2010-02-17 Chapter 09 Phase Diagrams

2010-02-17 Chapter 09 Phase Diagrams - Chapter 9 - 1 ISSUES...

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Unformatted text preview: Chapter 9 - 1 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? Chapter 9: Phase Diagrams Phase B Phase A Nickel atom Copper atom Chapter 9 - 2 • 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 ). Aluminum- Copper Alloy Components and Phases α (darker phase) β (lighter phase) Adapted from chapter-opening photograph, Chapter 9, Callister 3e. Chapter 9 - 3 TERMINOLOGY Pure metal of only one type of atom is practically not possible. 99.9999% pure metal will have 10 22 to 10 23 impurity atoms per m 3 In Alloys , impurity atoms are intentionally added to enhance mechanical strength and corrosion resistance. e.g. Sterling Silver contains 92.5% silver and 7.5% copper by weight. Solvent represents element or compound that present in greatest amount. Also called host atoms . Silver in Sterling Silver is solvent. Solute denote element or compound present in minor concentration. Copper in Sterling Silver is solute . In solid solution , solute atoms are added in host atoms such that crystal structure is maintained and, no new microstructure is formed. Solute atoms (or, impurity atoms or, alloying element atoms or, point defects) are uniformly dispersed within the solid. Chapter 9 - 4 DEFINITIONS • Solid solution consists of atoms of at least two different types; the solute atoms occupy either substitutional or interstitial positions in the solvent lattice; and the crystal structure of the solvent is maintained . • Solubility Limit : For many alloy systems; at some specific temperature , there is a max concentration of solute atoms that may dissolve in the solvent to form a solid solution; this is called as solubility limit. Solubility limit is a function of temperature, composition, and pressure. Note: Composition is sometimes referred as Concentration. 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 ? 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) 20 40 60 80 100 =Composition (wt% sugar) 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. Chapter 9 - 6 Effect of T & Composition ( C o ) • Changing T can change # of phases: Adapted from Fig. 9.1, Callister 7e....
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This note was uploaded on 09/30/2011 for the course PHYSICS 1410 taught by Professor Falco during the Spring '08 term at Texas State.

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2010-02-17 Chapter 09 Phase Diagrams - Chapter 9 - 1 ISSUES...

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