Lecture1810fc

Lecture1810fc - Chemistry 83 11/04/10 Technologies for...

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Chemistry 83 11/04/10 1 Technologies for Materials Society uses materials to provide shelter, clothing, tools, and weapons Properties of materials depend on their bonding and structures Ionic substances Ceramics/insulators Glass Metallic substances Structural materials Materials that conduct heat/electricity Molecular covalent substances Polymers/plastics/elastomers Network covalent substances Semiconductors Low temperature superconductors High temperature superconductors Composites
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Chemistry 83 11/04/10 2 Technologies for ceramics and glasses have been available since 9000 BC • Ceramics are ionic substances formed by heating mixtures of ionic substances to high temperatures • Ceramics involve repeating structures of ions held together by ionic bonds (crystalline substances) • Frequently involves oxides that are able to resist reaction when exposed to air • Most common involve clay Al 2 O 3 .2SiO 2 .2H 2 O Ceramics have useful properties • Typical ionic: brittle, high MP and BP • Not subject to corrosion since they are fully oxidized • Poor conductors of heat and electricity since ions are not free to move in solid: – Used as thermal insulators in construction (bricks and concrete), ±re places, furnaces, smoke stacks, shuttle nose cone (SiC), etc. – Ceramics are used as electrical insulators • Use of very high temperatures produces glazed ceramics with surfaces that are impervious to water
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Chemistry 83 11/04/10 3 Fine/Beal, Chemistry for Engineers and Scientists, Saunders, NY, 1990, 694 Ceramic - crystalline structure Glass - amorphous structure *Si = red, O = gray, Na = yellow Structural difference between a ceramic and a glass * * Technologies for obtaining and using metals have been available since 6000 BC • Some unique properties of metals that make them useful to society: – Luster – Malleability – Ductile – Electrical Conductivity Conduct electricity at room temperature Conductivity decreases as temperature increases http://www.hometrainingtools.com/articles/learn-about-metals-science-teaching-tip.html
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Lecture1810fc - Chemistry 83 11/04/10 Technologies for...

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