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Day 21: Ceramics. Inorganic & Nonmetallic. Compounds between metallic and non-metallic elements Traditional: Clay based bricks, tiles, china, porcelain, and glasses Engineering: High tech materials useful in high strength applications, take advantage of the unique properties.
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Day 21: Ceramics • Inorganic & Nonmetallic. Compounds between metallic and non-metallic elements • Traditional: Clay based bricks, tiles, china, porcelain, and glasses • Engineering: High tech materials useful in high strength applications, take advantage of the unique properties
Nature of Ceramics • Bonding is ionic and covalent mix. These are extremely strong bonds. This leads to high melting point, high strength and high modulus of elasticity. • Crystallinity is complex. Different sizes of atoms. Charge conservation. This makes slip, so common in metallic crystals, practically impossible. Also leads to less efficient packing, and lower density.
Good Properties • Strength and Hardness • High Temperature Resistance • Resistance to Corrosion • Low Density
Challenge • Brittleness. The problem is that these materials have ductility, fracture toughness, and great flaw sensitivity. • BUT, we know that it is possible to use brittle materials, provided that we do so in an intelligent way.
Why Use Ceramics for Structural Applications, I.E. Turbocharger Rotor? • High temperature resistance (hot exhaust gases) • Low coefficient of thermal expansion (small blade tip clearance) • Low mass (low polar moment of inertia for fast spin up) • Durability (survive over 100,000 miles) • Low cost (need willing purchasers)
http://global.kyocera.com/application/automotive/auto_engine/turbo.htmlhttp://global.kyocera.com/application/automotive/auto_engine/turbo.html
Table 1.1 Turbocharger Rotor Materials (data from Callister)
Figure 1.2 Comparison of wide-open throttle acceleration for ceramic and metal turbocharger rotors, 2.3 liter engine - Zephyr test vehicle. (Wachtman, 1989)
Overview of Advantages of Ceramics • temperature resistance • high hardness • low density • corrosion resistance
Special Design Considerations for Ceramics • brittleness • difficulty of manufacture.