201 Week 6 2008 Posted

201 Week 6 2008 Posted - Chapter 9: Phase Diagrams ISSUES...

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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
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Chapter 9 - Phase Diagrams A phase diagram shows what phases are present at equilibrium for a given temperature, pressure and composition A phase is a part of material having uniform structure and composition. It can be solid, liquid or gas. Distinct phases in a system have physically or chemically distinct characteristics. (e.g. FCC and BCC iron, water and ice) Component = The elements or compounds which are present in the mixture
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Chapter 9 - One Component Phase Diagrams Pressure H 2 O
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Chapter 9 - Pressure Temperature 14 kBar 1000 K 34 kBar Graphite Diamond 300K 1 Bar = 10 5 Pa 1 atm At room temperature and 1 atm, carbon should be graphite. So why can people buy diamond rings? Carbon Phase Diagram
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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) 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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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 ). Aluminum- Copper Alloy Components and Phases α (darker phase) β (lighter phase) Adapted from chapter-opening photograph, Chapter 9, Callister 3e.
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Chapter 9 - 7 Effect of T & Composition ( C o ) Changing T can change # of phases: Adapted from Fig. 9.1, Callister 7e. 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 (liquid) + S (solid sugar) water- sugar system
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Chapter 9 - 8 Phase Equilibria Crystal Structure electroneg r (nm) Ni FCC 1.9 0.1246 Cu 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.
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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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201 Week 6 2008 Posted - Chapter 9: Phase Diagrams ISSUES...

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