Lecture 7 - 8th Ed. Ch. 9

Lecture 7 - 8th Ed. Ch. 9 - Chapter 9 Phase Diagrams 1...

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1 Chapter 9 Phase Diagrams
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ISSUES TO ADDRESS. .. When we combine two elements. .. what equilibrium state do we get? In particular, if we specify. .. --a composition (e.g., wt% Cu - wt% Ni), and --a temperature ( T ) then. .. How many phases do we get? What is the composition of each phase? How much of each phase do we get? Phase Diagrams Phase B Phase A Nickel atom Copper atom
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Phase Diagrams Example: The H 2 O ….Unary (1-component )System
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From: F.P. Bundy, The P,T Phase and Reaction diagram for elemental Carbon, 1979; J. Geophys. Res. 85 (B12) (1980) 6930. Phase Diagrams Example: The Carbon Unary (1-component ) System)
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Phase Diagrams Example: The Carbon Dioxide Unary (1-component ) System)
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Multi-component Phase Diagrams What we will study in this lecture… The Fe-C system (Iron, Steel and Cast Irons)
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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 Water
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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., and ). Aluminum- Copper Alloy Components and Phases (darker phase) (lighter phase)
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Effect of T & Composition ( C o ) Changing T can change # of phases: 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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Phase Equilibria Crystal Structure Electro- negativity 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…hello! ) suggesting high mutual solubility. Simple solution system (e.g., Ni-Cu solution) Ni and Cu are totally miscible in all proportions.
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Phase Diagrams Indicate phases as function of T , C o , and P . For this course: -binary systems: just 2 components. -independent variables: T and C o ( P = 1 atm is almost always used). Phase Diagram for Cu-Ni system • 2 phases: L (liquid) (FCC solid solution) • 3 phase fields: L L + wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T (°C) L (liquid) a (FCC solid solution)
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wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T (°C) L (liquid) (FCC solid solution) Cu-Ni phase diagram Phase Diagrams : # and types of phases Rule 1: If we know T and C o , then we know: --the # and types of phases present.
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Lecture 7 - 8th Ed. Ch. 9 - Chapter 9 Phase Diagrams 1...

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