Lecture 19 Chapter 13: Applications and Processing of Ceramics

ENGR 151 Materials of Engineering LECTURE 19 CHAPTER 13: APPLICATIONS AND PROCESSING OF CERAMICS

TOPICS TO ADDRESS... • How do we classify ceramics?

• What are some applications of ceramics?

• How is processing of ceramics different than for metals?

2 CLASSIFICATION OF CERAMICS

3 CLASSIFICATION OF CERAMICS

Ceramic Materials

Glasses Clay Refractories Abrasives Cements Advanced products ceramics

-optical -whiteware -bricks for -sandpaper -composites -engine - composite - structural high T - cutting - structural rotors reinforce (furnaces) - polishing valves - containers/ bearings Adapted from Fig. 13.1 and discussion in household Section 13.2-8, Callister & Rethwisch 9e. -sensors

4 CERAMICS APPLICATION: DIE BLANKS

• Die blanks: die A d tensile -- Need wear resistant properties! A o force die • Die surface: Adapted from Fig. 11.9(d), -- 4 μm polycrystalline diamond Callister & Rethwisch 9e. particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond gives uniform hardness in all directions to reduce wear.

Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

5 CERAMICS APPLICATION: CUTTING TOOLS • Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling • Materials: oil drill bits blades -- manufactured single crystal or polycrystalline diamonds Single crystal in a metal or resin matrix. diamonds -- polycrystalline diamonds polycrystalline resharpen by microfracturing diamonds in a resin along cleavage planes. matrix. Photos courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

6 CERAMICS APPLICATION: SENSORS • Example: ZrO as an oxygen sensor 2 Ca 2+ • Principle: Increase diffusion rate of oxygen to produce rapid response of sensor signal to change in oxygen concentration • Approach: A substituting Ca2+ ion 4+ removes a Zr ion and Add Ca impurity to ZrO2: an O2- ion. -- increases O2- vacancies -- increases O2- diffusion rate • Operation: sensor -- voltage difference produced when gas with an reference O2- ions diffuse from the external unknown, higher gas at fixed O 2- oxygen content oxygen content surface through the sensor to the diffusion reference gas surface. -- magnitude of voltage difference + -  partial pressure of oxygen at the voltage difference produced! external surface 7 GLASSES GLASS-CERAMICS

• Transformation from amorphous state to crystalline state via a process called crystallization. • Fine-grained polycrystalline material – glass- ceramic. • Grain formation is via a phase transformation. • Properties: • High mechanical strength • Low coefficients of thermal expansion • Relatively high temperature capabilities • Good dielectric properties (electrical insulators) • Good biological properties • Can be made optically transparent • E.g. Pyroceram, CorningWare, Cercor, Vision REFRACTORIES • Materials that withstand high temperatures without melting or decomposing (chemically, for example).

• Unreactive and inert when exposed to severe environments.

• Ability to provide thermal insulation.

• Applications: • Furnace linings for metal refining • Glass manufacturing • Metallurgical heat treatment • Power generation

10 REFRACTORIES

11 REFRACTORIES

• Materials to be used at high temperatures (e.g., in high temperature furnaces). • Consider the Silica (SiO2) - Alumina (Al2O3) system. • Silica refractories - silica rich - small additions of alumina depress melting temperature (phase diagram) and must be minimized: 2200 3Al2O3-2SiO2 T(ºC) mullite 2000 Liquid (L) alumina + L 1800 Fig. 12.25, Callister & Rethwisch 9e. mullite [Adapted from F. J. Klug, S. Prochazka, and crystobalite alumina R. H. Doremus, “Alumina–Silica Phase + L Diagram in the Mullite Region,” J. Am. + L + Ceram. Soc., 70[10], 758 (1987). Reprinted 1600 mullite by permission of the American Ceramic mullite Society.] + crystobalite 1400 0 20 40 60 80 100 Composition (wt% alumina) 12 REFRACTORIES – ABRASIVES AND CEMENTS

• Abrasives: Used to wear, grind or cut away softer material. • E.g.: • Diamond (natural and synthetic) – expensive • Silicon carbide, tungsten carbide (WC), aluminum oxide (corundum), silica sand

• Cements: when mixed with water, form a paste that eventually sets and hardens. • E.g. Portland cement

13 ADVANCED CERAMICS: MATERIALS FOR AUTOMOBILE ENGINES

 Advantages: • Disadvantages:  Operate at high – Ceramic materials are temperatures – high brittle efficiencies – Difficult to remove internal  Low frictional losses voids (that weaken structures)  Operate without a cooling system – Ceramic parts are difficult to form and machine  Lower weights than current engines

