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Chapter6 - Chapter 6 Noncrystalline and Semicrystalline...

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Chapter 6 Noncrystalline and Semicrystalline Materials Introduction Glass Transition Temperature Viscous Deformation Structure and Properties of Amorphous Oxide Glasses Structure and Properties of Amorphous and Semi-crystalline Polymers Structure and Properties of Rubbers and Elastomers Metallic Glasses
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Introduction The emphasis thus far has been on crystalline materials. There are numerous engineering materials that lack the long range translational periodicity of a crystalline material. These non-crystalline materials are referred to as either- amorphous, glassy, or super- cooled liquids. Theoretically, any material can form an amorphous structure if solidified at sufficiently high enough rates. This chapter will emphasize the structural considerations that facilitate the development of an amorphous structure.
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Some Glass Forming Systems Elements S, Se, P Oxides SiO 2 , B 2 O 3 , P 2 O 5 , GeO 2 , AsO 2 Halides BF 2 , AlF 3 , ZnCl 2 , Ag(Cl,Br,I),Pb(Cl 2 ,Br 2 ,I 2 ) Sulfides As 2 S 3 , Sb 2 S 3 Selenides Various compounds of Tl, Sn, Pb, As, Sb, Bi, Si, and P Tellurides Various compounds of Tl, Sn, Pb, As, Sb, Bi and Ge Nitrides KNO 3 -Ca(NO 3 ) 2 and many mixtures containing alkali and alkaline earth nitrates Sulfates KHSO 4 and many other binary and ternary mixtures Carbonates K 2 CO 3 -MgCO 3 Polymers Polystyrene, PMMA, polycarbonate, PET Metallic Alloys Au 4 Si, Pd 4 Si, (Fe-Si-B) alloys, Al-transition metal rare earths
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Specific Volume for a Variety of Materials Liquid to glass solid transformation in a pure substance. The glass transition temperature, Tg, is not an equilibrium transformation temperature. Liquid to crystalline solid transformation for a pure substance. T m is an equilibrium transformation temperature
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The Effect of Cooling Rate on the Glass Transition Temperature, T g Specific Volume T g1 T g2 T m Temperature T 1 . T 2 . T 1 . T 2 . Liquid Liquid Solid Glass Super-cooled liquid Super-cooled liquid >
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The above figure describes the variation in specific volume of a pure substance undergoing a liquid to solid phase transformation. On the same plot the variation in specific volume is shown for a super-cooled liquid cooled to produce a glassy structure. 1. Plot the variation in entropy as a function of temperature for these two processes. 2. How does cooling rate affect the glass transition temperature? 3. Explain why there should be a lower limit to the glass transition temperature. Question
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The Effect of Cooling Rate on the Glass Transition Temperature, T G Specific Volume Entropy Temperature Glass High Cooling Rate Low Cooling Rate
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Specific Volume for a Variety of Materials Liquid to semi-crystalline solid transformation
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Specific Volume for a Variety of Material Types Liquid to crystalline solid transformation Liquid to glass solid transformation Liquid to semi-crystalline solid transformation
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Comparison of the Response of a Solid and a Liquid to a Shear Stress F dy A dx G τ γ τ γ = ( ) ( ) dy d dt dx dy d dx dt τ τ d dt γ τ η ηγ = = &
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