chapter8 - CHAPTER 8 CERAMICS, GRAPHITE, AND DIAMOND:...

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Unformatted text preview: CHAPTER 8 CERAMICS, GRAPHITE, AND DIAMOND: STRUCTURE, GENERAL PROPERTIES, AND APPLICATIONS 8-1 Ceramics, Definition Compounds of metallic and nonmetallic elements Ceramics, Early History Pottery and bricks, before 4000BC Clay (Keramos) Ceramics, Classification Traditional Ceramics Engineering (Industrial) Ceramics Table 8.1 8-2 Hight—strength alumina for (b) Gas-turbine rotors made of silicon nitride. FIGURE 8.1 A variety of ceramic components. (a) high-temperature applications. source: Wesgo Div., GTE. 8-3 Structure Complex, and covalent (electron sharing), and ionic (oppositely charger ions) Single crystal or polycrystalline, Raw Material Clay Alumina (A1203) Zirconia (ZrOz) Partially Stabilized Zirconia (PSZ), (TTZ) Carbides, Tungsten (WC), Titanium (TiC), Silicon Carbide (SiC) Nitrides Cubic boron nitride (CBN) —— very hard Titanium nitride (TiN) Silicon nitride (Si3N4) 8-4 CATEGORIES AND uses 0F CERAMICS M Q TRADITIONAL CERAMICS M Abrasive products Abrasive wheels, emery cloth and sand paper, nozzles for sandblasting, ball milling Clay products Brick, pottery, sewer pipe Construction Brick, concrete, tile, plaster, glass Glass Bottles, laboratory ware, glazing Refractories Brick, crucibles, molds, cement Whitewares Dishes, tiles, plumbing, enamels ______________——..____————————u———————- ENGINEERING CERAMICS __________________.._....—_——_—-————-—-——-—————- Automotive and aerospace Turbine components, heat shields and exchangers, reentry components, seals Electronics Semiconductors, insulators, transducers, lasers, dielectrics, heating elements High temperature Refractories, brazing fixtures. kilns Manufacturing Cutting tools, wear and corrosion resistant components, glass ceramics, magnets, fiber optics Medical Laboratory ware, controls, prosthetics, dental _______________,____________._#_——————-— 8—5 Cermets A1203 + TiC Powder-metallurgy General Properties UTS z UTSoe'np Where: p = the volume fraction of pores in the solid UT So = ultimate strength at zero porosity n = a material constant, 4 to 7 E z E0 (1-1.9P + 0.9132) E, z modulus at zero porosity K = Ko(1-P) Where: K0 = Thermal conductivity @ zero porosity Thermal Expansion 8—6 °F 500 1000 1500 2000 2500 High-purity silicon nitride (Fine grain) 80 High-purity silicon nitride 400 E High-purity SiC \ Sialon 116 \\ .. 30 Silicon nitride (reaction bonded) 100 Glass ceramic J 10 Low-density SiC _1_ U‘ 0 per x 103 [O O C) Tensile strength (MPa) 03 o o 9?. O 0 200 400 600 800 1000 1200 1400 1600 Temperature (°C) W Effect of temperature on the strength of various engineering ceramics. Note that much of the strength is maintained at high temperatures. -—-—..._._—_—_____________—___________m_ Glass A super cooled liquid (no crystals) Beads produced about 2000 BC Glass blowing about 200 BC Only silica (glass former) until late 1600’s Various Properties 8-8 TABLE 8.3 Properties of Various Glasses ____H__________________.____———-———-—~———- Soda-lime Lead Borosilicate 96 Percent Fused glass glass glass silica silica ____________________...__"——————————-—-—-———-— Density High Highest Medium Low Lowest Strength Low Low Moderate High Highest Resistance to thermal Low Low Good Better Best sh0ck Electrical resistivity Moderate Best Good Good Good Hot workability Good Best Fair Poor Poorest Heat treatability Good Good Poor None None Chemical resistance Poor Fair Good Better Best impact-abrasion Fair Poor Good Good Best resistance Ultraviolet-light Poor Poor Fair Good Good transmission Relative cost Lowest Low Medium High Highest ___________,,_______.__.__....______————-——————-——- Glass, Mechanical Properties E = 55 to 90 GPa (8 to 13 million psi) Hardness = 5 to 7 mohs scale Theoretical strength = 35 GPa (5 million psi) Drawn Fibers = 2 GPa (300 Ksi) (stronger than steel) Static Fatigue 3 1/3 short-term loading Glass Ceramics Contain oxides, crystalline Hardness = 520 to 650 HK Thermal Expansion 2 0 Heat treatment for recrystallization 8-11 Graphite Crystalline form of carbon Strength and stiffness increases with temp. Common Applications: Fibers in composites and plastics Lubrication Nuclear components “Lead” pencils Electrodes for EDM Processing Molding Forming Machining 8-12 Diamond Crystalline form of carbon covalently bonded Hardest substance, 7000 to 8000 HK Synthetic (industrial) Diamond First made in 1955 Pressure (2 million psi) + Heat (5400°F) Low impurities “Gem” Quality Synthetic Higher electrical conductivity (50X natural diamond) Higher resistance to laser damage (10x natural diamond) Summary Table 8.1 8-13 h— : SUMMAR FL TABLE 8.1 TYPES AND GENERAL CHARACTERISTICS OF CERAMICS TYPE GENERAL CHARACTERISTICS Oxide ceramics Alumina Zirconia Carbides Tungsten carbide Titanium carbide Silicon carbide Nitrides Cubic boron nitride Titanium nitride Silicon nitride Sialon Cermets Silica Glasses Glass ceramics Graphite Diamond High hardness, moderate strength; most widely used ceramic; cutting tools, abrasives, electrical and thermal insulation. High strength and toughness; thermal expansion close to cast iron; suitable for heat engine components. Hardness, strength, and wear resistance depend on cobalt binder content; commonly used for dies and cutting tools. Not as tough as tungsten carbide; has nickel and molybdenum as the binder; used as cutting tools. High-temperature strength and wear resistance; used for heat engines and as abrasives. Second hardest substance known, after diamond; used as abrasives and cutting tools. Used as coatings because of low frictional characteristics; gold in color. High resistance to creep and thermal shock; used in heat engines. Consists of silicon nitrides and other oxides and carbides; used as cutting tools. Consist of oxides. carbides, and nitrides; high temperature applications. High temperature resistance; quartz exhibits piezoelectric effect; silicates. containing various oxides, are used in high—temperature nonstructural applications. Contain at least 50 percent silica; amorphous structures; several types available with a range of mechanical and physical properties. Have a high crystalline component to their structure; good thermal- shock resistance and strong. Crystalline form of carbon; high electrical and thermal conductivity, good thermal-shock resistance. Hardest substance known; avaiiable as single crystal or polycrystalline form; used as cutting tools and abrasives and as dies for fine wire drawing. _______—._.—..._........_._._..———————-———————--——— 8-14 ...
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chapter8 - CHAPTER 8 CERAMICS, GRAPHITE, AND DIAMOND:...

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