L2324BinaryPhDi145s09

L2324BinaryPhDi145s09 - Lectures 23 24 Two-Component Phase...

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Lectures 23 & 24, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R §10.7-9, 10.11, 10.12 Learning objectives: Know and use new concepts for binary phase diagrams Liquidus curve Solidus curve Lever rule Compositions of phases Fractions of each phase Understand the changes that occur during solidification Apply these concepts for a continuous solid solution Understand binary eutectic phase diagrams New feature: solvus curve What happens at the eutectic temperature and composition Difference between primary solid and eutectic solid Use the lever rule to compute fractions of primary, eutectic, or total fractions of two different solid phases Lectures 23 & 24: Two-Component Phase Diagrams 1
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Lectures 23 & 24, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Phases & Components — What’s the Difference? Phase: a chemically and structurally homogeneous portion of a system Diamond and graphite: distinct solid phases of carbon Silica glass, quartz, and cristobalite: distinct phases of SiO 2 Number of components: the minimum number of chemical species needed to describe the composition of every phase Examples: Pure ice in pure water: two phases, one component In a one-component system, all phases have the same composition Ethanol in water: one phase, two components Dry air: one phase, many components 2
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Lectures 23 & 24, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University A map Areas: ranges of T and P for which a single phase is the equilibrium assemblage for the system Curves: combinations of T and P for which two phases coexist at equilibrium Triple point: unique values of T and P for which three phases coexist OGC Fig. 10.21 Review: One-Component Phase Diagrams [OGC §10.6] 3
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4 Lectures 23 & 24, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Coexistence of phases  phases have equal Gibbs free energy (∆G transformation = 0) determines the location of the curves and triple point(s) on one-component phase diagrams OGN Fig. 13.10 ( 29 ( 29 2 2 H O H O s O l ( 29 ( 29 2 2 H O H O s O l Review: Gibbs Free Energy in One-Component Systems [OGN §13.7] G freezing >0 G freezing <0 = ∆ - ∆ freezing freezing freezing G H T S G freezing = 0
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Lectures 23 & 24, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Two-component (a.k.a.
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L2324BinaryPhDi145s09 - Lectures 23 24 Two-Component Phase...

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