Material Science

Material Science - Chapter 3: The Structure of Crystalline...

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1 Chapter 3 - 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? Chapter 3: The Structure of Crystalline Solids
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2 Chapter 3 - • atoms pack in periodic, 3D arrays Crystalline materials. .. -metals -many ceramics -some polymers • atoms have no periodic packing Noncrystalline materials. .. -complex structures -rapid cooling crystalline SiO 2 noncrystalline SiO 2 " Amorphous " = Noncrystalline Modern classification Si Oxygen • typical of: • occurs for:
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3 Chapter 3 - Let’s begin with metals - Typically, only one element is present, so all atomic radii are the same. - Metallic bonding is not directional. - Electron cloud shields cores from each other
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4 Chapter 3 - • Non dense, random packing • Dense, ordered packing Energy and Packing Energy r typical neighbor bond length typical neighbor bond energy Energy r typical neighbor bond length
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5 Chapter 3 - Metallic Crystal Structures • How can we stack metal atoms to minimize empty space? 2-dimensions vs. Now stack these 2-D layers to make 3-D structures
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6 Chapter 3 - • Rare due to low packing density (only Po has this structure) Close-packed directions are cube edges.
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This note was uploaded on 11/03/2009 for the course PHYS 351 taught by Professor Staff during the Spring '08 term at UNC.

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Material Science - Chapter 3: The Structure of Crystalline...

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