Lecture 10-16

# Lecture 10-16 - Phase Equilibrium I When aluminum is cold...

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Phase Equilibrium - I

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When aluminum is cold worked: A. Small precipitates form to block dislocation movement B. The grains of aluminum divide and form smaller grains C. Shape changes because of a reduction in surface tension D. Both A and B E. None of the above
During recrystallization: A. Small grains grow to large grains B. Dislocations disappear C. Small grains form D. Both B and C E. None of the above

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FCC metals: A. Have 12 slip systems B. Cannot deform under compression C. Never work harden D. Both A and C E. None of the above F. Two trucks
Phase diagrams A phase is the state of matter Consider water Solid Liquid Vapor A phase diagram is a map of the state of matter versus external conditions

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State of water as a function of temperature
Boiling point of water as a function of pressure

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Phase diagram of water
9 Phase Equilibria: Solubility Limit Introduction Solutions solid solutions, single phase Mixtures more than one phase Solubility Limit : Max concentration for which only a single phase solution occurs. Question: What is the solubility limit at 20 ° C ? Answer: 65 wt% sugar . If C o < 65 wt% sugar: syrup If C o > 65 wt% sugar: syrup + sugar. 65 Sucrose/Water Phase Diagram Pure Sugar Temperature (°C) 0 20 40 60 80 100 C o =Composition (wt% sugar) L (liquid solution i.e., syrup) Solubility Limit L (liquid) + S (solid sugar) 20 4 0 6 0 8 0 10 0 Pure Water Adapted from Fig. 9.1, Callister 7e.

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10 Components : The elements or compounds which are present in the mixture (e.g., Al and Cu) Phases : The physically and chemically distinct material regions that result (e.g., a and b ). Aluminum- Copper Alloy Components and Phases a (darker phase) b (lighter phase) Adapted from chapter-opening photograph, Chapter 9, Callister 3e.
11 Effect of T & Composition ( C o ) Changing T can change # of phases: Adapted from Fig. 9.1, Callister 7e. D (100 ° C,90) 2 phases B (100 ° C,70) 1 phase path A to B . Changing C o can change # of phases: path B to D . A (20 ° C,70) 2 phases 70 80 100 60 40 20 0 Temperature (°C) C o =Composition (wt% sugar) L ( liquid solution i.e., syrup) 20 100 40 60 80 0 L (liquid) + S (solid sugar) water- sugar system

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12 Phase Equilibria Crystal Structure electroneg r (nm) Ni FCC 1.9 0.1246 Cu FCC 1.8 0.1278 Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii ( W. Hume Rothery rules ) suggesting high mutual solubility.
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