ECE331 Wi11 lecture 6

ECE331 Wi11 lecture 6 - LAST TIME: Equilibrium...

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LAST TIME : Equilibrium Concentration: Equilibrium concentration varies with temperature! Point Defects No. of defects Activation energy N v N = exp Q v k T No. of potential defect sites. emperature Boltzmann's constant (1.38 x 10 -23 J/atom-K) Temperature (8.62 x 10 -5 eV/atom-K) Each lattice site a potential is a potential vacancy site
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Today, start with Impurities in olids Impurities also form a type of point defect, but they are Solids py p p , y “extrinsic” (as opposed to “intrinsic” in origin) Substitutional impurity : when an impurity atom exactly replaxes (substitutes) for a host atom in the crystal Interstitial impurity : when an impurity atom resides at an interstitial location in the crystal y
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Impurities in Solids Two outcomes if impurity (B) added to host (A): (1) Solid solution of B ( solute ) in A ( solvent ) (random dist. of point efects) defects) OR Substitutional solid soln. g u i Interstitial solid soln. g e (e.g., Cu in Ni ) (e.g., C in Fe ) Ideal solid solution: Impurities do not alter crystal structure of host solid material
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Impurities in Solids (2) Solid solution of B in A plus particles of a new phase (usually for a larger amount of B) Second phase particle --different composition --often different structure. SAVE THIS TYPE OF MULTI-PHASE STRUCTURE FOR LATER! lloy: solid solution with solute concentration > approx Alloy: a solid solution with solute concentration > approx.
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This note was uploaded on 04/30/2011 for the course ECE 331 taught by Professor Rajan during the Spring '09 term at Ohio State.

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ECE331 Wi11 lecture 6 - LAST TIME: Equilibrium...

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