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Definition of ceramicsDefinition of ceramics

from the Greek word keramikos burntstuff; desirable properties are normally

achieved through a high-temperature heattreatment process called firing orsintering

Source: http://www.alphafiredarts.com/claystudio.html

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Traditional CeramicsTraditional Ceramics

Source: http://203.148.253.29/annaart/

Source:http://www.aqualon.ashland.com/industries/Specialties_S

olutions/Applications/Ceramics/Traditional_Ceramics_and

_Glazes.aspx

Source:

http://www.indiamart.com/topma

rble-granite/building-hardware.html

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Definition of ceramicsDefinition of ceramics

solid compounds that are formed by theapplication ofheat, and sometimes heat andpressure, comprising:

a. at least one nonmetal or a nonmetallicelemental solid (NMES) and

b. One or more of a metal/s, nonmetal or

NMES/s

Ex. SiO2 (silica), TiO2, SiC, BaTiO3, YBa2Cu3O7,Ti3SiC2

*Oxides, nitrides, borides, carbides and silicides

of all metals and NMES are ceramics. Silicates

are also, by definition, ceramics.

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Engineering/Engineered CeramicsEngineering/Engineered Ceramics

Source:

http://www.newworldencyclopedia.or

g/entry/Image:Shuttle_STS-45.jpg

Source:

http://www.avure.com/iso/applic

ations/advanced-ceramics.asp

Source: http://www.hannongroup.com/

Source: http://www.amazon.com/Ceramic-

Hex-Bolt-Length-Pack/dp/B000FN1DVW

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General properties of ceramics:General properties of ceramics:

1. generally stiff and strong (comparable tometals)

2. very hard3. extremely brittle and susceptible to fracture

4. insulative to heat and electricity

5. more resistant to high temperatures andharsh environments (compared to metals

and polymers)6. may be transparent, translucent or opaque

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RoomRoom--temperature elastic modulus comparisontemperature elastic modulus comparison

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RoomRoom--temperature tensile strength comparisontemperature tensile strength comparison

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RoomRoom--temperature electrical conductivity comparisontemperature electrical conductivity comparison

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Optical propertyOptical property

Disk specimens of aluminum oxide (Al2O3)

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Crystalline vs. amorphous solidsCrystalline vs. amorphous solids

Crystalline solid

solids that exhibit long-range order

Amorphous, glassy or noncrystalline solid solids which lack periodicity

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Basic terminologiesBasic terminologies

Single crystal

solids in which the periodic arrangement of atomsis perfect and extends throughout the entirety of thespecimen without interruption

Polycrystalline solid

composed of a collection of many single crystals,termed grains, separated from one another byareas of disorder known as grain boundaries

Microstructure

describes the shape and size of the grains,together with the presence of porosity, second

phases, etc., and their distribution

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Bonding in ceramicsBonding in ceramics

atomic bonding ranges from purely ionic to totallycovalent (degree depends on theelectronegativities, X of the atoms)

( )( ) 10025.0exp1% 2 = BA XXcharacterionic

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Ceramic crystal structuresCeramic crystal structures

for predominantly ionic materials, crystalstructure is composed of metallic cationsand nonmetallic anions

characteristics of the component ions whichinfluence the crystal structure:

a. magnitude of the electrical charge (crystalmust be electrically neutral)

b. relative sizes of cations, rC and anions, rA

stable ceramic structures: anionssurrounding a cation are in contact with thatcation

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Ceramic crystal structuresCeramic crystal structures

for a specific coordination number, there is acritical rC/rA ratio for which cation-anion contact isestablished

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Most common coordination numbers for ceramics

are 4, 6 or 8.

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Sample problemSample problem

Show that the minimum cation-to-anion radiusratio for the coordination number 3 is 0.155

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AXAX--Type crystal structuresType crystal structures

equal number of cations and anions

Rock salt structure

- cation and anion CN is 6

- thought of as two

interpenetrating FCC lattices- ex. NaCl, MgO, MnS, LiF,and FeO

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AXAX--Type crystal structuresType crystal structures

Cesium Chloride structure

- cation and anion CN is 8- anions: cube corners;

cation: cube center

- ex. CsCl

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AXAX--Type crystal structuresType crystal structures

Zinc blende structure

- cation and anion CN is 4(all ions are tetrahedrallycoordinated)

- bonding is often highlycovalent

- ex. ZnS, ZnTe, SiC

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AAmmXXpp --Type crystal structuresType crystal structures

when cation and anion

charges are not the same AmXp, where m and/or p

1 CN = 8 ex. CaF2, UO2, PuO2, and

ThO2

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AAmmBBnnXXpp --Type crystal structuresType crystal structures

for compounds with two

types of cations

ex. BaTiO3 (perovskitestructure)

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CloseClose--packed anion structurepacked anion structure

Ceramic crystal structures depend on:

stacking of the close-packed anion layers

manner in which the interstitial sites are filled withcations

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Sample problemSample problem

On the basis of ionic radii, what crystalstructure would you predict for FeO?

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Sample problemSample problem

On the basis of crystal structure, compute thetheoretical density for sodium chloride.