Lecture3

Lecture3 - ENGR166 Foundations of Engineering Instructor Dr...

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ENGR166 Foundations of Engineering Required text “Materials In Today’s World” Peter A. Thrower, Jr., 2nd edition, McGraw-Hill Companies, Inc (1996) Instructor Dr. Daniel Goberman [email protected] 486-5478 Office: UTEB. Rm 266 Class Web Site http://www.ims.uconn.edu/~goberman/ENGR166/index.html
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Structure of Materials Five levels of structure: electronic structure, atomic structure, crystal structure, microstructure and macrostructure Bonding between atoms (electronic & atomic structure) determines structure at higher levels (crystal, micro- and macro-structure) Structure & defects in structure ultimately determine material properties Outline: Types of bonding (Ch. 5) Crystal structures, non-crystallinity (Ch. 6 & 7) Defects in crystals (Ch. 8)
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Quick Review…of Thurs
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Types of Bonding Depending on the type of each atom and the environment each atom sees, several bonding types arise Primary bonds (strong): metallic, ionic, covalent Secondary bonds (weak): hydrogen & van der Waals Generally, combination of more than one type of bonding exists in a solid
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Metallic bonds Metallic elements have only one, two, or at most three valence electrons. In a metallic solid, the atoms give up all valence electrons to a “common pool” or “sea” of electrons. The remaining non-valence electrons and nuclei form positive ion “cores”. The valence electrons are free to drift throughout the entire lattice and act as electron glue holding the material together Metallic bonds have no directionality and are strong in all directions. They are good electrical and thermal conductors because of the free electrons Atoms can pack closely, as a result, metals are heavy and dense Atoms can move over each other and change position relatively easily (more about this later). So, metals can be formed by pressing, forging, rolling, etc. Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Positive ion cores electrons
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Ionic Bonds Examples: NaCl, Al 2 O 3 , MgO, CaO, H 2 O In ionic materials, atoms achieve their eight electrons in the outer shells by giving up valence electrons (e.g., Na) or by accepting electrons (e.g., Cl).
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Lecture3 - ENGR166 Foundations of Engineering Instructor Dr...

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