Chapter 9- Phase Diagrams

Chapter 9- Phase Diagrams - Chapter 9: Phase Diagrams...

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Chapter 9: Phase Diagrams 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? • What are phases? Phase B Nickel atom Copper atom Phase A Chapter 9 - 1
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One-component (Unary) Phase Diagram Phase is a part of a macroscopic physical system that have relatively uniform chemical composition and physical properties Chapter 9 - 2 Invariant point (triple point)
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Polymorphism Polymorphs exist when there is more than one way for the particles (molecules) of a particular substance to arrange themselves into a crystalline array. Substances that have polymorphs include water, ice, steel, iron Polymorphic types of ice: Hexagonal Cubic Low-density amorphous High-density amorphous Everyday ice and snow is hexagonal ice (I h ). Subjected to higher pressures and varying temperatures, ice can form in roughly a dozen different phases (II- XI). Chapter 9 - 3 Credit: Wilson Bentley
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Alloys Two outcomes if solute atoms (B) are added to solvent (A): Solid solution of B in A (i.e., random dist. of point defects) Chapter 9 - 4 • Solid solution of B in A plus particles of a new phase (usually for a larger amount of B) OR Substitutional solid soln. (e.g., Cu in Ni ) Interstitial solid soln. (e.g., C in Fe ) Second phase particle --different composition --often different structure .
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Components and Phases Components : The elements or compounds which are present in the mixture (e.g., Al and Cu) Phases : The physically and chemically distinct material regions (e.g., α and β ). Aluminum- Copper Alloy α (darker phase) β (lighter phase) Adapted from chapter-opening photograph, Chapter 9, Callister 3e. Chapter 9 - 5
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Specification of Composition Composition – relative content of a specific element in an alloy 100 x 2 1 1 1 m m m C + = weight (mass) percent m 1 = mass of component 1 m 2 = mass of component 2 100 x 2 1 1 ' 1 m m m n n n C + = atom percent n m1 = number of moles of component 1 n m1 = m 1 (g)/ A 1 (g/mole) Chapter 9 - 6
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Chapter 9 - 7 Phase Equilibria: Solubility Limit Introduction – Solutions – solid solutions, single phase –M i x t u r e s – 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 Sugar/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 40 60 80 100 Water Adapted from Fig. 9.1, Callister 7e.
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Effect of T & Composition ( C o ) Chapter 9 - 8 • Changing T can change # of phases: Adapted from Fig. 9.1, Callister 7e.
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This note was uploaded on 04/02/2008 for the course MSE 200 taught by Professor Wholedepartment during the Spring '08 term at N.C. State.

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Chapter 9- Phase Diagrams - Chapter 9: Phase Diagrams...

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