• Potential candidate materials: Si3N4, SiC, & ZrO2 • Possible engine parts: engine block & piston coatings

14 ADVANCED CERAMICS: MATERIALS FOR CERAMIC ARMOR Components: -- Outer facing plates -- Backing sheet

Properties/Materials: -- Facing plates -- hard and brittle — fracture high-velocity projectile

— Al2O3, B4C, SiC, TiB2 -- Backing sheets -- soft and ductile — deform and absorb remaining energy — aluminum, synthetic fiber laminates

15 ADVANCED CERAMICS: MEMS

• Microelectromechanical Systems • Miniaturized smart systems – highly integrated • Fabrication techniques – similar to integrated circuits

16 NANOCARBONS

 Fullerenes – spherical cluster of 60 carbon atoms, C60  Like a soccer ball  Carbon nanotubes – sheet of graphite rolled into a tube  Ends capped with fullerene hemispheres

Fig. 12.19, Callister & Rethwisch 8e.

Fig. 13.7, Callister & Rethwisch 9e. 17 NANOCARBONS (CONT.)

 Graphene – single-atomic-layer of graphite  composed of hexagonally sp2 bonded carbon atoms

Fig. 13.9, Callister & Rethwisch 9e.

18 NANOCARBONS (CONT.)

 Applications: Medicine, textiles, alloys, springs, coatings and films, radar absorption material, electronics

19 CERAMIC FABRICATION METHODS

20 CERAMIC FABRICATION METHODS (I)

GLASS PARTICULATE CEMENTATION FORMING FORMING • Blowing of Glass Bottles: • Pressing: plates, cheap glasses Pressing Gob -- glass formed by application of operation pressure Parison -- mold is steel with graphite mold lining • Fiber drawing: Compressed air

Suspended parison

Finishing wind up mold Fig. 13.13, Callister & Rethwisch 9e. (Adapted from C.J. Phillips, Glass: The Miracle Maker. Reproduced by permission of Pittman Publishing Ltd., London.) 21 SHEET GLASS FORMING

 Sheet forming – continuous casting  sheets are formed by floating the molten glass on a pool of molten tin

Fig. 13.14, Callister & Rethwisch 9e. (Courtesy of Pilkington Group Limited.)

22 GLASS STRUCTURE • Basic Unit: Glass is noncrystalline (amorphous)

4- • Fused silica is SiO2 to which no Si0 4 tetrahedron impurities have been added Si 4+ • Other common glasses contain O 2 - impurity ions such as Na+, Ca2+, Al3+, and B3+

• Quartz is crystalline Na + SiO2: Si 4+ O 2 -

(soda glass)

Adapted from Fig. 12.11, Callister & Rethwisch 9e.

23 GLASS PROPERTIES

• Specific volume (1/ρ) vs Temperature (T ): • Crystalline materials: Specific volume -- crystallize at melting temp, Tm -- have abrupt change in spec. Supercooled Liquid vol. at T Liquid (disordered) m

Glass • Glasses: (amorphous solid) -- do not crystallize Crystalline -- change in slope in spec. vol. curve at (i.e., ordered) solid glass transition temperature, Tg T Tg Tm -- transparent - no grain boundaries to scatter light Adapted from Fig. 13.11, Callister & Rethwisch 9e.

24 GLASS PROPERTIES: VISCOSITY

• Viscosity, η: -- relates shear stress (τ) and velocity gradient (dv/dy):

dy dv glass dv dy τ velocity gradient

η has units of (Pa-s)

25 LOG GLASS VISCOSITY VS. TEMPERATURE

• soda-lime glass: 70% SiO • Viscosity decreases with T 2 balance Na2O (soda) & CaO (lime) • borosilicate (Pyrex):

13% B2O3, 3.5% Na2O, 2.5% Al2O3

• Vycor: 96% SiO2, 4% B2O3

• fused silica: > 99.5 wt% SiO2

s] 10 strain point - annealing point 10 10

10 6 Working range: glass-forming carried out 2 10 Fig. 13.12, Callister & Rethwisch 9e. Viscosity [Pa Viscosity Tmelt (From E.B. Shand, Engineering Glass, 1 Modern Materials, Vol. 6, Academic Press, 200 600 1000 1400 1800 T(ºC) New York, 1968, p. 262.)

26 HEAT TREATING GLASS • Annealing: -- removes internal stresses caused by uneven cooling (thermal stresses due to poor thermal conductivity). • Tempering: -- puts surface of glass part into compression -- suppresses growth of cracks from surface scratches. -- sequence: before cooling initial cooling at room temp. cooler compression hot hot tension cooler compression -- Result: surface crack growth is suppressed.

