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ss_quiz_1 - 13—344 Spring 2005 Name L— E Quiz 1 3 March...

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Unformatted text preview: 13—344 Spring 2005 Name: L—\ E% ' Quiz 1 3 March, 2005 ID#: Honor Pledge: Use the backs of the pages if you need more space. Clearly label any work there with an appropriate question number. 1. (20 points) "2, A. Draw a BCC unit cell. Using another diagram(s) to identify: '57 B. the(113)p1ar1e. 4,2,,“ 1,, C. the [113] direction 77 D. the (1, l, 3) position. Vs E. Suppose the material in question is BCC Vanadium (V) with a lattice parameter of Eta-T" hk _ . 0.3028 nm, estlmate the atomlc radius of a Watcm. \l BHABMM 4 F. The atomic weight of V is 50.94 g/mole. Use the unit-cell information above to estimate its density. I? {900 «Coon . _ - 1/3 a ’ ‘3— (”kl-3.1% 2) (20 points) The atomic number of silicon (Si) is 14. The energy levels for its 14 electrons are given in the table below. Energy (eV) A) Use the spdf notation to describe the electron configuration characteristic of a single (isolated) silicon atom. 1839 1 L 1 2. 149 \6 25} 2? 35 g? 99.5 2.9 3.1 B) Sketch a representation of a single (isolated) silicon atom using a planetary mod =- I? 1. Es. V C. Draw a well-labeled energy—l diagram characteristic of a single (isolated) _. 5115 W I“, \V Z 3‘ silicon atom. \‘A" W 'Z 5 new '\\. ' \s D. A piece of solid silicon containing ~1023 atoms is a good semiconductor. Sketch a well— labeled energy-band diagram representative of solid silicon (where the atoms are now no longer isolated). E: O Vet/WW C?) Ea 2%xm-‘D W57 (W‘s LE?H\‘\N page”. ////////, Fuflh \fi'; 3) (20 points) (A) The Viscosity of a “3740 silica-based glass (like Pyrex) is 1011 Pa—s at 650 °C and 10‘5 Pa—s at 1000 0C. Using an Arrhenius model for the temperature-dependent viscosity, calculate the temperature at the glass softening point where the viscosity is 106'6 Pa-s. Clearly show your work. (k=8.61?x10‘5 eV/K; 1ov=1.6x10-19J; st.3144J/mo1o-t<). (B) Sketch qualitatively - exact numbers are not required — the variation of viscosity as a a function of temperature. g (C) Fused silica (pure SiOz) softens at approximately 1500 °C whereas 7740 glass softens at a much lower temperature. Briefly explain what is responsible for the difference. ‘ ® “LUV"owWw—V 2%} @‘N‘v J» ,, 4r ESL. ‘7’?” 2M WL Geological. qt“:\ "5 gm U065 :- th’lb + E: ' k%.b\\“5€% (035% T Nov- Woe-‘4: WM web-“MS 1/ \W m wow?“ 05- mm 6‘ Pawn? q/\ 9‘- WW “M M?" mm M; ”1X1“ 4.- (20 points) H C1 (A) The monomer unit for poly(viny1 chloride) [PVC] 3 given in the | I adjacent diagram. If the average molecular weight of a sample of PVC is 38,100 g/mole, what is the degree of polymerization of the ~ C - C - average PVC molecule? l l Atomic wgts in gfmole: H 1; C 12; C1355 “3“:- Ben 2m, msss- H H n : e2: b9: 3%“??? :_ b\D 62.5’ ---— 1.00.ng S? vs 'Wr. (B) Do all PVC molecules in this sample have this degree of polymerization? W m WLuV-‘F \HX Briefly justify your answer. ’2, bo\LL. ‘ ,3 = : I k ‘7‘ 1M EV) 7) m mu 0% bmu M k may. EV. ‘Nus \s is W“ 0? ‘Nr. memes. (C) Draw a sketch illustrating the conformation of a typical PVC molecule in this sample. '2’. 79 (D) The glass transition temperature of PVC is 87 0‘C. Suppose you were to compare the viscosity of two sample of PVC at 140 °C where one sample has an average MW of 2500 glinole and the other has an average MW of 250,000 g/mole. Would these viscosities be the same 01' different? Briefly justify your answer. \QO. Wt. WW “by $097997. ku\\.\._ We at “firs-“Val. \lxswen‘wl ku. W N‘s-36$, Nude emu eczema, u' w W m We eenuaseaas. 2g Page - 4 In the following multiple-choice problems, circle the one answer which BEST completes the ' sentence. 3 points per problem. No partial credit. 5. Energy bands form in many-atom solids, because: some materials are metals and others are insulators; @atomic electron energy levels Split to satisfy the Pauli exclusion principle; / c. empty electron orbitals overlap with filled orbitals; d. secondary bonds change the nature of the primary bonds; e. none of the above. 6. Most metals have a high electrical conductivity, because: a) metal atoms are small and can move quickly in a solid; b) valence electrons in metals are tightly bound to the atomic nuclei; @he valence band is unfilled or partially filled; / d) the valence band is filled; 6) none of the above. 7. _ Metals and alloys can be shaped by: a) extrusion; b) rolling; c) casting; / d) stamping; ’31] of the above. 8. Cement: a) is a polymer; b) forms when water evaporates from a wet mixture of CaO and SiOg—based powders; @orms by a chemical reaction between water, CaO powder, and SiOz-based powder; / d) is a good electrical conductor; e) none of the above 9- The glass transition temperature of window glass is: a) the same as the melting temperature; b) greater than the melting temperature; ove room temperature; / below room temperature; e) none of the above. ‘ Paoe— ‘fi 10. A thermoplastic polymer: a. melts or softens when heated; b. becomes brittle if cooled below its glass transition temperature; c. does not involve covalent crosslinks; d. may be amorphous, semicrystalline, or crystalline, depending on the polymer; .all of the above. 11. A thermoset polymer: ® has strong primary bonds linking different molecules or different parts of the same molecule; b. can be recycled; / c. is formed by lightly crosslinking thermoplastic polymers like poly(ethylene); d. is a silicon-based polymer; e. none of the above. 12. A key difference between a thermOplastic polymer and an elastomeric material like rubber is: @ rubber has a small number of covalent crosslinks and thermoplastic polymers have none; b. thermoplastics don’t melt when heated but rubbers do; /» c. rubber can be snbj ected to extensive plastic deformation whereas typical thermoplastics have little plasticity; d. all of the above; 6. none of the above. 13. Ceramic materials are often made by sintering of compacted powder, because a) ceramics melt at very high temperatures; _ b) ceramics are generally too, brittle to form by deformation processing like most metals can be; / c) ceramics usually involve ionic-covalent bonding; . @ll of the above; e) aand c. 14. One important difference between an amorphous material and a crystalline material is that amorphous materials a. are transparent whereas crystalline materials are not; b. have long ranged translational order whereas crystalline materials do not ; @iave a structure like a liquid wheras crystalline materials have translational order; if d. are easy to create whereas crystalline materials are difficult to create ; ,/ e. none of the above. Pace u 6 ...
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