Crystalline Solids_Crystal Structure

Crystalline Solids_Crystal Structure - Materials Science...

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Unformatted text preview: Materials Science and Engineering MIME 1650 Lecture 3 1 6 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 7 Chapter 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 Materials Science and Engineering MIME 1650 Lecture 3 2 8 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 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: 9 Chapter 3 - Section 3.3 Crystal Systems 7 crystal systems 14 crystal lattices 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 Materials Science and Engineering MIME 1650 Lecture 3 3 10 Chapter 3 - 7 crystal systems a b c Triclinic = = 90 o a b c Monoclinic = = = 90 o a b c Orthorhombic = = 90 o a = b = c Rhombohedral = = = 90 o a = b c Tetragonal = = 90 o , = 120 o a = b c Hexagonal = = = 90 o a = b = c Cubic Unit cell Interaxial angles Axial relationships Crystal system 11 Chapter 3 - Section 3.4 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 Materials Science and Engineering MIME 1650 Lecture 3 4 12 Chapter 3 - Tend to be densely packed....
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Crystalline Solids_Crystal Structure - Materials Science...

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