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19 Cards in this Set
- Front
- Back
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9.2 In terms of bonding, explain why silicate materials have relatively low densities |
The atomic bonds in silicate materials have significant covalent character (Si and O are separatedby just one column in the periodic table). Therefore, the bonds are directional. This limits thepacking efficiency (number of nearest neighbors) of the atoms, and therefore the density |
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9.2 Why do the Frenkel defects for cations greatly outnumber the Frenkel defects for anions in NaCl? |
A Frenkel defect arises when an ion moves from its usual (lattice) site into an interstitial site.In NaCl, the anions (chloride) are significantly larger than the cations (sodium), and thereforemuch less likely to exist as interstitials. |
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9.3 Residual thermal stresses arise when a glass object is cooled. Why? |
Residual thermal stresses are introduced into a glass piece when it is cooled because surface andinterior regions cool at different rates. The viscosity of the glass increases as the temperaturedecreases, so the contraction of the cooler surface cannot keep up with that of the still warmer andtherefore more deformable interior. This differential contraction leads to the build-up of stress. |
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9.3 Are thermal stresses introduced when a glass object is heated? Explain |
Yes.Thermal stresses will be introduced because of thermal expansion upon heating, for the samereason that they arise due to thermal contraction upon cooling |
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9.3 Drying shrinkage is greater for slip cast or hydroplastic products that have smaller clay particles. Why? |
When products consist of smaller clay particles, there is more particle surface area, and,consequently, more water will surround a given volume of particles. The drying shrinkage willthus be greater as this water is removed. |
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9.4 True of False The addition of Ca to ZrO2 creates Shottky defects in the ZrO2 |
False. The addition of Ca to ZrO2 creates anion vacancies. A Shottky defect is a paired set ofcation and anion vacancies. |
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9.4 True of False The addition of Mg to ZrO2 does not create Frenkel defects in the ZrO2 |
True. Frenkel defects are self-interstitials. |
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9.4 True of False The diffusion of oxygen atoms through a Ca-doped layer of ZrO2 is used to measure the concentration of oxygen dissolved in molten steel. |
False. Oxygen ions diffuse through the Ca-doped ZrO2 |
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9.4 True of False Specific volume is the same as mass per unit volume |
False. Specific volume is volume per unit mass. |
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9.4 True of False Inorganic glasses are annealed by heating them to temperatures above the softening point |
False. The annealing range is below the softening point. |
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9.7 Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: - Molecular weight |
The tensile modulus is not directly influenced by a polymer's molecular weight |
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9.7 Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: - Degree of crystallinity |
Tensile modulus increases with increasing degree of crystallinity for semicrystallinepolymers. This is due to enhanced secondary interchain bonding which results from adjacent alignedchain segments as percent crystallinity increases. This enhanced interchain bonding inhibits relativeinterchain motion. |
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9.7 Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: - Deformation by drawing |
Deformation by drawing also increases the tensile modulus. The reason for this is thatdrawing produces a highly oriented molecular structure, and a relatively high degree of interchainsecondary bonding |
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9.7 Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: - Annealing of an undeformed material |
When an undeformed semicrystalline polymer is annealed below its melting temperature,the tensile modulus increases |
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9.7 Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: - Annealing of a drawn material |
A drawn semicrystalline polymer that is annealed experiences a decrease in tensile modulusas a result of a reduction in chain-induced crystallinity, and a reduction in interchain bonding forces. |
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9.6 (1) state whether or not it is possible to determine whether one polymer ismore likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it isnot possible to decide, then state why. - Linear and syndiotactic poly(vinyl chloride); linear and isotactic polystyrene |
Yes, for these two polymers it is possible to decide. The linear and syndiotactic poly(vinylchloride) is more likely to crystallize; the phenyl side-group for polystyrene is bulkier than the Clside-group for poly(vinyl chloride). Syndiotactic and isotactic isomers are equally likely to crystallize. |
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9.6 (1) state whether or not it is possible to determine whether one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. - Network phenol-formaldehyde; linear and heavily crosslinked cis-isoprene |
No, it is not possible to decide for these two polymers. Both heavily crosslinked andnetwork polymers are not likely to crystallize |
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9.6 (1) state whether or not it is possible to determine whether one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. - Linear polyethylene; lightly branched isotactic polypropylene |
Yes, it is possible to decide for these two polymers. The linear polyethylene is more likelyto crystallize. The repeat unit structure for polypropylene is chemically more complicated than is therepeat unit structure for polyethylene. Furthermore, branched structures are less likely to crystallizethan are linear structures. |
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9.6 (1) state whether or not it is possible to determine whether one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. - Alternating poly(styrene-ethylene) copolymer; random poly(vinyl chloride-tetrafluoroethylene) copolymer |
Yes, it is possible to decide for these two copolymers. The alternating poly(styreneethylene)copolymer is more likely to crystallize. Alternating copolymers crystallize more easily thando random copolymers. |
