Physical metallurgy (Muda Ibrahim)

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Physical metallurgy (Muda Ibrahim)

  1. 1. 1.0) PHYSICAL METALLURGY <ul><li>LECTURE OUTLINE: </li></ul><ul><li>Primary Bonding (atomic bonding). </li></ul><ul><li>Define crystal lattice. </li></ul><ul><li>Define the methods for measuring distance between atom through .(Assignment 2) </li></ul><ul><li>Disfigurement in crystal structure. </li></ul>
  2. 2. Primary Bonding <ul><li>Ionic </li></ul><ul><li>Covalent </li></ul><ul><li>Metallic </li></ul><ul><li>Bonding involves the valence electrons. </li></ul><ul><li>Bonding occurs due to the tendency of the atoms to assume stable electron structures (completely filled outer shells) </li></ul>
  3. 3. Ionic Bonding • Occurs between + and - ions. • Requires electron transfer. • Large difference in electronegativity required. • Example: NaCl Na (metal) unstable Cl (nonmetal) unstable electron + - Coulombic Attraction Na (cation) stable Cl (anion) stable
  4. 4. Examples: Ionic Bonding • Predominant bonding in Ceramics Adapted from Fig. 2.7, Callister & Rethwisch 3e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond , 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. Give up electrons Acquire electrons NaCl MgO CaF 2 CsCl
  5. 5. c02f09
  6. 6. Covalent Bonding C: has 4 valence e - , needs 4 more H: has 1 valence e - , needs 1 more Electronegativities are comparable. <ul><li>similar electronegativity  share electrons </li></ul><ul><li>bonds determined by valence – s & p orbitals dominate bonding </li></ul><ul><li>Example: polymers , GaAs, InSb, SiC, CH 4 </li></ul>shared electrons from carbon atom shared electrons from hydrogen atoms H H H H C CH 4
  7. 7. c02f11 Metallic Bonding <ul><li>Metallic bonds have up to 3 valence electrons that are not bound to a specific atom. </li></ul><ul><li>They drift throughout the metal forming a “sea of electrons” or “electron cloud”. </li></ul><ul><li>The nonvalence electrons and nuclei for the “ion cores”. </li></ul><ul><li>The free electrons act as a “glue” to hold the ion cores together. </li></ul><ul><li>These are good conductors of heat and charge (electricity). </li></ul>
  8. 8. Secondary Bonding ( van der Waals ) <ul><li>Interaction between dipoles; dipoles are a separation of charge (+/-). </li></ul><ul><li>Weaker forces ( 10kJ/mol ) than primary bonding, yet these bonds still influence physical properties. </li></ul><ul><li>Secondary bonding exists in virtually all atoms and molecules, but their presence may be obscured by primary bonding. </li></ul>
  9. 9. SECONDARY BONDING • Permanent dipoles -molecule induced • Fluctuating dipoles -general case: -ex: liquid HCl -ex: polymer secondary bonding secondary bonding secondary bonding asymmetric electron clouds + - + - secondary bonding H H H H H 2 H 2 secondary bonding ex: liquid H 2 H Cl H Cl + - + - secondary bonding
  10. 10. Summary: Bonding Type Ionic Coulombic force Covalent Metallic Secondary Van der Waals Bond Energy Large Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury smallest Comments Nondirectional ( ceramics ) Directional ( semiconductors , ceramics polymer chains) Nondirectional ( metals ) Directional inter-chain ( polymer ) inter-molecular
  11. 11. Summary: Primary Bonds Ceramics (Ionic & covalent bonding): Large bond energy large T m large E small  Metals (Metallic bonding): Variable bond energy moderate T m moderate E moderate  Polymers (Covalent & Secondary): Directional Properties Secondary bonding dominates small T m small E large  secondary bonding
  12. 12. Crystal Structure
  13. 13. Crystal Structure
  14. 14. Crystal Structure
  15. 15. Crystal Structure
  16. 16. Crystal Structure
  17. 17. Crystal Structure
  18. 18. Crystal Structure
  19. 19. Crystal Structure
  20. 20. Disfigurement Crystal Structure
  21. 21. Edge Dislocation
  22. 22. Screw Dislocation
  23. 23. Screw Dislocation
  24. 24. Point Defect
  25. 25. <ul><li>Thank You </li></ul>

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