lect8-review

lect8-review - Lecture 8: Biomaterials Review For Exam...

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Lecture 8: Biomaterials Review For Exam BIOMATERIALS The application And motivation Where we begin structure (order) they all influence each other properties processing Start with crystals. Both METALS and CERAMICS form  crystals.  In fact, all metals, except in special cases  involving very careful processing, are CRYSTALLINE. METALLIC BONDING: nuclei with free electrons Spheres pack as closely as possible so electrons can roam FCC structure: 1
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This structure is the most closely packed that the spheres  can be.  There are three layers. (A, B, C)  The ABC layering structure is the Face Centered Cubic  Structure. (FCC).  An identical level of close packing would be to have the  third layer over the first layer. (A, B, A layering) This is the hexagonal close packed structure 2
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There are two important interstitial sites (sites between  the atoms) that are worth noting in these structure. 1. Tetrahedral sites 2. Octahedral sites Tetrahedral sites are at the middle of 4 SPHERES. Octahedral sites involve 6 SPHERES—THREE up and  THREE down. (They make an octahedron) 3
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(image from wikipedia) Hexagonal close packed (the sister structure to FCC) A B A BIOMATERIALS which are CERAMICS: CaO, Al 2 O 3 , TiO 2 Ceramics are defined (by ceramists) as  INORGANIC, NONMETALIC materials CERAMICS typically have positively and negatively  charged atoms (TiO 2 ) Ti 4+  and O 2- CRYSTALS of CERAMICS are arrange so atoms can be 4
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As close as possible Highly shielded from those of the same charge PAULING’S RULES are a simple set of empirical rules  to determine where the positive and negative atoms sit in  the crystal structure.  The LARGER ATOMS tend to sit on the ATOMIC  SITES. The SMALLER ATOMS sit in the  INTERSTITIAL SITES. There are two important interstitial sites (sites between  the atoms) that are worth noting in these structure. 3. Tetrahedral sites 4. Octahedral sites Tetrahedral sites are at the middle of 4 SPHERES. (One up, three down or three up, one down) Octahedral sites involve 6 SPHERES—THREE up and  THREE down. (They make an octahedron) 5
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Where are the interstitial sites in the structures we have  considered? FCC. .. The tetrahedral sites sit between each corner atom and the  three nearest face atoms. There are 8 corner atoms per unit cell and 1 tet. Site per  corner so there are 8 tet. Sites per unit cell. (and 4 atoms  per unit cell as we calculated in lecture 2.) That means  there are 2 tet sites per atom in the FCC structure. Where are the OCTAHEDRAL SITES?
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This note was uploaded on 09/24/2009 for the course BENG 434 taught by Professor Erinlavik during the Fall '08 term at Yale.

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lect8-review - Lecture 8: Biomaterials Review For Exam...

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