10.Phase%20Diagrams-1 - Phase Diagrams Reading: Callister...

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1 Phase Diagrams Reading: Callister Ch. 10 • What is a phase? What is the equilibrium state when different elements are mixed? • What phase diagrams tell us. • How phases evolve with temperature and composition (microstructures). β (lighter phase MSE280 © 2007-2009 Moonsub Shim, University of Illinois 1 α (darker phase) phase) 1 Diff t h i l t t li id lid Phases Phase: A homogeneous portion of a system that has uniform physical and chemical characteristics. 1. Different physical states: vapor, liquid, solid e.g. water MSE280 © 2007-2009 Moonsub Shim, University of Illinois 2
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2 Phases 2. Different chemical compositions e.g. sugar water Solubility Limit : Max concentration for which only a solution occurs. MSE280 © 2007-2009 Moonsub Shim, University of Illinois 3 Question: What is the solubility limit at 20C? Answer: 65wt% sugar . If C o < 65wt% sugar: syrup If C o > 65wt% sugar: syrup + sugar. Solubility limit increases with T: e.g., if T = 100C, solubility limit = 80wt% sugar. Components : elements or compounds which are mixed initially (e.g., Al and Cu) Phases : physically and chemically distinct regions that result Aluminum- Copper Alloy α (darker phase) β (lighter phase) (e.g., α and β ). Plain carbon steel MSE280 © 2007-2009 Moonsub Shim, University of Illinois 4
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3 Temperature and composition B C A MSE280 © 2007-2009 Moonsub Shim, University of Illinois 5 A : 2 phases present (liquid solution and solid sugar) B : Single phase C : back to 2 phases but at different composition Note: this is an equilibrium phase diagram (What does it mean to have phase equilibrium?) Phase Equilibrium Equilibrium: minimum energy state for a given T, P, and composition (i e equilibrium state will persist and composition (i.e. equilibrium state will persist indefinitely for a fixed T, P and composition). An equilibrium phase will stay constant over time. Phase diagrams tell us about equilibrium phases as a function of T, P and composition (here, we’ll always keep P constant for simplicity) MSE280 © 2007-2009 Moonsub Shim, University of Illinois 6 keep P constant for simplicity).
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4 Unary Systems Single component system Consider 2 elemental metals separately: Cu has melting T = 1085 o C Ni has melting T = 1453 o C (at standard P = 1 atm) liquid T 1453 o C liquid T MSE280 © 2007-2009 Moonsub Shim, University of Illinois 7 1085 o C Cu solid Ni solid What happens when Cu and Ni are mixed? Criteria for Solid Solubility Simple system (e.g., Ni-Cu solution) Element Atomic Crystal Electro- Valence • Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii ( W. Hume – Rothery rules ) suggesting high mutual solubility. • Ni and Cu are totally Radius Structure nega- (nm) tivity Cu 0.1278 FCC 1.9 +2 C 0.071 H 0.046 O 0.060 Ag 0.1445 FCC 1.9 +1 Al 0.1431 FCC 1.5 +3 Co 0.1253 HCP 1.8 +2 MSE280 © 2007-2009 Moonsub Shim, University of Illinois 8 soluble in one another for all proportions.
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This note was uploaded on 03/15/2010 for the course MSE 280 taught by Professor Johnson during the Fall '08 term at University of Illinois, Urbana Champaign.

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10.Phase%20Diagrams-1 - Phase Diagrams Reading: Callister...

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