Ceramics

1. Ceramics

2. Taxonomy of Ceramics Glasses Clay Refractories Abrasives Cements Advanced products ceramics -bricks for -optical -whiteware -sandpaper -composites engine high T - composite - bricks - cutting - structural - rotors (furnaces) reinforce - polishing - valves - containers/ - bearings Adapted from Fig. 13.1 and discussion in Section 13.2-6, Callister 7e. household -sensors • Properties: -- Tm for glass is moderate, but large for other ceramics. -- Small toughness, ductility; large moduli & creep resist. • Applications: -- High T, wear resistant, novel uses from charge neutrality. • Fabrication -- some glasses can be easily formed -- other ceramics can not be formed or cast. 2

3. Application: Refractories 2200 3Al2O3-2SiO2 T(°C) mullite 2000 Liquid alumina + L (L) 1800 mullite alumina crystobalite + L + + L 1600 mullite mullite + crystobalite 1400 0 20 40 60 80 100 Composition (wt% alumina) • Need a material to use in high temperature furnaces. • Consider the Silica (SiO2) - Alumina (Al2O3) system. • Phase diagram shows: mullite, alumina, and crystobalite as candidate refractories. Adapted from Fig. 12.27, Callister 7e. (Fig. 12.27 is adapted from F.J. Klug and R.H. Doremus, "Alumina Silica Phase Diagram in the Mullite Region", J. American Ceramic Society70(10), p. 758, 1987.) 3

4. Application: Die Blanks die A d tensile A o force die • Die blanks: -- Need wear resistant properties! Adapted from Fig. 11.8 (d), Callister 7e. Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. • Die surface: -- 4 mm polycrystalline diamond particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond helps control fracture and gives uniform hardness in all directions. Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. 4

5. Application: Cutting Tools • Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling • Solutions: blades oil drill bits -- manufactured single crystal or polycrystalline diamonds in a metal or resin matrix. coated single crystal diamonds -- optional coatings (e.g., Ti to help diamonds bond to a Co matrix via alloying) polycrystalline diamonds in a resin matrix. -- polycrystalline diamonds resharpen by microfracturing along crystalline planes. Photos courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. 5

6. Application: Sensors 2+ Ca • Approach: Add Ca impurity to ZrO2: -- increases O2- vacancies -- increases O2- diffusion rate 2+ A Ca impurity 4+ removes a Zr and a 2 - O ion. • Operation: -- voltage difference produced when O2- ions diffuse from the external surface of the sensor to the reference gas. sensor gas with an reference unknown, higher gas at fixed 2- O oxygen content oxygen content diffusion - + voltage difference produced! • Example: Oxygen sensor ZrO2 • Principle: Make diffusion of ions fast for rapid response. 6

7. Glass & Vitreous Ceramics Glass Vitreous Ceramics

8. High-performance Engineering Ceramics Diamond: used as cutting tools, rock drills, abrasive, etc. Generic High-performance Ceramics

9. Cement and Concrete Cement: Mixture of lime (CaO), silica (SiO2) and alumina (Al2O3), which sets when mixed with water Concrete: Sand and stones held together by cement.

10. Natural Ceramics

11. Structure of Ceramics - Ionic MgO Structure: Can be thought of as an fcc packing with Mg ions in octahedral holes. NaCl Structure

12. Structure of Ceramics - Ionic Al2O3: c.p.h packing of O with Al in 2/3 of the octahedral holes ZrO2: fcc packing of Zr with O in the tetrahedral holes

13. Structure of Ceramics – Simple Covalent SiC: diamond structure with half the atoms replaced by Si. Diamond: each atom has four neighbors.

