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09-18-Lecture

09-18-Lecture - 1 SOLIDS IMPER FECT IONS ENGR 213 DEFECTS...

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Unformatted text preview: 1 SOLIDS IMPER FECT IONS ENGR 213 DEFECTS ➜ no perfect crystals ➜ all have defects = lattice irregularity ➤ point defects 0.1nm ➤ line defects (dislocations) 10nm ➤ interfacial / area defects 0.01 - 0.1 μ m ➤ volume defects 0.01 - 1mm POINT DEFECTS IN METALS ➜ Interstitial ➤ rare ➤ extra atom ➤ space is smaller than atom ➤ lowers stability of structure ➜ Vacancies ➤ Common ➤ “hole” in lattice POINT DEFECTS IN METALS Nobody’s home! Five’s a crowd! VACANCIES IN METALS ➜ exist due to 2nd law of thermodynamics ➜ @ equilibrium, the number of vacancies is given by ➜ Q v = energy to remove atom from lattice site by breaking bonds w/ nearest neighbors ➜ T = temperature in deg Kelvin ➜ k = Boltzmann’s constant (8.6E-5 eV/atom-K) kT Q v v Ne N-= POINT DEFECTS IN CERAMICS ➜ anions & cations ➤ vacancies & interstitials for each ion species ➤ anion interstitials rare due to size ➜ electroneutrality must be maintained ➤ charge balance of anions and cations ➤ stoichiometric ➜ Frenkel defect ➤ cation vacancy + cation interstitial ➤ Stoichiometric ➜ Schottky defect ➤ cation vacancy + anion vacancy ➤ stoichiometric TWO POINT DEFECTS IN CERAMICS Grass looks greener!...
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09-18-Lecture - 1 SOLIDS IMPER FECT IONS ENGR 213 DEFECTS...

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