    d

    die

    container

    solid component

    hollow component

    • Milling and screening: desired particle size

    • Mixing particles & water: produces a "slip"

    • Form a "green" component

    • Dry and fire the component


    Clay composition l.jpg
    Clay Composition

    A mixture of components used

    (50%) 1. Clay

    (25%) 2. Filler – e.g. quartz (finely ground)

    (25%) 3. Fluxing agent (Feldspar)

    binds it together

    aluminosilicates + K+, Na+, Ca+


    Features of a slip l.jpg
    Features of a Slip

    Shear

    charge

    neutral

    weak van

    der Waals

    bonding

    4+

    charge

    Si

    3

    +

    neutral

    Al

    -

    OH

    2-

    O

    Shear

    • Clay is inexpensive

    • Adding water to clay

    -- allows material to shear easily

    along weak van der Waals bonds

    -- enables extrusion

    -- enables slip casting

    • Structure of

    Kaolinite Clay:

    Adapted from Fig. 12.14, Callister 7e.

    (Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)


    Drying and firing l.jpg
    Drying and Firing

    wet slip

    partially dry

    “green” ceramic

    • Firing:

    --T raised to (900-1400°C)

    --vitrification: liquid glass forms from clay and flows between

    SiO2 particles. Flux melts at lower T.

    Adapted from Fig. 13.14, Callister 7e.

    (Fig. 13.14 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)

    Si02 particle

    (quartz)

    micrograph of

    glass formed

    porcelain

    around

    the particle

    70mm

    • Drying: layer size and spacing decrease.

    Adapted from Fig. 13.13, Callister 7e.

    (Fig. 13.13 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

    Drying too fast causes sample to warp or crack due to non-uniform shrinkage


    Ceramic fabrication methods iib l.jpg
    Ceramic Fabrication Methods-IIB

    GLASSFORMING

    PARTICULATE

    FORMING

    CEMENTATION

    15m

    Sintering: useful for both clay and non-clay compositions.

    • Procedure:

    -- produce ceramic and/or glass particles by grinding

    -- place particles in mold

    -- press at elevated T to reduce pore size.

    • Aluminum oxide powder:

    -- sintered at 1700°C

    for 6 minutes.

    Adapted from Fig. 13.17, Callister 7e.

    (Fig. 13.17 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.)


    Powder pressing l.jpg
    Powder Pressing

    Sintering - powder touches - forms neck & gradually neck thickens

    • add processing aids to help form neck

    • little or no plastic deformation

    • Uniaxial compression - compacted in single direction

    • Isostatic(hydrostatic) compression - pressure applied by fluid - powder in rubber envelope

    • Hot pressing - pressure + heat

    Adapted from Fig. 13.16, Callister 7e.


    Tape casting l.jpg
    Tape Casting

    • thin sheets of green ceramic cast as flexible tape

    • used for integrated circuits and capacitors

    • cast from liquid slip (ceramic + organic solvent)

    Adapted from Fig. 13.18, Callister 7e.


    Ceramic fabrication methods iii l.jpg
    Ceramic Fabrication Methods-III

    GLASSFORMING

    PARTICULATE

    FORMING

    CEMENTATION

    • Produced in extremely large quantities.

    • Portland cement:

    -- mix clay and lime bearing materials

    -- calcinate (heat to 1400°C)

    -- primary constituents:

    tri-calcium silicate

    di-calcium silicate

    • Adding water

    -- produces a paste which hardens

    -- hardening occurs due to hydration (chemical reactions

    with the water).

    • Forming: done usually minutes after hydration begins.


    Applications advanced ceramics l.jpg
    Applications: Advanced Ceramics

    • Disadvantages:

      • Brittle

      • Too easy to have voids- weaken the engine

      • Difficult to machine

    Heat Engines

    • Advantages:

      • Run at higher temperature

      • Excellent wear & corrosion resistance

      • Low frictional losses

      • Ability to operate without a cooling system

      • Low density

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

      • Ex: Si3N4, SiC, & ZrO2


    Applications advanced ceramics40 l.jpg
    Applications: Advanced Ceramics

    • Ceramic Armor

      • Al2O3, B4C, SiC & TiB2

      • Extremely hard materials

        • shatter the incoming projectile

        • energy absorbent material underneath


    Applications advanced ceramics41 l.jpg
    Applications: Advanced Ceramics

    Electronic Packaging

    • Chosen to securely hold microelectronics & provide heat transfer

    • Must match the thermal expansion coefficient of the microelectronic chip & the electronic packaging material. Additional requirements include:

      • good heat transfer coefficient

      • poor electrical conductivity

    • Materials currently used include:

      • Boron nitride (BN)

      • Silicon Carbide (SiC)

      • Aluminum nitride (AlN)

        • thermal conductivity 10x that for Alumina

        • good expansion match with Si


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