# Chapter 9 - Chapter 9 1 ANNOUNCEMENTS 3/27 Reading Chapter...

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Unformatted text preview: Chapter 9 - 1 ANNOUNCEMENTS - 3/27 Reading: Chapter 9 Homework #8: 8.31, 8.34, 8.D6 due Tuesday, April 3 Homework #7 is due this Thursday, March 29 Review homework (Ch. 5,7,8) on Thursday 2nd Midterm Thursday, April 5, Chapters 5, 7, 8 Chapter 9 - 2 One-component (Unary) phase diagram Freezing point boiling point H 2 O Chapter 9 - 3 Microstructure determines the material properties. How do we know the microstrcuture? Chapter 9 - 4 ISSUES TO ADDRESS: • When we combine two elements... what equilibrium state do we get? - energy minimum • In particular, if we specify...- a composition (e.g., x wt% Cu – y wt% Ni), and- a temperature ( T ) then... How many phases do we get? What is the composition of each phase? How much ( volume fraction ) of each phase do we get? Chapter 9: Phase Diagrams Phase B Phase A Nickel atom Copper atom Chapter 9 - 5 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 ? Sucrose/Water Phase Diagram Pure Sugar Temperature (°C) 20 40 60 80 100 L (liquid solution i.e., syrup) Solubility Limit L (liquid) + S (solid sugar) 20 40 60 80 100 Pure Water Adapted from Fig. 9.1, Callister 7e. Answer: 65 wt% sugar . If C o < 65 wt% sugar: syrup If C o > 65 wt% sugar: syrup + sugar. 65 Chapter 9 - 6 • 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., α and β ). Al-Cu Alloy Components and Phases α- Al (dark phase) β-Cu (light phase) Adapted from chapter- opening photograph, Chapter 9, Callister 3e. Chapter 9 - 7 Effect of T & Composition ( C o ) • Changing T can change # of phases: path A to B Adapted from Fig. 9.1, Callister 7e. • Changing C o can change # of phases: path B to D D (100°C,90) 2 phases B (100°C,70) 1 phase A (20°C,70) 2 phases 70 80 100 60 40 20 Temperature (°C) C o =Composition (wt% sugar) L ( liquid solution i.e., syrup) 20 100 40 60 80 water-sugar system L (liquid) + S (solid sugar) Chapter 9 - 8 Phase Equilibria Crystal Structure electronegativity 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. Simple solution system (e.g., Ni-Cu solution) • Ni and Cu are totally miscible in all proportions. Chapter 9 - 9 Phase Diagrams • Indicate phases as function of T , C o , and P . • For this course:- binary systems: just 2 components....
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Chapter 9 - Chapter 9 1 ANNOUNCEMENTS 3/27 Reading Chapter...

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