27 CERAMIC FABRICATION METHODS (IIA)

GLASS PARTICULATE CEMENTATION FORMING FORMING Hydroplastic forming: • Mill (grind) and screen constituents: desired particle size • Mix with water • Extrude this mass (e.g., into a brick) A o container die holder force Fig. 11.9 (c), ram billet extrusion A d Callister & Rethwisch 9e. container die

• Dry and fire the formed piece • E.g. Brick, tiles, pipes, ceramic blocks

28 CERAMIC FABRICATION METHODS (IIA)

GLASS PARTICULATE CEMENTATION FORMING FORMING Slip casting: • Mill (grind) and screen constituents: desired particle size • Mix with water and other constituents to form slip • Slip casting operation pour slip absorb water pour slip drain “green into mold into mold into mold mold ceramic” Fig. 13.17, Callister “green & Rethwisch 9e. ceramic” (From W.D. Kingery, Introduction to Ceramics, Copyright © 1960 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) solid component hollow component • Dry and fire the cast piece 29 TYPICAL PORCELAIN COMPOSITION

(50%) 1. Clay (25%) 2. Filler – e.g. quartz (finely ground) (25%) 3. Fluxing agent (Feldspar) -- aluminosilicates plus K+, Na+, Ca+ -- upon firing - forms low-melting-temp. glass

30 HYDROPLASTICITY OF CLAY • Clay is inexpensive Shear • When water is added to clay -- water molecules fit in between layered sheets charge -- reduces degree of van der Waals neutral bonding -- when external forces applied – clay particles free to move past one weak van another – becomes hydroplastic der Waals • Structure of bonding 4+ Kaolinite Clay: charge Si 3+ Fig. 12.14, Callister & Rethwisch 9e. neutral Al [Adapted from W.E. Hauth, "Crystal Chemistry - of Ceramics", American Ceramic Society OH Bulletin, Vol. 30 (4), 1951, p. 140.] O 2-

Shear 31 DRYING AND FIRING • Drying: as water is removed - interparticle spacings decrease – shrinkage . Fig. 13.18, Callister & Rethwisch 9e. (From W.D. Kingery, Introduction to Ceramics, Copyright © 1960 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) wet body partially dry completely dry

Drying too fast causes sample to warp or crack due to non-uniform shrinkage

Si02 particle • Firing: (quartz) -- heat treatment between glass formed 900-1400°C around -- vitrification: liquid glass forms the particle

from clay and flux – flows micrograph of porcelain porcelain of micrograph

between SiO2 particles. (Flux 70 μm Fig. 13.19, Callister & Rethwisch 9e. lowers melting temperature). (Courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.) 32 CERAMIC FABRICATION METHODS (IIB)

GLASS PARTICULATE CEMENTATION FORMING FORMING

Powder Pressing: used for both clay and non-clay compositions.

• Powder (plus binder) compacted by pressure in a mold -- Uniaxial compression - compacted in single direction -- Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope -- Hot pressing - pressure + heat

33 SINTERING Sintering occurs during firing of a piece that has been powder pressed -- powder particles coalesce and reduction of pore size

Fig. 13.21, Callister & Rethwisch 9e. Aluminum oxide powder:

-- sintered at 1700°C Fig. 13.22, Callister & Rethwisch 9e. for 6 minutes. (From W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to Ceramics, 2nd edition, p. 483. Copyright © 1976 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.)

15 μm 34 TAPE CASTING

 Thin sheets of green ceramic cast as flexible tape  Used for integrated circuits and capacitors  Slip = suspended ceramic particles + organic liquid (contains binders, plasticizers)

Fig. 13.23, Callister & Rethwisch 9e. 35 CERAMIC FABRICATION METHODS (III)

GLASS PARTICULATE CEMENTATION FORMING FORMING • Hardening of a paste – paste formed by mixing cement material with water • Formation of rigid structures having varied and complex shapes • Hardening process – hydration (complex chemical reactions involving water and cement particles) • Portland cement – production of: -- mix clay and lime-bearing minerals -- calcine (heat to 1400°C) -- grind into fine powder

36 SUMMARY

• Categories of ceramics: -- glasses -- clay products -- refractories -- cements -- advanced ceramics • Ceramic Fabrication techniques: -- glass forming (pressing, blowing, fiber drawing). -- particulate forming (hydroplastic forming, slip casting, powder pressing, tape casting) -- cementation • Heat treating procedures -- glasses—annealing, tempering -- particulate formed pieces—drying, firing (sintering)