This preview shows pages 1–31. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Chapter 4: Crystal imperfections Reading assignment Chapter 4 Crystalline material Noncrystalline material Defect types Point defect : associated with 1 or 2 atomic positions); vacancy, solute atom or interstitial. Line defect : 1D; dislocations Surface defect : 2D; grain boundaries and external surfaces. Point defects Vacancy Interstitial atom Small substitutional atom Large substitutional atom Point defects: vacancy and interstitial Vacancy, a point defect A vacancy is produced when an atom is missing from a normal lattice site. Vacancies are introduced during solidification, at high Ts, or as a consequence of radiation damage. *Same number of atoms Without Vacancies With Vacancies /RT H V v e X where H v = energy of formation of a mole of vacancy, R = gas constant = 8.3143 J mole1 and T = temperature in K. Fraction of atom sites vacant T X V 1 The larger is H v , the smaller is X V . This is because the larger is H v , the more is the energy needed to form a vacancy. An alternative form of the above expression is , /kT h V v e X where h v = energy of formation of a single vacancy, = k = Boltzmanns constant = N = Avogadros number and T = temperature in K. N H v N R Let X V1 be the value of X V when T = T 1 Let X V2 be the value of X V when T = T 2 Let A be the proportionality constant, so that  = = = = = 1 2 v 1 v 2 v 2 v 1 v v T 1 T 1 R H /R T H /R T H V1 V2 /R T H V2 /R T H V1 /R T H V e Ae Ae X X Hence, Ae X Ae X Then Ae X  =  = 1 2 V V1 V2 10 1 2 V V1 V2 T 1 T 1 2.3R H X X log T 1 T 1 R H X X ln Thus, if H v is known and X V1 is known for T=T 1 , then the above equation can be used to calculate X V2 for T=T 2 . Vacancy in an ionic solid Schottky defect Impurity A point defect impurity alloying element solvent: the element or compound in a solution (alloy), present in the greatest amount. host atoms solute: element or compound in minor concentration. solid solution: an alloy resulting by the addition of solute atoms to the solvent. Types of impurity Substitutional impurity Interstitial impurity Impurities in Solids: Solid Solutions Contamination of materials is unavoidable.Contamination of materials is unavoidable....
View
Full
Document
This note was uploaded on 12/19/2010 for the course MAE 381 taught by Professor Chung during the Spring '08 term at SUNY Buffalo.
 Spring '08
 CHUNG

Click to edit the document details