ENGR 220 Lecture 7 Chapter 4 All Except 4.11
Crystal Wall Gazing Reading
Quiz on chapter 2 and chapter 3 No equation provided
HW Week 3 4.1,4.5,4.6,4.26
Midterm Next Week 1,2,3,4
show all work in neat order to get partial credit
1.
Assumption A. Perfect Order 1. Throughout crystalline materials 2. On both the atomic scale and on longer sized scale B. Idealized 1. Does not exist in practice 2. Real materials have various defects a) Responsible for observed properties b) Not necessarily bad C. Irregularities 1. Lattice irregularities 2. Can be 1,2 or 3D 3. Atomic diameter in size a) Needs use of microscope to see D. Solidification 1. Nuclei a) Small crystallite Crystallite a) Crystallite growth 3. Grains a) Crystallite ordered form 4. Boundaries a) Grain boundaries
I1.
Imperfections in Solids A. Solidification 1. Casting
a) Result of casting of molten materials (1) Usually metals 2. 2 steps a) Nuclei b) Crystallites 3. Crystals grow until they meet each other B. No Perfect Crystal 1. What are the imperfections a) impurities b) atomic scale disorder c) Etc 2. Why Important a) Effect the properties 111. Polycrystalline Materials A. Grain Boundaries 1. Interfaces between individual crystals 2. Transition from lattice of one region (grain) to that of an adjacent one 3. Somewhat disordered a) Usually at the transition of regions b) Angle of misalignment IV. Types of Imperfections A. Point Defects - At the scale of Atom 1. Vacancies a) Missing Atoms 2. Interstitial Atoms a) Between Atoms 3. Substitutional Atoms a) Does Not belong but is present B. Line Defects 1. Dislocations a) Shift b) Out of place C. Area Defects 1. Grain Boundaries a) Over a larger surface area V. Point Defects A. Vacancies 1. Vacant or empty atomic site a) Distortion comes b) All crystalline solids contain vacancies c) Increases the entropy (level of disorder) of the crystal 2. Equilibrium Concentration a) Vacancy concentration b)
3. Arrhenian Equation a) Thermally activated process b)
-- Activation Energy 1 In(Number Vacancies)=In(Number of Atoms) Boltzmann's Constant Temp . e Kel B. Self-Interstitial 1. Extra atoms positioned between regular atomic sites
VI. Solutions A. Liquid Solutions 1. Immiscible a) Oil and Water 2. Miscible a) Alcohol and Water B. Solid Solutions 1. Immiscible 2. Miscible a) Total or Complete Solid Solution b) Partial Solid Solution VII. Solid Solution A. Substitutional 1. Small differences in size between solvent and solute atoms a) Eg. Cu in Ni B. Interstitial 1. Large difference in radii between solvent and solute 2. Fit between the other atoms a) Eg.C i