14. Structure of Ceramics – Simple Covalent Cubic SiO4: diamond structure with an SiO4 tetrahedron on each atom site.

15. Structure of Ceramics Microstructure of Ceramics

16. Mechanical Properties of Ceramics Elastic Moduli

17. Mechanical Properties of Ceramics Strength, Hardness & Lattice Resistance Normalised Hardness of Pure Metals, Alloys and Ceramics

18. Mechanical Properties of Ceramics Dislocation Movement Dislocation motion in covalent solids is intrinsically difficult because the interatomic bonds must be broken and reformed

19. Mechanical Properties of Ceramics Dislocation Movement Dislocation motion in ionic solids is easy on some planes, but hard on others. The hard systems usually dominate.

20. Mechanical Properties of Ceramics Fracture Strength of Ceramics The design strength of a ceramic is determined by fracture toughness and lengths of the microcracks it contains.

21. Mechanical Properties of Ceramics Fracture Strength of Ceramics (a) Tensile test measures tensile strength, TS (b) Bend test measures modulus of rupture, r, typically 1.7 TS (c) Compression test measures crushing strength, c, typically 15TS

22. Mechanical Properties of Ceramics- Fracture Strength In compression, many flaws propagate stably to give general crashing In tension the largest flaw propagates unstably

23. Mechanical Properties of Ceramics Thermal Shock Resistance ET = TS Where E is the Young’s modulus,  is the coefficient of expansion and TS is tensile strength. T represents the ceramic’s thermal shock resistance

24. Ceramic Fabrication Methods-I Pressing Gob operation Parison mold • Fiber drawing: Compressed • Blowing: air suspended Parison Finishing mold wind up PARTICULATEFORMING CEMENTATION GLASS FORMING • Pressing: plates, dishes, cheap glasses --mold is steel with graphite lining Adapted from Fig. 13.8, Callister, 7e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.) 24

25. Sheet Glass Forming Sheet forming – continuous draw originally sheet glass was made by “floating” glass on a pool of mercury Adapted from Fig. 13.9, Callister 7e. 25

26. Glass Structure 4- Si0 tetrahedron 4 4+ Si 2 - O + Na 4+ Si 2 - O • Basic Unit: • Glass is amorphous • Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+) • Impurities: interfere with formation of crystalline structure. • Quartz is crystalline SiO2: (soda glass) Adapted from Fig. 12.11, Callister, 7e. 26

27. Glass Properties Liquid Supercooled (disordered) Liquid Glass (amorphous solid) Crystalline (i.e., ordered) • Specific volume (1/r) vs Temperature (T): • Crystalline materials: -- crystallize at melting temp, Tm -- have abrupt change in spec. vol. at Tm Specific volume • Glasses: -- do not crystallize -- change in slope in spec. vol. curve at glass transition temperature, Tg -- transparent - no crystals to scatter light solid T T T g m Adapted from Fig. 13.6, Callister, 7e. 27

28. Glass Properties: Viscosity t dy dv glass dv dy t velocity gradient • Viscosity, h: -- relates shear stress and velocity gradient: hhas units of (Pa-s) 28

29. Glass Viscosity vs. T and Impurities fused silica glass 96% silica soda-lime Pyrex s] × 14 10 strain point annealing range 10 10 Viscosity [Pa 6 T : soft enough 10 deform to deform or “work” 2 10 Tmelt 1 T(°C) 200 600 1000 1400 1800 • soda-lime glass: 70% SiO2 balance Na2O (soda) & CaO (lime) • Viscosity decreases with T • Impurities lower Tdeform • borosilicate (Pyrex): 13% B2O3, 3.5% Na2O, 2.5% Al2O3 • Vycor: 96% SiO2, 4% B2O3 • fused silica: > 99.5 wt% SiO2 Adapted from Fig. 13.7, Callister, 7e. (Fig. 13.7 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.) 29

30. Heat Treating Glass before cooling surface cooling further cooled compression cooler hot hot tension compression cooler --Result: surface crack growth is suppressed. • Annealing: --removes internal stress caused by uneven cooling. • Tempering: --puts surface of glass part into compression --suppresses growth of cracks from surface scratches. --sequence: 30

