Download ENGR 3450, Spring 2012 - Test 1: Metals Crystal Structures and Properties - Prof. Peter Co and more Exams Engineering in PDF only on Docsity!
Name: 100 Points – February 27h, 2012 Instructions: Please read every question carefully. You may use calculators, but all other material is to be off of the table (including all cell phones). Write clearly. If you need to, you may use the back of the sheet for your solutions. Remember to only use relevant information provided in the question. PROBLEM #1 (15 points): Fill in the below table for metals (10 points) Crystal structure Atomic packing fraction Coordination number Close packed direction length Atoms per unit cell 2R = a 1 Body centered cubic
4R=√2a 4 Hexagonal Close Packed 0.74 12 2R=a For the two shaded boxes, show your work on how you arrived at the answer. (4 points) For the box outlined in bold , for the number you gave, draw the unit cell you chose. (1 point) PROBLEM #2 (10 points): (a) Draw clearly the diamond (a.k.a. the Zinc Sulfide) structure. Neatness counts. (3 points) (b) For a carbon atom ( effective radius of carbon in the diamond cubic structure is 0.077nm). Calculate the lattice parameter. (4 points) (c) Calculate the atomic packing factor. (3 points)
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Name: 100 Points – February 27h, 2012 PROBLEM #3 (6 points): Bohr’s model describes a fixed energy level for each orbital. Is this what is predicted by the wave mechanical model? Please explain why or why not. PROBLEM #4 (24 points): You have eight materials: HF, Si, TiO 2 , AgAu, GeC, W, Fe 2 O 3 and NaCl. (a) Tell which type of bond these materials are expected to exhibit (8 points) (b) For those compounds whose bonds you expect to exhibit any ionic character, please rank the degree of ionicity (8 points) (c) Classify the materials as: likely to form either a close packed metallic structure, or a tetrahedrally coordinated structure, or a crystal whose structure is governed by radius ratio rules. (8 points)
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Name: 100 Points – February 27h, 2012 PROBLEM #7 (11 points): (a) List the four molecular chain structures of polymers and show their trend of increasing mechanical strength. (4 points). (b) What helps to lead to amorphous polymeric materials? Provide three explanations, using one explanation involving chemical modification, one involving variations in chain configurations, and one involving processing (3 points). (c) Polymeric material exhibit defects. Please draw and identify at least 4 defects. (4 points) PROBLEM #8 (6 points): Determine the number of equivalent directions/planes for the following systems. Name the equivalent directions/planes. Orthorhombic: {112} Tetragonal: <100>
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Name: 100 Points – February 27h, 2012 PROBLEM #9 (8 points): Draw the following features in the appropriate unit cells. Insert all lattice parameters. (a)
^11 23
in hexagonal (a=b≠c; ==°,=120°) (2 points). (b)
^10 1 0
in hexagonal (a=b≠c; ==°,=120°) (2 points). (c) [301] in cubic (a=b=c; ===°) (2 points). (d)
^1 3 2
in cubic (a=b=c; ===°) (2 points).
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Name: 100 Points – February 27h, 2012 Bonus #1 (5 points): Calculate the APF for the hexagonal close packed structure. Bonus #2 (5 points): There is a phenomenon called “grain boundary poisoning”, where the properties associated with the grain boundaries are significantly degraded by the presence of a second species. Two common examples are: (1) mercury penetrates into aluminum and the mercury atoms sit on the grain boundary, and (2) bismuth will find copper grain boundaries, and will preferentially occupy sites along copper grain boundaries. Why would this phenomenon occur? Bonus #3 (5 points): Write the Burger’s vector for a dislocation in fcc Al (a 0 = 0.405nm) and for a dislocation in bcc Fe (A 0 = 0.287nm), including the magnitude of the Burger’s vector.
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