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第�,�� - Introductory Materials...

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Unformatted text preview: Introductory Materials Science and Engineering 1 MLE 1101 Fall 2008 Tutorial III C02(E3-06-07); D06(E1-06-04); A03(E3-06-07) Office hour: 4:30-5:30 pm on Tuesdays, E4-8-11 Assistant Professor Gengchiau Liang [email protected] Note: Solution will be provided on my website after class (http://www.ece.nus.edu.sg/stfpage/elelg/ ) Introductory Materials Science and Engineering 2 Tutorial 3 (Ch4) 1. Calculate the number of vacancies per cubic meter in gold at 900 ° C. The energy for vacancy formation is 0.98 eV/atom. Furthermore, the density and atomic weight for Au are 19.32 g/cm 3 and 196.9 g/mol, respectively. ANS: CH4/P.83 Determination of the number of vacancies per cubic meter in gold at 900 ° C (1173K) requires the utilization of Equations (4.1) and (4.2) (as shown in text book) as follows: = 3.65 × 10 18 cm-3 = 3.65 × 10 24 m-3 Introductory Materials Science and Engineering 3 POINT DEFECTS • Vacancies : vacant atomic sites in a structure. Vacancy distortion of planes • Self-Interstitials :-"extra" atoms positioned between atomic si self- interstitial distortion of planes Note: The formation of this defect is not highly probable. The concentration of this defect is much lower than the one of vacancies. Introductory Materials Science and Engineering 4 Boltzmann's constant (1.38 x 10-23 J/atom-K) (8.62 x 10-5 eV/atom-K) No. of defects No. of potential defect sites. Activation energy Temperature Each lattice site is a potential vacancy site • Equilibrium concentration varies with temperature! Equilibrium Concentration: Point Defects ⎜ N v N = exp − Q v k T ⎛ ⎝ ⎜ ⎞ ⎠ Introductory Materials Science and Engineering 5 Introductory Materials Science and Engineering Two outcomes if impurity (B) added to host (A): • Solid solution of B in A (i.e., random dist. of point defects) OR Substitutional alloy (e.g., Cu in Ni ) Interstitial alloy (e.g., C in Fe ) POINT DEFECTS IN ALLOYS Introductory Materials Science and Engineering 6 Introductory Materials Science and Engineering IMPURITIES IN SOLIDS Several influencing factors: 1. Atomic size factor: < 2. Crystal structure: same 3. Electronegativity: comparable 4. Valences: similar % 15 ± Substitutional type Cu and Ni: 1 : 0.128nm vs. 0.125nm; 2 : Both FCC; 3 : 1.9 vs. 1.8; 4 : 1 vs. 2 Introductory Materials Science and Engineering 7 Tutorial 3 (Ch4) ANS: CH4/P.84 2. Below, atomic radius, crystal structure, electronegativity, and the most common valence are tabulated, for several elements; for those that are nonmetals, only atomic radii are indicated. hich of these elements would you expect to form the following with copper: a. A substitutional solid solution b. An interstitial solid solution For complete substitutional solubility the following criteria must be met: 1) the difference in atomic radii etween Cu and the other element ( Δ R% ) must be less than ± 15%, 2) the crystal structures must be the same, ) the electronegativities must be similar, and 4) the alences should be the same, or nearly the same...
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第�,�� - Introductory Materials...

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