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t4f04 - MAT 200 Quiz#4 Fall 2004 circle Name(Print...

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Unformatted text preview: MAT 200 Quiz #4 - Fall 2004 circle Name (Print) _ Professor JK ID Number Professor Hare This is a closed book test. No notes, books, or information stored in calculator memories may be used. Cheating will be punished severely. All of your work must be written on these pages and turned in. To receive fill or partial credit on problems, you must show your step-by-step calculations starting with the relevant equations. Units must be shown and all plots must have labeled axes. Sketches must be clear and well labeled, and your writing must be legible. Be sure that you read and answer all parts of each question. Equations and constants R = 1.987 cah’mol-K NAvg = 6.023 x 102 atoms/moi Multiple choice questions are 2 points each: . Covalently bonded ceramics tend to have a relatively low packing fractional density because a. the atoms involved are Ii ght elements ' b. the coordination of the atoms is high, 6 or more c. the coordination of the atoms is low, 3 or 4 d. the bonds are weak . The principal test method for estimating the strength of a ceramic is the a. impact test ' b. tensile test c. flexural test d. a large stress/strain ratio . The coordination of the cation in an ionic ceramic structure depends on a. the density b. the charges on the ions 0. the ratio of the cation to anion radii d. none of the above Porous ceramics are generally useful as a. high strength materials b. high ductility materials 0. thermal insulators d. all of the above -pasel- C 1.1... I An elastomer can be made stiffer (the modulus can be increased) by a. heating it to above the Tg b.‘ increasing the mount of- eressnlinking- c. decreasing the ambunt of cross- dinkingg d none of the above Ductility is observed in polymers when a. dislocations move easily b. covalent bends are broken:- ‘ c. the temperature is below T g (1. molecules can slide past one another Thermoplastic polymers differ from thermosetting polymers m that a. they cannot be crystalline b.- they are net. recyclable c. they have a linear molecular structure (as opposed to cross—linked or network structure) d all of the above Which is one of the criteria for a polymer to behave as an elastorner: a the molecules are coiled b. the molecules should be cross—linked _ c. the Tg must be below room temperature d. all of the above The mechanical property which' is signflcantly. better (than a normal ceramic) in a ceramic- ceramic composite such as two—phase zirconia is a.- yield strength b. hardness c. elastic modulus d. fracture toughness K10 The composite property which can always be calculated exactly using the law of mixtures is: a: ' ' b. tensile strength c. elastic modulus d. thermal conductivity 7 _._ A fliennoplashc most likely to crystalhze would he a. branched and atactic b. branched and isotactic c. not branched and isotactic d. not branched and atactic The tensile strength of a polymer will be increased by a. increasing the average molecular weight b. decreasing the amount of crystallinity c. decreasing the degree of polymerization d. none of the above A high strength lightweight composite suitable for use at very high temperatures is: a. fiberglass in a polyethylene matrix b. disPersion strengthened aluminum 0. carbon—carbon d. graphite ‘fiberih a polymer matrix ' - Page 2 - ' $ 14. Glass fiber is much stronger than bulk glass because a the atoms are covalently rather than ionically bonded b fiber is ductile and ‘0qu glass is brittle c the individual Si—O bonds are stronger in the fiber (1 the surfaces are free of defects such as flaws and cracks . Polymer fiber is much stronger than the bulk polymer because a the molecules in the fiber are bonded more strongly together with increased Van der Waals attraction b the fiber is denser c the molecules are oriented in the fiber direction and strong covalent bonds support the load d the degree of polymerization in the bulk is much higher 16. (5 points) Describe what a dispersion strengthened (particulate) composite is such as Al203—Al, what they are good for, and what has to be considered to make a good one. noble [3&03~ A'Q "DJg‘LeQA-m sVagEkva—i PM'L -paggB- 18. (8190:7115) Draw a graph showing how the relaxation modu us E for a thermoplastic polymer varies as a function of temperature. Indicate on your plot the following regimes and temperatures: Glassy, rubbery, viscous flow, leathery, glass transition temperature, and melting temperatures. Show also using a dashed line the behavior of a mostly crystalline polymer of similar composition. 20. (619017133) Most ceramics are highly brittle because the stress at a crack tip is not reduced (as it is by plastic flow 111 metals). Explain (one possible method) how the fracture toughness (Km) of a ceramic can be increased. A sketch of a microstructure might be useful. wages— 21‘. (6190mm) A continuous and aligned glass reinforced composite consists of 55 vol % of glass fibers having a modulus of elasticity of 82 GPa and 45% of a polyester resin that displays a modulus of 3.2 GPA. Compute the modulus of elasticity in the longitudinal (parallel to fibers) and transverse ' (perpendicular to fibers) direction. ' - E V: U m 1-") S .} Fl 3' Sr fixing .L’L' 2' 22. (6 points) Sketch and label molecules of PVC (polyvinyl chloride, Cl sidegroup, monomer formula CZCIHQ) showing the difference between an atactic and an isotactic arrangemement. Which is more likely to _becrysta]lizable? {4 u. H n u H H H :J' I l - l i C16: \-\<~r_ Rr—C—\ __‘C_‘C__é_.c_c‘:-—c‘-C-C— l; C(L it {L (1’ B P: T" 11’ F- ‘45 23. (8 points) The radius of the magnesium ion is 0.072 nm, and the radius of oxygen is 0.140 nm. (a) What will be the coordination number of the Mg ion? You must show a calculation and your reasoning. (b) Compute the density of this material (atomic mass Mg: 24.3, 0 = 16) Coordination Number Radius ratio 2 <0.155 3 0155-0225 fills 2: E1312 :5 J. 4 , 0.2250414 ___. c, la 0 2. 6 0,414.0.732 310 8 0732—1000 c p _ 6- Mud and“ ._ m ,g was, enigma «toy-a. — H o ' . {a Mamrg Hfi'taagwh: w)?” 13 ememo 7 “:5 \fPQAA—v. ~41) {MAJ—6252‘ :E’71CO%1AA\; ) 1 am 2 6-b7ézmgm cm? W :: 26-75 -?- .._ _. _ 7. \c: -_- . '3 J o'b’réz '5 5‘ W/c,“ 24. (6p0ints) Ifthe weight average degree of polymerization in some polypropylene is 27500, what is the weight average molecular weight? Would the number average be higher or lower? Atomic weights: C : 12, H :1, C1 = 35.4 '“w ‘7; .. 1&2 mm -_ ongoorltl ’ — useooo we“ at a e .; News) -page7- 26. (6 points) Sketch (a) block (b) random and (c) graft copolymer molecules using A and B for the two Iner types -pages- ...
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