chapter 13 avi

8/3/2019 Chapter 13 Avi

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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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Chapter 13-

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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Chapter 13- 8

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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Chapter 13- 10

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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Chapter 13- 11

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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Chapter 13-

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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Chapter 13- 13

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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Chapter 13- 14

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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Chapter 13-

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

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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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Chapter 13-

Reading:

Core Problems:

Self-help Problems:

0

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