L18Glass145s10

L18Glass145s10 - Lecture 18, spring 2010 ENGR 145,...

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Unformatted text preview: Lecture 18, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R 3.21; 4.6, 4.11-4.12; 11.13-11.17; 14.7; OGC p.887 Learning objectives: Understand the differences in structure between crystalline and glassy materials Understand the nature of the glass transition Describe how the structural features of a polymer can affect its glass transition and melting temperatures Lecture 18: Noncrystalline Solids & Semicrystalline Solids 1 Obsidian, a naturally occurring volcanic glass Lecture 18, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Covalent crystals Although bonding influences local symmetry Noncrystalline solids (glasses) have structures that satisfy local bonding requirements without 3-D periodicity Ionic crystals Metallic crystals 2 Lecture 18, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Crystalline vs. Noncrystalline Structures [C&R 3.21] Crystalline structures Short-range order (SRO) local bonding and long-range order (LRO) 3-D, periodic arrangement of atoms Non-crystalline structures (glasses) SRO satisfies local bonding No LRO random network C&R Figure 3.40 3 Lecture 18, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Oxides; also some sulfides, selenides, E.g. SiO 2 Si-O tetrahedra (CN Si = 4) sharing corners (CN O = 2) as in crystalline forms of SiO 2 ( e.g. quartz) Lack of crystallinity made possible by Rotation about the Si-O-Si bond Some variability in the Si-O-Si bond angle satisfies local bonding requirements without 3-D periodicity Inorganic Glasses Fiber optic wave- guides of silica glass (OGC Figure 21.31) 4 Lecture 18, spring 2010...
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This note was uploaded on 01/30/2011 for the course EMSE 103 taught by Professor Ggh during the Spring '10 term at Case Western.

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L18Glass145s10 - Lecture 18, spring 2010 ENGR 145,...

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