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5b ,, f) ) — ENGR 220 Midterm Exam #2 Name: Alex ome Recitation Section #: {4 /0 } Spring 2012 DrexelOne ID (abc123):_a/ You will have 50 minutes for this exam. It isa closed-book and closed-note exam. You may not use a calculator or any other resources for this exam. Useful formulae, constants and a periodic table are provided on the last page. 1. (6 pts.) Three point defects that we discussed in class were ne only three): oO Cations 0 Grain boundaries Ol Edge Atoms Interstitials CO Proximity atoms of substitutional atoms Tetrahedra 1 Anions co Burger’s atoms Vacancies 2. (2 pts.) Choose one of your answers from above and briefly describe the point defect below (must be an actual point defect to earn credit): Vecantied fe wht there 15 on ery ty ie dt vbue = are Movin ly be on tom hich Cones Fhe plones lo Sag vito the tency = 1x (2 pts.) What is the name of the type of equation that is used to describe many thermally activated process? Abies ty vect ion Lg vel von Fen, Archentus -LF (2 pts.) Write an example of a specific equation we've discussed in class that is of the type described in question 3: eupg <2 Ru ‘(3 pts.) Linear defects have a large impact on which of the following bulk properties? or Density Ductility CO Elastic Modulus of Melting Temperature strength - 4 é (4 pts.) Below are two schematics of linear defects. Label each with the correct two word description. St few ‘isle cai dislocecttan ~ \ 7. (2 pts.) In which of the following metallic crystal structures can the defects in question 6 move most easily (choose one)? A FCC of Bcc oO HCP asc © Diamond Cubic es “uo _\ 8. (3 pts.) Which of the following microscopy techniques could be used to observe individual atoms? (choose all that are applicable) wo Transmission electron microscopy dontichy snicroscopy Scanning probe microscopy . alos are wach smaller tran the wavelength of vis vole yr = Lye (2 pts.) What chemical process is used to enhance the observation of grain boundaries in optical tnicroscopy? et 4 10. (1 pt. each - 6 pts. total) The following questions are in regards to diffusion: a. Alower temperature leads to higher) ep(circle one) diffusion coefficient. b. A lower activation energy leads tofhigheslower (circle one) diffusion coefficient. c. Having a small diffusing species in an open structure leads toffow)high (circle one) activation energy? d. Having a large diffusing species in a close-packed structure leads to low fig)Kcircle one) activation energy? e. Interstitial diffusion is slowerfaste} (circle one) than vacancy diffusion. -\ Z Justify your answer for 10(e): Labersfoyed radual tial — edoms — have nr €asee — fime monn Wrsre are wrore _— . scherstittes abu 11. (2 pts.) Anions are generally smallflargerXcircle one) than cations? shes + isterstitial 5 \A he oreney bk move iato . far ere much serail Velanty lors $0 
