1. No category

4/25/2013
LECTURE #24
Chapters 13 & 14
Structural Materials – Ceramics
Learning
g Objectives:
j
• Role of ceramics and glasses in society
• What are the characteristic properties of ceramics
• Three primary classes:
1) Glasses
2) Crystalline ceramics
3) Glass ceramics
• What are the similarities & differences, what are some
typical applications/examples of each
Relevant Reading for this Lecture...
• Pages 566-577; 613-626
IA
1
H
3
Li
11
Na
19
K
37
Rb
55
Cs
87
Fr
II A
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
CERAMICS
ceramic derives from the Greek roots for
"burnt stuff" — in reference to the hardening
of clays upon high-temperature heat-treatment
27
Co
45
Rh
77
Ir
28
Ni
46
Pd
78
Pt
IB
29
Cu
47
Ag
79
Au
II B
30
Zn
48
Cd
80
Hg
III A
5
B
13
Al
31
Ga
49
In
81
Tl
64
Gd
96
Cm
65
Tb
97
Bk
66
Dy
98
Cf
67
Ho
99
Es
68
Er
100
Fm
VIII B
III B
21
Sc
39
Y
57
La
89
Ac
IV B V B
22
23
Ti
V
40
41
Zr Nb
72
73
Hf Ta
104 105
Rf Db
VI B VII B
24
25
26
Cr Mn Fe
42
43
44
Mo Tc Ru
74
75
76
W Re Os
106
Sg
58
Ce
90
Th
59
Pr
91
Pa
61
Pm
93
Np
Adapted from
Fig. 1.7,
Shackelford 7e.
60
Nd
92
U
62
Sm
94
Pu
63
Eu
95
Am
IV A
6
C
14
Si
32
Ge
50
Sn
82
Pb
VA
7
N
15
P
33
As
51
Sb
83
Bi
VI A VII A
8
9
O
F
16
17
S
Cl
34
35
Se
Br
52
53
Te
I
84
85
Po At
69
Tm
101
Md
70
Yb
102
No
71
Lu
103
Lw
Metal + non-metal  CERAMIC
O
2
He
10
Ne
18
Ar
36
Kr
54
Xe
86
Rn
CERAMIC = metal + non-metal
(hi. density) (low density)
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Classification of Ceramic Materials
• Glasses:
Primarily silica (SiO2) but non-crystalline!
glassware, lenses, fiberglass, windows, borosilicate
glass (Pyrex),
(
) etc.
• Glass-ceramics:
Glasses that have been transformed from a noncrystalline state into a crystalline state through high
temperature heat treatment. (30-90% crystallinity)
Pyroceram Corning Ware,
Pyroceram,
Ware range tops
tops.
• Crystalline ceramics:
Clay, clay products, pottery, china, plumbing fixtures,
refractory ceramics
Glass-ceramics
Glasses
Crystalline ceramics
(all the rest)
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General Properties of Ceramic Materials
• High strength
• Low ductility, catastrophic brittle failure
• Low Thermal & Electrical Conductivity
Stress
tress–
–strain curves for dense,
polycrystalline Al2O3.
Why are ceramics so much stronger in compression compared to tension?
Tension
Compression
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Glasses:
Two prime assets are optical transparency &ease of fabrication

A
Amorphous
h
structure

Fused silica, vitreous silica > 99.5% SiO2

Soda lime glass – silica with soda ash (Na2CO3) and limestone (CaCO3)
Containers (least expansive, easy to work, poor thermal shock resistance)

Optical Flint, (Lead silicate glass, Lead crystal) – used for high degree of
brilliance

