2011 APS104-MSE-Chapter05-NPK-L27[1].pdf

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Published on 15 Apr 2013
School
UTSG
Department
Chemical Engineering and Applied Chemistry
Course
APS104H1
Professor
Chapter 5 -
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Chapter 5 -2
ISSUES TO ADDRESS...
What types of defects arise in solids?
• Can the number and type of defects be varied
and controlled?
How do defects affect material properties?
Are defects undesirable?
CHAPTER 5:
IMPERFECTIONS IN SOLIDS
•Reading: pp128 136, 140-147
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Chapter 5 -3
Solidification- result of casting of molten material
2 steps
Nuclei form
Nuclei grow to form crystals grain structure
Start with a molten material all liquid
Imperfections in Solids
Crystals grow until they meet each other
Adapted from Fig. 5.19 (b), Callister & Rethwisch 3e.
grain structure
crystals growing
nuclei liquid
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Document Summary

Issues to address: what types of defects arise in solids, can the number and type of defects be varied and controlled, how do defects affect material properties, are defects undesirable, reading: pp128 136, 140-147. Imperfections in solids: solidification- result of casting of molten material. 2 steps: nuclei form, nuclei grow to form crystals grain structure, start with a molten material all liquid nuclei liquid crystals growing grain structure. 5. 19 (b), callister & rethwisch 3e: crystals grow until they meet each other. There is no such thing as a perfect crystal. Many of the important properties of materials are due to the presence of imperfections. Types of imperfections: vacancy atoms, interstitial atoms, substitutional atoms, dislocations, grain boundaries, cracks, pores. Vacant atomic sites in a structure. distortion of planes: self-interstitials: extra atoms positioned between atomic sites. distortion of planes. Equilibrium concentration: point defects: equilibrium concentration varies with temperature! Boltzmann"s constant (1. 38 x 10-23 j/atom-k) (8. 62 x 10-5 ev/atom-k)

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