3 - Summary (Chapter 1-2) Materials Science and Engineering...

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Performance Summary Summary ( ( Chapter Chapter 1 1 - - 2) 2) Materials Science and Engineering Materials Science and Engineering Material science is the investigation of the relationship among processing, structure, properties, and performance of materials.
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Atomic Bonding Atomic Bonding
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Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): s ec on dar y bon d in g Large bond energy large T m large E small a Variable bond energy moderate T m moderate E moderate a Directional Properties Secondary bonding dominates small T small E large a PRIMARY BONDS
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CHAPTER 3: CHAPTER 3: STRUCTURE OF STRUCTURE OF CRYSTALLINE SOLIDS CRYSTALLINE SOLIDS
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• atoms pack in periodic, 3D arrays • long-range order •t y p i c a l o f : -metals -many ceramics -some polymers • atoms have no periodic packing •o c c u r s f o r : -complex structures -rapid cooling Si Oxygen crystalline SiO crystalline SiO 2 noncrystalline SiO noncrystalline SiO 2 " Amorphous " = Noncrystalline Materials and packing: Types of solids
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Si (crystalline) SiO 2 (amorphous)
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• Non dense, random packing •D en s e , regular packing Dense, regular-packed structures tend to have lower energy. Energy r typical neighbor bond length typical neighbor bond energy Energy r typical neighbor bond length typical neighbor bond energy Energy and packing Energy and packing
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Atomic hard sphere model is used to describe the arrangement of atoms. Lattice: A 3D array of points in space coinciding with atom positions (or sphere centers). Hard sphere model and lattice:
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Unit cell: (Lattice cell) Smallest structural unit that decribes the whole crystal structure. Unit cell: Reduced sphere model:
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As an easy and simple way of representation we use cubes or similar geometrical tools to represent a unit cell.
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• 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.
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3 - Summary (Chapter 1-2) Materials Science and Engineering...

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