Borosilicate Glasses – Pyrex
Glasses are typically non-crystalline!
Vitrification = cooling and remaining
amorphous. Function of:
(a) Viscosity
(b) heat of fusion
(c) mixed bonding
(d) hydrogen bonding
(e) cooling rate (critical)
General properties
Hard and brittle
Chemical resistance
High electrical resistivity
Good spectral transmission
properties
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Crystalline versus Amorphous
Crystalline SiO2 (quartz)
Amorphous SiO2 (glass, fused silica,
vitreous silica)
4 tetrahedra
SiO4 4t t h d are the
th basic
b i units
it for
f eachh
The addition of “modifiers” to SiO2 such as, CaO,
Na2O, B2O3, etc., affects properties, e.g., melting
point, viscosity, thermal shock resistance.
Borosilicate glass (Pyrex) is an example.
Borosilicate Glasses (Pyrex)
• BO33- triangular polyhedra mixed with
SiO44- tetrahedra in a glass forming
network (5 wt.% Na2O provides good
formability)
Ch i l andd cooking
ki ware (introduced
(i t d d
• Chemical
by Corning in 1915)
• High mechanical strength and high
thermal resistance
ts = ET → T = f /E
Thermal Stress
Failure Stress
10.2x106
Esoda lime silica =
psi; Eborosilicate = 9.1x106 psi
but soda lime silica=9x10-6C-1 ; borosilicate=3x10-6C-1
3X difference in 
If boron content is not correct, the thermal resistance
properties change and can be catastrophic (structure
controls properties)
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Fractography Patterns in Glasses (ceramics)
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Example problem
Common soda-lime-silica glass is made by melting together Na2CO3 ,
CaCO3, and SiO2. the carbonates break down, liberating CO2 gas bubbles that help to mix the
molten glass. For 1,000 kg of container glass (15 wt% Na2O, 10 wt% CaO, 75 wt% SiO2),
what is the raw material batch formula (weight percent of Na2CO3, CaCO3 and SiO2)?
Solution:
1,000 kg of glass consists of 150 kg of Na2O, 100 kg of CaO, and 750 kg of
SiO2.
Using data from the periodic table,
mol wt Na2O = 2(22.99)+16.00 =61.98 amu
mol wt Na2CO3 = 2(22.99)+12.00+3(16.00) =105.98 amu
mol wt CaO = 40.08 + 16.00 =56.08 amu
mol wt CaCO3 = 40.08 +12.00+3(16.00) =100.08 amu
Na2CO3 required = 150 kg x 105.98/61.98
105 98/61 98 = 256 kg
CaCO3 required = 100 kg x 100.08/56.08 = 178 kg
SiO2 required = 750 kg
The batch formula is
(256 kg)/(256+178+750)kg x 100 = 21.6 wt % Na2CO3
(178 kg)/(256+178+750)kg x 100 = 15.0 wt % CaCO3
(750 kg)/(256+178+750)kg x 100 = 63.3 wt % SiO2
Glass-Ceramics: Have some degree of crystallinity, high
mechanical strength, low coefficient of thermal expansion (resistant to
thermal shock), tolerance for high temperatures, ease of fabrication
 Pyroceram, Corning Ware
Most glass-ceramics have 30-90% crystallinity
 fast cooling
rates produce
amorphous glass
slower cooling
rates
t produce
d
a
crystalline glass.
long, acicular particles yield
material with unusual strength
and toughness
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Crystalline Ceramics
Clay Products: Inexpensive, found in great abundance, easy to
form into final shapes
 Pottery, china, plumbing fixtures
Refractories: Can withstand high temperatures without melting or
decomposing, inert and unreactive, extremely low thermal conductivity
 Fireclay
 Silica refractories (adicic)
 MgO refractories (basic)
 Special refractories
Crystalline ceramic - Silicon Carbide (SiC)
• Exists in different polymorphs
• ZrB2-SiC offer elevated structural
properties with improved oxidation
• Abrasive (wear resistant)
• Ceramic plates for bullet proof
vests – what does that mean in terms
of properties?
• Semiconductor pproperties
p
((light
g
emitting diode)
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Silica (SiO2)
• Exhibits different polymorphs
(cristobalite, silica, quartz, etc.)
• Abundant
•Readilyy forms on Si wafers – insulator
for semiconductor devices
• Optical fibers: must be extremely high
purity,
it even traces
t
off contaminants
t i t
produce defects that absorb or scatter light
Space Shuttle Tiles –
Silica has low thermal conductivity
100m
Fig. 23.18 Callister
• Glassware
• Protection against temperatures up to
1260 °C.
• NASA estimates its original
acquisition cost was $1,000 per tile
• Aerobraking tiles are produced
from amorphous silica fibers
which are pressed and sintered,
with the resulting tile having as
much as 93% porosity (i.e., very
lightweight) and low thermal
expansion, low thermal
conductivity and good thermal
shock properties.
http://www.enotes.com/w/images/thumb/2/22/Space_Shuttle_(HRSI_tile)
