Chapter 13: Applications and Processing of Ceramics ISSUES TO ADDRESS... • How do we classify ceramics? • What are some applications of ceramics? • How is processing of ceramics different than for metals? Chapter 13 - 1 Classification of Ceramics Ceramic Materials Glasses Clay Refractories products Abrasives Cements Advanced ceramics -optical -whiteware -bricks for -sandpaper -composites -engine -composite -structural high T -cutting -structural rotors (furnaces) -polishing reinforce valves -containers/ bearings Adapted from Fig. 13.1 and discussion in -sensors household Section 13.2-8, Callister & Rethwisch 8e. Chapter 13 - 2 Ceramics Application: Die Blanks • Die blanks: -- Need wear resistant properties! • Die surface: -- 4 mm polycrystalline diamond particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond gives uniform hardness in all directions to reduce wear. die Ao die Ad tensile force Adapted from Fig. 11.8(d), Callister & Rethwisch 8e. Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. Chapter 13 - 3 Ceramics Application: Cutting Tools • Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling • Materials: -- manufactured single crystal or polycrystalline diamonds in a metal or resin matrix. -- polycrystalline diamonds resharpen by microfracturing along cleavage planes. oil drill bits blades Single crystal diamonds polycrystalline diamonds in a resin matrix. Photos courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. Chapter 13 - 4 Ceramics Application: Sensors • Example: ZrO2 as an oxygen sensor 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 removes a Zr 4+ ion and an O2- ion. Add Ca impurity to ZrO2: -- increases O2- vacancies -- increases O2- diffusion rate • Operation: -- voltage difference produced when sensor gas with an reference O2- ions diffuse from the external unknown, higher gas at fixed O2surface through the sensor to the oxygen content oxygen content diffusion reference gas surface. -- magnitude of voltage difference partial pressure of oxygen at the + voltage difference produced! external surface Chapter 13 - 5 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): 2200 T(ºC) 3Al2O3-2SiO2 2000 Liquid (L) 1800 mullite alumina + L mullite +L crystobalite +L 1600 1400 mullite + crystobalite 0 20 alumina + mullite 40 60 80 100 Composition (wt% alumina) Fig. 12.27, Callister & Rethwisch 8e. (Fig. 12.27 adapted from F.J. Klug and R.H. Doremus, J. Am. Cer. Soc. 70(10), p. 758, 1987.) Chapter 13 - 6 Advanced Ceramics: Materials for Automobile Engines • Advantages: – Operate at high temperatures – high efficiencies – Low frictional losses – Operate without a cooling system – Lower weights than current engines • Disadvantages: – Ceramic materials are brittle – Difficult to remove internal voids (that weaken structures) – Ceramic parts are difficult to form and machine • Potential candidate materials: Si3N4, SiC, & ZrO2 • Possible engine parts: engine block & piston coatings Chapter 13 - 7 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 Chapter 13 - 8 Ceramic Fabrication Methods (i) PARTICULATE CEMENTATION GLASS FORMING FORMING • Blowing of Glass Bottles: • Pressing: plates, cheap glasses Gob Pressing operation Parison mold -- glass formed by application of pressure -- mold is steel with graphite lining • Fiber drawing: Compressed air Suspended parison Finishing mold Adapted from Fig. 13.8, Callister & Rethwisch 8e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.) wind up Chapter 13 - 9 Sheet Glass Forming • Sheet forming – continuous casting – sheets are formed by floating the molten glass on a pool of molten tin Adapted from Fig. 13.9, Callister & Rethwisch 8e. Chapter 13 - 10 Glass Structure • Basic Unit: 4Si0 4 tetrahedron Si 4+ O2- • Quartz is crystalline SiO2: Glass is noncrystalline (amorphous) • Fused silica is SiO2 to which no impurities have been added • Other common glasses contain impurity ions such as Na+, Ca2+, Al3+, and B3+ Na + Si 4+ O2- (soda glass) Adapted from Fig. 12.11, Callister & Rethwisch 8e. Chapter 13 - 11 Glass Properties • Specific volume (1/r) vs Temperature (T): • Crystalline materials: Specific volume Liquid (disordered) Supercooled Liquid • Glasses: Glass (amorphous solid) Crystalline (i.e., ordered) Tg -- crystallize at melting temp, Tm -- have abrupt change in spec. vol. at Tm Tm Adapted from Fig. 13.6, Callister & Rethwisch 8e. solid T -- do not crystallize -- change in slope in spec. vol. curve at glass transition temperature, Tg -- transparent - no grain boundaries to scatter light Chapter 13 - 12 Glass Properties: Viscosity • Viscosity, h: -- relates shear stress () and velocity gradient (dv/dy): dy glass dv dv dy h dv / dy velocity gradient h has units of (Pa-s) Chapter 13 - 13 Log Glass Viscosity vs. Temperature • Viscosity decreases with T • soda-lime glass: 70% SiO2 balance Na2O (soda) & CaO (lime) • borosilicate (Pyrex): 13% B2O3, 3.5% Na2O, 2.5% Al2O3 • Vycor: 96% SiO2, 4% B2O3 Viscosity [Pa-s] • fused silica: > 99.5 wt% SiO2 10 14 10 10 10 6 10 2 1 200 strain point annealing point Working range: glass-forming carried out Tmelt 600 1000 1400 1800 T(ºC) Adapted from Fig. 13.7, Callister & Rethwisch 8e. (Fig. 13.7 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.) Chapter 13 - 14 Heat Treating Glass • Annealing: -- removes internal stresses caused by uneven cooling. • Tempering: -- puts surface of glass part into compression -- suppresses growth of cracks from surface scratches. -- sequence: before cooling hot initial cooling at room temp. cooler hot cooler compression tension compression -- Result: surface crack growth is suppressed. Chapter 13 - 15 • Ceramic Fabrication techniques: -- glass forming (pressing, blowing, fiber drawing). -- particulate forming (hydroplastic forming, slip casting, powder pressing, tape casting) -- cementation Chapter 13 - 16 Ceramic Fabrication Methods (iia) GLASS FORMING PARTICULATE FORMING CEMENTATION Hydroplastic forming: • Mill (grind) and screen constituents: desired particle size • Extrude this mass (e.g., into a brick) Ao force container ram billet container die holder extrusion die Ad Adapted from Fig. 12.8(c), Callister & Rethwisch 8e. • Dry and fire the formed piece Chapter 13 - 17 Ceramic Fabrication Methods (iia) GLASS FORMING PARTICULATE FORMING CEMENTATION Slip casting: • Mill (grind) and screen constituents: desired particle size • Mix with water and other constituents to form slip • Slip casting operation pour slip into mold absorb water into mold “green ceramic” solid component pour slip into mold drain mold “green ceramic” Adapted from Fig. 13.12, Callister & Rethwisch 8e. (Fig. 13.12 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) hollow component • Dry and fire the cast piece Chapter 13 - 18 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 Chapter 13 - 19 Hydroplasticity of Clay • Clay is inexpensive • When water is added to clay Shear -- water molecules fit in between layered sheets -- reduces degree of van der Waals bonding -- when external forces applied – clay particles free to move past one another – becomes hydroplastic • Structure of Kaolinite Clay: Adapted from Fig. 12.14, Callister & Rethwisch 8e. (Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.) charge neutral weak van der Waals bonding 4+ charge neutral Si 3+ Al OH 2O Shear Chapter 13 - 20 Drying and Firing • Drying: as water is removed - interparticle spacings decrease – shrinkage . Adapted from Fig. 13.13, Callister & Rethwisch 8e. (Fig. 13.13 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) wet body partially dry completely dry • Firing: -- heat treatment between 900-1400ºC -- vitrification: liquid glass forms from clay and flux – flows between SiO2 particles. (Flux lowers melting temperature). micrograph of porcelain Drying too fast causes sample to warp or crack due to non-uniform shrinkage Si02 particle (quartz) glass formed around the particle 70mm Adapted from Fig. 13.14, Callister & Rethwisch 8e. (Fig. 13.14 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.) Chapter 13 - 21 Ceramic Fabrication Methods (iib) GLASS FORMING PARTICULATE FORMING CEMENTATION 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 ( Chapter 13 - 22 Sintering Sintering occurs during firing of a piece that has been powder pressed -- powder particles coalesce and reduction of pore size Adapted from Fig. 13.16, Callister & Rethwisch 8e. Aluminum oxide powder: -- sintered at 1700ºC for 6 minutes. Adapted from Fig. 13.17, Callister & Rethwisch 8e. (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.) 15 mm Chapter 13 - 23 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. 13.18, Callister & Rethwisch 8e. Chapter 13 - 24 Ceramic Fabrication Methods (iii) GLASS FORMING PARTICULATE FORMING CEMENTATION • 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 1400ºC) -- grind into fine powder Chapter 13 - 25 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) Chapter 13 - 26 ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 13 - 27