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Ceramic Their Properties and Material Behavior

Ceramic Their Properties and Material Behavior. Engr 2110 Dr. R. Lindeke. Taxonomy of Ceramics. Glasses. Clay . Refractories. Abrasives. Cements. Advanced . products. ceramics. -bricks for . -optical . -whiteware . -sandpaper . -composites . engine . high T . -. composite . -.

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Ceramic Their Properties and Material Behavior

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  1. Ceramic Their Properties and Material Behavior Engr 2110 Dr. R. Lindeke

  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.

  3. Ceramic Bonding CaF2: large SiC: small • Bonding: -- Mostly ionic, some covalent. -- % ionic character increases with difference in electronegativity (remember!?!). • Large vs small ionic bond character: Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.

  4. Ceramic Crystal Structures Oxide structures • oxygen anions much larger than metal cations • close packed oxygen in a lattice (usually FCC) • cations in the holes of the oxygen lattice • The same ideas apply to all “ceramics” • Principles of Ceramic Architecture: • Size relationships Cation to Anion • Electrical Neutrality of the overall structure • Crystallographic Arrangements • Stoichiometry Must Match

  5. Silica Glass • A “Dense form” of amorphous silica • Charge imbalance corrected with “counter cations” such as Na+ • Borosilicate glass is the pyrex glass used in labs • better temperature stability & less brittle than sodium glass

  6. Table 13.1 GLASSES – transparent and easily shaped Noncrystalline Silicates + oxides (CaO, Na2O, K2O, Al2O3) E.g. Soda lime glass = 70wt% SiO2 + 30% [Na2O (soda) and CaO(lime)

  7. GLASS PROPERTIES • Viscosity: --relates shear stress & velocity gradient: --has units of (Pa-s) • Specific volume (1/r) vs Temperature (T): • Crystalline materials: --crystallize at melting temp, Tm --have abrupt change in spec. vol. at Tm • Glasses: --do not crystallize --spec. vol. varies smoothly with T --Glass transition temp, Tg Adapted from Fig. 13.5, Callister, 6e. 9

  8. GLASS VISCOSITY VS T AND IMPURITIES from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262. • Viscosity decreases with T increase • Impurities lower Tdeform 10

  9. Important Temperatures • Melting point = viscosity of 10 Pa.s • Working point= viscosity of 1000 Pa.s • Softening point= viscosity of 4x107Pa.s • Temperature above which glass cannot • be handled without altering dimensions) • Annealing point= viscosity of 1012 Pa.s. • Strain point = viscosity of 3x1013Pa.s • Fracture occurs before deformation • Viscosity decreases with T • Impurities lower Tdeform

  10. Silicates • Combine SiO44- tetrahedra by having them share corners, edges, or faces • Cations such as Ca2+, Mg2+, & Al3+ act to neutralize & provide ionic bonding Mg2SiO4 Ca2MgSi2O7

  11. = Layered Silicates • Layered silicates (clay silicates) • SiO4 tetrahedra connected together to form 2-D plane • (Si2O5)2- • So need cations to balance charge

  12. Layered Silicates • Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)42+ layer Adapted from Fig. 12.14, Callister 7e. Note: these sheets loosely bound by van der Waal’s forces

  13. Layered Silicates • Can change the counterions • this changes layer spacing • the layers also allow absorption of water • Micas: KAl3Si3O10(OH)2 • Bentonite • used to seal wells • packaged dry • swells 2-3 fold in H2O • pump in to seal up well so no polluted ground water seeps in to contaminate the water supply. • Used in bonding Foundry Sands and Taconite pellets

  14. Carbon Forms • Carbon black – amorphous – surface area ca. 1000 m2/g • Diamond • tetrahedral carbon • hard – no good slip planes • brittle – can cleave (cut) it • large diamonds – jewelry • small diamonds • often man made - used for cutting tools and polishing • diamond films • hard surface coat – cutting tools, medical devices, etc.

  15. Carbon Forms - Graphite • layer structure – aromatic layers • weak van der Waal’s forces between layers • planes slide easily, good lubricant

  16. Carbon Forms – Fullerenes and Nanotubes • Fullerenes or carbon nanotubes • wrap the graphite sheet by curving into ball or tube • Buckminister fullerenes • Like a soccer ball C60 - also C70 + others Adapted from Figs. 12.18 & 12.19, Callister 7e.

  17. Defects in Ceramic Structures Shottky Defect: Frenkel Defect • Frenkel Defect --a cation is out of place. • Shottky Defect --a paired set of cation and anion vacancies. Adapted from Fig. 12.21, Callister 7e. (Fig. 12.21 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.) • Equilibrium concentration of defects

  18. Mechanical Properties We know that ceramics are more brittle than metals. Why? • Consider method of deformation • slippage along slip planes • in ionic solids this slippage is very difficult • too much energy needed to move one anion past another anion (like charges repel)

  19. Measuring Elastic Modulus F cross section L/2 L/2 d R b d = midpoint rect. circ. deflection • Determine elastic modulus according to: F 3 3 F L F L = = E x 3 4 d d p F 4 bd 12 R slope = rect. circ. d cross cross d section section linear-elastic behavior • Room T behavior is usually elastic, with brittle failure. • 3-Point Bend Testing often used. --tensile tests are difficult for brittle materials! Adapted from Fig. 12.32, Callister 7e.

  20. Measuring Strength F cross section L/2 L/2 d R b location of max tension d = midpoint rect. circ. deflection • Typ. values: • Flexural strength: s Material (MPa) E(GPa) fs 1.5Ff L Ff L s = = Si nitride Si carbide Al oxide glass (soda) 250-1000 100-820 275-700 69 304 345 393 69 fs bd2 pR3 rect. F x Ff Data from Table 12.5, Callister 7e. d d fs • 3-point bend test to measure room T strength. Adapted from Fig. 12.32, Callister 7e.

  21. Mechanical Issues: • Properties are significantly dependent on processing – and as it relates to the level of Porosity: • E = E0(1-1.9P+0.9P2) – P is fraction porosity • fs = 0e-nP -- 0 & n are empirical values • Because the very unpredictable nature of ceramic defects, we do not simply add a factor of safety for tensile loading • We may add compressive surface loads • We often choose to avoid tensile loading at all – most ceramic loading of any significance is compressive (consider buildings, dams, brigdes and roads!)

  22. 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.)

  23. 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.

  24. 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.

  25. 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.

  26. Alternative Energy – Titania Nano-Tubes "This is an amazing material architecture for water photolysis," says Craig Grimes, professor of electrical engineering and materials science and engineering. Referring to some recent finds of his research group (G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, C. A. Grimes, Enhanced Photocleavage of Water Using Titania Nanotube-Arrays, Nano Letters, vol. 5, pp. 191-195.2005 ), "Basically we are talking about taking sunlight and putting water on top of this material, and the sunlight turns the water into hydrogen and oxygen. With the highly-ordered titanium nanotube arrays, under UV illumination you have a photoconversion efficiency of 13.1%. Which means, in a nutshell, you get a lot of hydrogen out of the system per photon you put in. If we could successfully shift its bandgap into the visible spectrum we would have a commercially practical means of generating hydrogen by solar energy.

  27. 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.)

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

  29. Modern Plate/Sheet Glass making: Image from Prof. JS Colton, Ga. Institute of Technology

  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:

  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

  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+

  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.)

  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

  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.)

  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.

  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.

  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.

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

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

  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

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