ch30.1-S10 - MY2100 Ch 3, Part 1, Slide 1 Chapter 3:...

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Unformatted text preview: MY2100 Ch 3, Part 1, Slide 1 Chapter 3: Structure of Metals and Ceramics structure processing properties Performance Well now look at the structure of solid materials at the level of arrangements of groups of atoms; that is, crystalline materials. MY2100 Ch 3, Part 1, Slide 2 How do metallic atoms assemble into solid structures? Why do crystalline solids form rather than noncrystalline solids? 1 Issues to Address ... How does the density of a metal depend on its structure? How efficient are the atoms packed in a unit cell? MY2100 Ch 3, Part 1, Slide 3 What is crystalline? A crystalline material is one in which the atoms or molecules are arranged in a regular pattern, in 3 dimensions. Example: NaCl, from last chapter: A non-crystalline material does not have this long-range order in its atomic arrangement. Noncrystalline SiO 2 - window glass MY2100 Ch 3, Part 1, Slide 4 2 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 of atoms Non dense, random packing Dense, regular packing MY2100 Ch 3, Part 1, Slide 5 3 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 (of which only 3 are of interest to us) ... Metallic Crystal Structures MY2100 Ch 3, Part 1, Slide 6 4 Rare due to poor packing (only Po has this structure) Close-packed directions are cube edges....
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ch30.1-S10 - MY2100 Ch 3, Part 1, Slide 1 Chapter 3:...

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