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), Callister & Rethwisch 9e. -- 4 μm polycrystalline diamond 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 diamonds in a metal or resin matrix. -- 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): τ 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 14 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.