ENGR 240 - 9.7.07

ENGR 240 - 9.7.07 - ENGR 240 September 7, 2007 Single...

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ENGR 240 – September 7, 2007 Single Crystals, Polycrystals, Noncrystalline solids o Single crystal – same arrangement of atoms throughout the material o Polycrystals – crystal comprised of many smaller crystals called grains Anisotropic – non-uniform properties; depend on direction vector Found in some single crystals Examples – quartz, calcium fluoride, aluminum oxide Isotropic – properties are the same in all directions (uniform) Seen in highly symmetric single crystals Most commonly found in polycrystalline materials o Usually because grains are randomly oriented o Non-crystalline solids No long range atomic order Amorphous, glassy o Single crystals are stronger than multiple crystals Multiple crystals break at joints, grain boundaries Use single crystal material for turbine blades Thermal Properties of Crystalline vs. Amorphous o Single crystals has a very sharp transition from solid to liquid o Non-crystalline – when cooled you get a super-cooled liquid
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ENGR 240 - 9.7.07 - ENGR 240 September 7, 2007 Single...

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