.png/500px-Space_Shuttle_(HRSI_tile).png
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Many crystallographic forms of
SiO2 are stable as they are heated
f
from
room temperature to melting
li
temperature. Each form represents
a different way to connect adjacent
tetrahedra.
Heating SiO2 through 573°C (or other transitions) can cause catastrophic
structural damage (volumetric changes).
Example
Upon consideration of the SiO2-Al2O3 phase diagram (figure 10.26) for the
following pair of compositions, which would you judge to be the more
desirable refractory? Justify your choice.
20wt% Al2O3-80 wt% SiO2
25 wt% Al2O3-75 wt% SiO2
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Piezoelectricity
• Lead zirconate titanate (Pb[ZrxTi1-x]O3 0<x<1) , also called PZT
• Barium strontium titanate
Perovskite structure
Transform energy of a mechanical input into an
electrical output. More specifically, when a pressure
[piezo is the Greek word for pressure] is applied to a
piezoelectric material, it causes a mechanical deformation
and a displacement of charges. Those charges are highly
proportional to the applied pressure [Piezoelectricity].
Deformation gives electric response;
Symmetry is broken and the three dipole moments no electric response can give change in shape
longer cancel - we have induced polarization by
(deformation)
mechanical deformation
http://wpcontent.answcdn.com/wikipedia/commons/th
umb/c/c4/SchemaPiezo.gif/220px-SchemaPiezo.gif
Structure controls properties
Piezoelectricity:
Applications – Transducers (a device that converts one type of energy to another)
http://images.machinedesign.com/ima
ges/archive/72087piezoelect_0000005
0053.jpg
Store charge as
you walk?!
+
http://4.bp.blogspot.com/_b5hcKABPlGI/SwI
PNBW7_xI/AAAAAAAAaeU/dxq_wNQi5I/s1600/11-1709b.jpg
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Metals + Ceramics: Hard Coatings
A thin film (.0001- .0004”)
Processed by
chemical vapor deposition
physical
p
y
vapor
p deposition
p
Can be ‘pure’ metals, alloyed metals or
ceramics
Ceramic coatings are most common due to
their hardness and good oxidation
properties on tool steels
Titanium Nitride
Titanium CarboNitride
Chromium Nitride
Titanium Nitride
Zirconium Nitride
Titanium Carbide
Titanium Carbide
Aluminum Nitride
To Coat or not to Coat?
Mild steel
Carbide insert
TiN coated carbide insert
Build up
Mild steel
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Zirconia (ZrO2)
•
ZrO2 adopts different phases at elevated temperature (-monoclinic, -tetragonal,
 – cubic).
– The volume expansion caused by the cubic to tetragonal to monoclinic
transformation induces very large stresses, and will cause pure ZrO2 to
crack upon cooling from high temperatures.
Phase diagram from Arroyave et al. CAPLHAD (2002)
Thermal Barrier Coatings (TBC)
http://www.me.jhu.edu/imagesMechE/research/hemker-1.jpg
http://www.matsceng.ohiostate.edu/faculty/padture/padturewebpage/padture/TBC.jpg
The cubic phase of zirconia has a very low thermal conductivity, which has
led to its use as a Thermal barrier coatings (TBC) in jet/diesel engines to allow
operation at higher temperatures. Thermodynamically the higher the operation
temperature of an engine, the greater the possible efficiency (see Carnot heat
engine). But engines go up and down in temperature – what can we do?
Engineer the material!
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Zirconia (ZrO2)
• Biomaterial: Acts as subframes for the
construction of dental restoration, such as
crowns and bridges
g
• High dielectric (k) material for
potential applications as an
insulator in transistors and future
nanoelectronics
• Diamond ‘replacement
‘(cubic zirconia): optical and
hardness
ZrO2
ZrO2
X
X
Gas Sensor
Electro-ceramic: “Stabilized” zirconia is used in oxygen sensors/fuel
cells membranes because it has the ability to allow oxygen ions to
move freely through the crystal structure at high temperatures. High
ionic conductivity (and a low electronic conductivity).
http://nano.tkk.fi/en/research_groups/electron_physics/research/gas_sensors02.jpg
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Summary:
• A ceramic is a metal + nonmetal
•An example:
p
SiC-Which is used for ceramic p
plating
g for bullet
proof vests.
•Metal and Ceramics can be combined to be used as a
hard coating.
•Some reasons to use hard coatings:
•Increased hardness
•Chemical Inertness
•Oxidation Resistance
•Increased lubricity
•Elimination of galling and pickup
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