Lecture3 - Chapter 3: The Structure of Crystalline Solids...

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Chapter 3 - 1 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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Chapter 3 - 2 Crystal structure polymer Cobalt ceramic crystal plate Microstructure of Ta2O5 bismuth methal
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Chapter 3 - 3 Non dense, random packing Dense, ordered packing Dense, ordered packed structures tend to have lower energies. Energy and Packing Energy r typical neighbor bond length typical neighbor bond energy Energy r typical neighbor bond length typical neighbor bond energy
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Chapter 3 - 4 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 Adapted from Fig. 3.22(b), Callister 7e. Adapted from Fig. 3.22(a), Callister 7e. Materials and Packing Si Oxygen typical of: occurs for:
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Chapter 3 - 5 Section 3.3 – Crystal Systems 7 crystal systems Fig. 3.4, Callister 7e. Unit cell: smallest repetitive volume which contains the complete lattice pattern of a crystal. a, b, and c are the lattice constants
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Chapter 3 - 6 Unit Cell Example: 2D honeycomb net can be represented by translation of two adjacent atoms that form a unit cell for this 2D crystalline structure
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Chapter 3 - 7 Tend to be densely packed. 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. - Electron cloud shields cores from each other Have the simplest crystal structures. We will examine three such structures. .. Metallic Crystal Structures
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Chapter 3 - 8 Rare due to low packing denisty (only Po has this structure) Close-packed directions are cube edges.
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This note was uploaded on 11/25/2008 for the course MATSCI 104 taught by Professor Lan during the Spring '08 term at UCLA.

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Lecture3 - Chapter 3: The Structure of Crystalline Solids...

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