E4511ps5-txt - (a) network structures, as in quartz; (b)...

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Page 1 Engineering 45 The Structure and Properties of Materials Spring, 2011 Problem Set No. 5 Problem 1: (a) Describe how the unusual properties of an elastomer are determined by its structure. (b) Draw the molecular structure of rubber. Explain why natural rubber becomes an exceptionally good elastomer when it is "vulcanized" with sulfur. Problem 2: (a) In simple terms, how does the structure of a thermosetting polymer differ from that of a thermoplastic polymer? (b) Thermoplastic polymers tend to be ductile, and easily formed into complex shapes by heating to moderate temperature. Thermosetting polymers tend to be brittle, and must be molded or cast into their final shapes, but can be made much stronger than the thermoplastics. Discuss this behavior in terms of their structure. Problem 3: The basic structural unit of the silicate minerals is the (SiO 4 ) -4 tetrahedron. De- scribe how these tetrahedra can bond to one another to form:
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Unformatted text preview: (a) network structures, as in quartz; (b) sheet structures, as in mica; (c) linear structures, such as asbestos. Problem 4: (a) While silica can be made into a glass by cooling it quickly from the liquid state, most common silica glasses include ionic species such as Na + or oxides that crystallize in very different crystal structures, such as PbO 2 , to promote glass formation. Why? (b) Silica glass can be easily formed into elegant stemware or blown into complex ornamental shapes, while crystalline quartz is much more difficult to fabricate in useful shapes. Why? (Note that "crystal" glassware isn't.) Engineering 45: Spring, 2011 Problem Set No.5 page 2 Problem 5: Given the second law of thermodynamics, show: (a) the condition of thermal equilibrium: the temperature of a system is constant at equilibrium; (b) the condition of chemical equilibrium: the chemical potential of any chemical component is constant at equilibrium....
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This note was uploaded on 04/05/2011 for the course ENGIN 45 taught by Professor Devine during the Spring '07 term at Berkeley.

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E4511ps5-txt - (a) network structures, as in quartz; (b)...

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