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ch03-Structure of metals and ceramics

ch03-Structure of metals and ceramics - Chapter 3...

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Chapter 3 - Chapter 3: Structures of Metals & Ceramics X-ray diffraction photograph X-ray diffraction in metals This notes have been prepared by Jorge Seminario using the textbook material and the extraordinary effort of CHEN 313 Materials students (Spring- 2009) Ashley Brzenk, Samantha Burrows, and Jason Calobrisi
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3.1 Introduction Material to be Covered: o Arrangements of atoms in the solid state o Crystalline Solids-Unit Cells o Crystallographic points, directions, and planes o Single Crystals  o Polycrystalline materials o Noncrystalline Materials http://www.crystallinepeaceproject.org/Images/CrystallineGroup2.jpg http://www.ganoksin.com/borisat/nenam/nenamart/rw-clipart/rw11-sun49.jpg
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http://www.hgms.org/FacetedGems-rotated.jpg
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http://www.idfuel.com/images/012705_TTamorphous_image.gif http://members.wri.com/jeffb/visualization/lattice.jpg 3.2 Fundamental Concepts Crystalline-atoms  position in a repetitive  3D pattern Non crystalline  (amorphous)-atomic  order is absent Lattice- a 3D array of  points coinciding with  atom positions or sphere  centers
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Chapter 3 - 5 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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http://upload.wikimedia.org/wikipedia/commons/0/0c/Fluorite-unit-cell-3D.png 3.3 Unit Cells Small repeating  patterns used to  subdivide a crystal  structure Basic structural unit or  building block of the  crystal structure Defines the crystal  structure by virtue of  its geometry and the  atom positions within
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Chapter 3 - 7 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
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FCC- Face-Centered Cubic a=2R 2 n=4 APF=0.74 Coordination #= 12 ex. copper, aluminum, silver, and gold BCC- Body-Centered Cubic a=4R/ 3 n=2 APF=0.68 Coordination #=8 ex. chromium, iron, and tungsten HCP- Hexagonal Close-Packed a=2R c/a=1.663 n=6 APF=0.74 Coordination #= 12 ex. cadmium, magnesium, titanium, and zinc a= cube length (short side  in HCP) c=long side length in HCP R= atomic Radius n=# of atoms per unit cell -------------------------------- APF- the  volume fraction of   the unit cell occupied by  atoms Coordination #- number of  atoms touching every atom  in a unit cell ALL IMAGES ON THIS PAGE FROM: http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/CrystalStructure
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Chapter 3 - c03tf01 FCC = face-centered cubic HCP = hexagonal close-packed BCC = body-centered cubic 1 nm = 10 -9 m = 10 Ǻ
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Chapter 3 - 10 Rare due to low packing density (only Po has this structure) Close-packed directions are cube edges.
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