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Chapter 13-
Need a material to use in high temperature furnaces.
Consider Silica (SiO2) - Alumina (Al2O3) system. Phase diagram shows:
mullite, alumina, and crystobalite (made up of SiO2)tetrahedra as candidate refractories.
3Composition (wt% alumina)
T(C)
1400
1600
1800
20 00
2200
20 40 60 80 1000
alumina +
mullite
mullite+ L
mulliteLiquid
(L)
mullite
+ crystobalite
crystobalite+ L
alumina + L
3Al2O3-2SiO 2
Adapted from Fig. 12.27,Callister 6e. (Fig. 12.27is adapted from F.J. Klug
and R.H. Doremus,"Alumina Silica PhaseDiagram in the MulliteRegion", J. AmericanCeramic Society70(10),p. 758, 1987.)
APPLICATION: REFRACTORIES
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tensile
forceAo
Addie
die
Die blanks:--Need wear resistant properties!
4
Die surface:--4 mm polycrystalline diamond
particles that are sintered on to acemented tungsten carbidesubstrate.
--polycrystalline diamond helps controlfracture and gives uniform hardnessin all directions.
Courtesy Martin Deakins, GESuperabrasives, Worthington,OH. Used with permission.
Adapted from Fig.11.7, Callister 6e.
Courtesy Martin Deakins, GESuperabrasives, Worthington,
OH. Used with permission.
APPLICATION: DIE BLANKS
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Chapter 13- 5
Tools:--for grinding glass, tungsten,
carbide, ceramics--for cutting Si wafers--for oil drilling
bladesoil drill bits Solutions:
--manufactured single crystalor polycrystalline diamondsin a metal or resin matrix.
--optional coatings (e.g., Ti to helpdiamonds bond to a Co matrixvia alloying)
--polycrystalline diamondsresharpen by microfracturing
along crystalline planes.
coated singlecrystal diamonds
polycrystallinediamonds in a resinmatrix.
Photos courtesy Martin Deakins,GE Superabrasives, Worthington,OH. Used with permission.
APPLICATION: CUTTING TOOLS
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Chapter 13- 6
Ex: Oxygen sensor: ZrO2 Principle: Make diffusion of ions
fast for rapid response.
Approach:Add Ca impurity to:
--increase O2-
vacancies--increase O2- diffusion
Operation:--voltage difference
produced when
O2-
ions diffusebetween externaland referencesgases.
reference
gas at fixed
oxygen content
O2-
diffus
ion
gas with an
unknown, higher
oxygen content
-+voltage difference produced!
sensor
APPLICATION: SENSORS
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Chapter 13- 7
Pressing:
GLASSFORMING
Gob
Parison
mold
Pressing
operation
Blowing:
Fiber drawing:
Adapted from Fig. 13.7, Callister, 6e. (Fig. 13.7 is adapted from C.J. Phillips,Glass: The Miracle Maker, Pittman Publishing Ltd., London.)
CERAMIC FABRICATION METHODS-I
wind up
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Quartz is crystallineSiO2:
Basic Unit:
Si0 4 tetrahedron4-
Si4+
O2-
Glass is amorphous
Amorphous structureoccurs by adding impurities
(Na+,Mg2+,Ca2+, Al3+)
Impurities:interfere with formation ofcrystalline structure.
(soda glass)
Adapted from Fig. 12.11,Callister, 6e.
GLASS STRUCTURE
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Chapter 13- 9
Specific volume (1/r) vs Temperature (T):
Glasses:--do not crystallize
--spec. vol. varies smoothly with T
--Glass transition temp, Tg
Crystalline materials:--crystallize at melting temp, Tm--have abrupt change in spec.
vol. at Tm
Viscosity:--relates shear stress &
velocity gradient:--has units of (Pa-s)
dv
dy
Adapted from Fig. 13.5, Callister, 6e.
GLASS PROPERTIES
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Viscosity decreases with T
Impurities lower Tdeform
Adapted from Fig. 13.6, Callister, 6e.(Fig. 13.6 is from E.B. Shand, EngineeringGlass, Modern Materials, Vol. 6, AcademicPress, New York, 1968, p. 262.)
GLASS VISCOSITY VS T AND IMPURITIES
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Annealing:
--removes internal stress caused by uneven cooling. Tempering:
--puts surface of glass part into compression--suppresses growth of cracks from surface scratches.--sequence:
--Result: surface crack growth is suppressed.
further cooledbefore cooling surface cooling
tension
compression
compression
hot hot
cooler
cooler
HEAT TREATING GLASS
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Milling and screening: desired particle size
PARTICULATEFORMING
Mixing particles & water: produces a "slip"
--Hydroplastic forming:extrude the slip (e.g., into a pipe)
12
Form a "green" component
hollow component
Dry and Fire the component
--Slip casting:
solid component
Adapted fromFig. 11.7,Callister 6e.
Adapted from Fig.13.10, Callister 6e.(Fig. 13.10 is fromW.D. Kingery,Introduction toCeramics, JohnWiley and Sons,Inc., 1960.)
CERAMIC FABRICATION METHODS-IIA
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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 6e.(Fig. 12.14 is adapted from W.E. Hauth,"Crystal Chemistry of Ceramics", AmericanCeramic Society Bulletin, Vol. 30 (4), 1951,p. 140.)
FEATURES OF A SLIP
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Firing:--T raised to (900-1400 C)--vitrification: glass forms from clay and flows between
SiO2 particles.
Drying: layer size and spacing decrease.Adapted from Fig.
13.11, Callister 6e.(Fig. 13.11 is fromW.D. Kingery,Introduction toCeramics, JohnWiley and Sons,Inc., 1960.)
Adapted from Fig. 13.12,
Callister 6e.(Fig. 13.12 is courtesy H.G.Brinkies, SwinburneUniversity of Technology,Hawthorn Campus,Hawthorn, Victoria,Australia.)
DRYING AND FIRING
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Sintering: useful for both clay and non-clay compositions. Procedure:
--grind to produce ceramic and/or glass particles--inject into mold--press at elevated T to reduce pore size.
Aluminum oxide powder:--sintered at 1700C
for 6 minutes.
PARTICULATEFORMING
15
Adapted from Fig. 13.15, Callister 6e.(Fig. 13.15 is from W.D. Kingery, H.K.Bowen, and D.R. Uhlmann, Introductionto Ceramics, 2nd ed., John Wiley andSons, Inc., 1976, p. 483.)
CERAMIC FABRICATION METHODS-IIB
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Chapter 13-
CEMENTATION
Produced in extremely large quantities. Portland cement:
--mix clay and lime bearing materials--calcinate (heat to 1400C)--primary constituents:
tri-calcium silicatedi-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.16
CERAMIC FABRICATION METHODS-III
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Reading:
Core Problems:
Self-help Problems:
0
ANNOUNCEMENTS