Lecture5

Lecture5 - ENG166 Foundations of Engineering Instructor Dr....

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ENG166 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
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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) Defects in crystals (Ch. 8)
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Point Defects (0-dimensional) An avenue for atomic motion within the lattice, in response to an external mechanical or electrical load In stainless steel, carbon, which makes it a steel, is an interstitial impurity in the iron lattice (and chromium, which makes it stainless, is a substitutional impurity) In semiconductors, substitutional impurities are called dopants, and control the amount of charge carriers Intrinsic (vacancies) Extrinsic (interstitial and substitutional impurity atoms) Alter the mechanical properties (by affecting slip and dislocation motion), electronic properties (doping in semiconductors), etc.
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Point Defects (0-dimensional) Impurity atoms are ALWAYS in a material Examples where impurity atoms are ‘Bad’: - Ni-based turbine engines. - Chromium for electrical contacts 3
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Point Defects (0-dimensional) Impurity atoms are ALWAYS in a material – Examples where impurity atoms are ‘Bad’ and ‘Good’: - Silicon Zone Refining to remove impurities A solid rod of impure Si is pushed through a furnace (multiple furnace set-up to right). Si melts, entering the furnace, and solidifies while exiting the furnace. Impurity atoms tend to stay in the melt. When finished, one end of rod has high impurity concentration, while other end is very pure. Best purity = 99.9999999% Si 1 impurity for every 10 billion Si atoms. 5
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Impurity atoms are ALWAYS in a material – Examples where impurity atoms are ‘Bad’ and ‘Good’: - Silicon Ion implantation to add Impurities Implantation is like shooting bullets from a machine gun into a wall! B, As, or P can be added to Si
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This note was uploaded on 04/07/2008 for the course MSE 166 taught by Professor Bob during the Spring '08 term at UConn.

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Lecture5 - ENG166 Foundations of Engineering Instructor Dr....

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