Chapter 5 - Diffusion in Solids (Chapter 5) What you should...

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1 What you should understand by the end of this chapter: The importance of atomic diffusion for altering the structure of materials. The nature and mechanisms of diffusion. The key role of vacancies in diffusion. Fick’s 1 st law for diffusion. How to solve simple diffusion problems. Diffusion in Solids (Chapter 5)
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2 Diffusion Are solids inert? That is, once a solid forms is its structure fixed forever? ABSOLUTELY NOT One mechanism for altering a solid’s internal structure is diffusion. movement of atoms within a solid (crystalline or amorphous)
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3 Demo: Rates of Diffusion Diffusion in solids is . . . slow. hard to see. Can demonstrate related process in liquid (water) and a gas (air): How long does it take for plastic bag to swell? (~ 5 cm)? How long does it take for a scent to diffuse through the classroom (~ 5 m)? Will give a more quantitative treatment of this later on.
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4 Diffusion Alters Microstructure CuAl 2 precipitates in Al matrix. Heated at 320 o C for 15 minutes.
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5 Vacancy Diffusion Remember, all crystals have vacancies. (X v 10 -4 at T = T M ) Atoms easily hop into vacant lattice positions Process is called substitution. This is a statistical process.
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This note was uploaded on 03/03/2011 for the course MATLS 101 taught by Professor Dr.kish during the Spring '11 term at McMaster University.

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Chapter 5 - Diffusion in Solids (Chapter 5) What you should...

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