31. Ceramic Fabrication Methods-IIA GLASSFORMING PARTICULATE FORMING CEMENTATION Adapted from Fig. 11.8 (c), Callister 7e. --Hydroplastic forming: extrude the slip (e.g., into a pipe) --Slip casting: drain pour slip pour slip “green absorb water mold Adapted from Fig. 13.12, Callister 7e. (Fig. 13.12 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) into mold A into mold into mold ceramic” o “green container die holder ceramic” force ram A billet extrusion d die container solid component hollow component • Milling and screening: desired particle size • Mixing particles & water: produces a "slip" • Form a "green" component • Dry and fire the component 31

32. Clay Composition A mixture of components used (50%) 1. Clay (25%) 2. Filler – e.g. quartz (finely ground) (25%) 3. Fluxing agent (Feldspar) binds it together aluminosilicates + K+, Na+, Ca+ 32

33. Features of a Slip Shear charge neutral weak van der Waals bonding 4+ charge Si 3 + neutral Al - OH 2- O Shear • 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 7e. (Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.) 33

34. Drying and Firing wet slip partially dry “green” ceramic • Firing: --T raised to (900-1400°C) --vitrification: liquid glass forms from clay and flows between SiO2 particles. Flux melts at lower T. Adapted from Fig. 13.14, Callister 7e. (Fig. 13.14 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.) Si02 particle (quartz) micrograph of glass formed porcelain around the particle 70mm • Drying: layer size and spacing decrease. Adapted from Fig. 13.13, Callister 7e. (Fig. 13.13 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) Drying too fast causes sample to warp or crack due to non-uniform shrinkage 34

35. Ceramic Fabrication Methods-IIB GLASSFORMING PARTICULATE FORMING CEMENTATION 15m Sintering: useful for both clay and non-clay compositions. • Procedure: -- produce ceramic and/or glass particles by grinding -- place particles in mold -- press at elevated T to reduce pore size. • Aluminum oxide powder: -- sintered at 1700°C for 6 minutes. Adapted from Fig. 13.17, Callister 7e. (Fig. 13.17 is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.) 35

36. Powder Pressing Sintering - powder touches - forms neck & gradually neck thickens add processing aids to help form neck little or no plastic deformation • Uniaxial compression - compacted in single direction • Isostatic(hydrostatic) compression - pressure applied by fluid - powder in rubber envelope • Hot pressing - pressure + heat Adapted from Fig. 13.16, Callister 7e. 36

37. Tape Casting thin sheets of green ceramic cast as flexible tape used for integrated circuits and capacitors cast from liquid slip (ceramic + organic solvent) Adapted from Fig. 13.18, Callister 7e. 37

38. Ceramic Fabrication Methods-III GLASSFORMING PARTICULATE FORMING CEMENTATION • Produced in extremely large quantities. • Portland cement: -- mix clay and lime bearing materials -- calcinate (heat to 1400°C) -- primary constituents: tri-calcium silicate di-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. 38

39. Applications: Advanced Ceramics Heat Engines Advantages: Run at higher temperature Excellent wear & corrosion resistance Low frictional losses Ability to operate without a cooling system Low density • Disadvantages: • Brittle • Too easy to have voids- weaken the engine • Difficult to machine • Possible parts – engine block, piston coatings, jet engines • Ex: Si3N4, SiC, & ZrO2 39

40. Applications: Advanced Ceramics Ceramic Armor Al2O3, B4C, SiC & TiB2 Extremely hard materials shatter the incoming projectile energy absorbent material underneath 40

41. Applications: Advanced Ceramics Electronic Packaging Chosen to securely hold microelectronics & provide heat transfer Must match the thermal expansion coefficient of the microelectronic chip & the electronic packaging material. Additional requirements include: good heat transfer coefficient poor electrical conductivity Materials currently used include: Boron nitride (BN) Silicon Carbide (SiC) Aluminum nitride (AlN) thermal conductivity 10x that for Alumina good expansion match with Si 41