chp3 - CHAPTER 3: CRYSTAL STRUCTURES & PROPERTIES...

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1 Chapter 3- Slides adapted from J Wiley material ISSUES TO ADDRESS. .. • How do atoms assemble into solid structures? (for now, focus on metals) • How does the density of a material depend on its structure? • When do material properties vary with the sample (i.e., part) orientation? 1 CHAPTER 3: CRYSTAL Chapter 3- Slides adapted from J Wiley material 2 • Non dense, random packing • Dense, regular packing Dense, regular-packed structures tend to have lower energy. ENERGY AND PACKING
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2 Chapter 3- Slides adapted from J Wiley material • atoms pack in periodic, 3D arrays • typical of: 3 Crystalline materials. .. -metals -many ceramics -some polymers • atoms have no periodic packing • occurs for: Noncrystalline materials. .. -complex structures -rapid cooling crystalline SiO 2 noncrystalline SiO 2 " Amorphous " = Noncrystalline Adapted from Fig. 3.18(b), Callister 6e. Adapted from Fig. 3.18(a), MATERIALS AND PACKING Chapter 3- Slides adapted from J Wiley material What type of packing would provide a larger elastic modulus? 1. amorphous 2. crystalline
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3 Chapter 3- Slides adapted from J Wiley material 4 • tend to be densely packed. • have several reasons for dense packing: -Typically, only one element is present, so all atomic radii are the same. -Metallic bonding is not directional. -Nearest neighbor distances tend to be small in order to lower bond energy. • have the simplest crystal structures. We will look at four such structures. .. METALLIC CRYSTALS Chapter 3- Slides adapted from J Wiley material 5 • Rare due to poor packing (only Po has this structure) Close-packed directions are cube edges. Coordination # = 6 (# nearest neighbors) (Courtesy P.M. Anderson) SIMPLE CUBIC STRUCTURE (SC)
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4 Chapter 3- Slides adapted from J Wiley material 6 • APF for a simple cubic structure = 0.52 Adapted from Fig. 3.19, Callister 6e. ATOMIC PACKING FACTOR Chapter 3- Slides adapted from J Wiley material • Coordination # = 8 7 Adapted from Fig. 3.2, (Courtesy P.M. Anderson)
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This note was uploaded on 04/09/2008 for the course MSE 205 taught by Professor Anderson during the Spring '08 term at Ohio State.

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chp3 - CHAPTER 3: CRYSTAL STRUCTURES & PROPERTIES...

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