Download - MSE 131 Ceramics Lecture 1 2016 Student
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MSE 131 CeramicsLecture 1
Dr. Benjamin O. Chan
Physics Department
Ateneo de Manila University2016
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Types of Ceramics
Traditional ceramicsAbrasive products, clay products, construction,
glass, refractories, whitewares Industrial/Engineering/Advanced ceramics
Automotive, aerospace, electronics, hightemperature, manufacturing, medical
Fine ceramics Very small grain sizes
Nanoceramics
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Ceramic Bonds
Covalent
Electrons shared betweenatoms
Ionic One atom gives willingly, the other readily takes
Extreme form of covalent bond
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Partially Covalent/Ionic Bonds
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Associated Crystal Structures
Diatomic Structures
Diamond/Zincblende
CsCl
NaCl
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Stability of Anion-Cation
Configurations
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Stable Configurations I
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Determining Critical Size
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Stable Configurations II
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Some Ionic Radii
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Stable Crystal Structures
Things to consider
Difference in electronegativity
Atomic bonding Stoichiometry
r/R ratio
Coordination number
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Example: MgO
EN = 3.44-1.31 = 2.13 (68% ionic)
Ionic Bond between Mg and O
r(Mg2+
) = r = 0.078 nm r(O2-) = R = 0.132 nm
r/R = 0.078/0.132 = 0.591
CN = 6
NaCl structure Diatomic FCC with
octahedral sites filled bycations
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Example: CsI
EN = 2.66 0.79 = 1.87
58% ionic
r/R = 0.167/0.220 = 0.76,CN = 8
CsCl structure
Diatomic simple cubicstructure with the bodycenter occupied by acation
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Example: GaAs
EN = 2.18 1.81 = 0.37, 3% ionic
metallic or covalent
Valence = (3+5)/2 = 4 > 3Covalent bond
CN = 8 Valence = 4
Zincblende structure
Diatomic FCC with thecation occupying
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What happens if the cationand anion are of the same
size?
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Atomic Packing Factor: NaCl
Fractional volume occupied by atoms
r(Na+) = r = 0.098 nm
r(Cl
-
) = R = 0.181 nm
APF = 66.3%
3
33
3
33
)(3
2
8
)3
43
4(4
Rr
Rr
Rr
Rr
APF
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Density Calculation: CsCl
r(Cs+) = 0.167 nm
r(Cl-) = 0.181 nm
AtWt(Cs+) = 132.9 g/mol
At Wt(Cl-) = 35.45 g/mol M = (132.9g/6.023x1023) + (35.45/ 6.023x1023)
= 2.8 x 10-22g
V = ao3 = (2(0.167nm+0.181nm)/31/2)3
= 6.49x 10-23
cm3
= M/V = 2.8x10-22g/ 6.49x 10-23cm3
= 4.31 g/cm3
*experimental density is 3.99 g/cm3
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Three or more atoms in the basis
Fluorite (CaF2)
Perovskite (BaTiO3)
Crystobalite (SiO2)
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Silicates
Main components are Si and O
Consider arrangement of SiO44-
tetrahedron
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Silica
Every corner O in each tetrahedron is shared
by adjacent tetrahedra
Polymorphic forms: quartz, crystobalite,tridymite
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Silicates
Corner atom shared by 1, 2 or 3 tetrahedra
Cations (Ca2+, Mg2+,Al3+) compensate
negative tetrahedral charge and bond themtogether
a) Forsterite (Mg2SiO4)
b) Akermanite
(Ca2MgSi2O7)
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Layered Silicates
Sheet forms on sharing 3 O ions (Si2O5)2-
Second sheet neutralizes sheet
Kaolinite clayAl2(Si2O5) (OH)4
Talc
Mg3(Si2O5) 2(OH)2
Mica
KAl3Si3O10(OH)2
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Carbon
Diamond
Graphite
Fullerenes
CNT
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Homework
Compare the densities of diamond,
graphite, fullerene and carbon
nanotubes. Make observations orcomments on the values.
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Piezo-ceramics
Induced polarization upon
application of stress
Inverse effect: application of
electric field generates stress
Curie temperature
Transformation from cubic to
orthorhombic Orthorhombic structure is
susceptible to polarization
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Piezo-ceramics
Poling generates hysteresis
and remanent polarization
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Piezo-ceramics
Hard
Can be exposed to repetitive high electrical
and mechanical stresses Ideal for high-power and ignition applications
Soft
Relatively easy polarization
Suitable for sensing applications, receivers,
actuators and low power transducers
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More Complex Structures
More than one
compound
YBCOsuperconductor
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Non-crystalline Structures
GlassAmorphous structure
Fused/vitreous silica Network formers
B2O3 and GeO2
Network modifiers Na2O, CaO
Intermediates
TiO2, Al2O3
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Determining Crystal Structure
Indirect method
Diffraction (probe beam must have
wavelength < lattice spacing)Direct method
STM
AFMCan only see surface and immediate layers
below it
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Determining Composition
Spectroscopy
UV-VIS
IR X-ray
Mass spectroscopy
Nuclear Magnetic Resonance
Rutherford Backscattering
Neutron Activation Analysis
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Crystal Defects
Point: 0-D
Line: 1-D
Area: 2-D
Volume: 3-D
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Point Defects
Vacancies
Missing host atom
Self-interstitialsDisplaced (misplaced)
host atom
Impurities
Foreign atoms Interstitial
Substitutional
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Ionic Crystal Point Defects
Charge neutrality maintained
Frenkel Defect: vacancy-interstitial pair
Schottky Defect: vacancy pair
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Impurities
Intrinsic Starting material (from growth)
Extrinsic From material processing
From device fabrication
Intentional
To attain desired property Included during growth or processing
Doping
Charge neutrality is maintained
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Location of Impurities Interstitial
Occupying interstitial sites (in between host atoms)
Substitutional Occupying vacancy sites (replacing host atoms in the lattice)
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Interstitial or Substitutional?
Hume-Rothery rules Size difference not greater than 15%
EN comparable
Similar valence ( 1, 2)* same crystal structure
for complete solubility
can be ignored for dilute solutions
Satisfy first three conditions, impurity atomwill occupy a substitutional site
Otherwise, interstitial site Size must be comparable to interstitial site