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Lecture 01

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Lecture 01

  1. 1. INTRODUCTION What is Materials Science??? Structure Properties
  2. 2. INTRODUCTION Materials Engineering: On the basis of materials science, designing and/or engineering the structure of materials to produce desired properties What is Materials Engineering??? Structure Properties Processing
  3. 3. INTRODUCTION Structure Sub-atomic Electronic <0.2 nm 1 nm = 4x10 -8 in Atomic 0.2-10 nm HRTEM, STEM AFM Microscopic 1-1000  m Optical Microscope SEM,TEM, XRD Bulk >1 mm Naked Eye
  4. 4. Properties <ul><li>Mechanical </li></ul><ul><li>Electrical </li></ul><ul><li>Magnetic </li></ul><ul><li>Optical </li></ul><ul><li>Thermal </li></ul><ul><li>Chemical </li></ul>Response to External Stimulation MMAT 201/243 MMAT 244/267 MMAT 234
  5. 5. Structure, Processing, & Properties ex: hardness vs structure of steel • Properties depend on structure Data obtained from Figs. 10.21(a) and 10.23 with 4wt%C composition, and from Fig. 11.13 and associated discussion, Callister 6e . Micrographs adapted from (a) Fig. 10.10; (b) Fig. 9.27;(c) Fig. 10.24; and (d) Fig. 10.12, Callister 6e . ex: structure vs cooling rate of steel • Processing can change structure Hardness (BHN)
  6. 6. ELECTRICAL • Electrical Resistivity of Copper: • Adding “ impurity ” atoms to Cu increases resistivity . • Deforming Cu increases resistivity . Adapted from Fig. 18.8, Callister 6e. (Fig. 18.8 adapted from: J.O. Linde, Ann Physik 5 , 219 (1932); and C.A. Wert and R.M. Thomson, Physics of Solids , 2nd edition, McGraw-Hill Company, New York, 1970.)
  7. 7. THERMAL • Thermal Conductivity of Copper: --It decreases when you add zinc! Adapted from Fig. 19.4, Callister 6e. (Fig. 19.4 is adapted from Metals Handbook: Properties and Selection: Nonferrous alloys and Pure Metals , Vol. 2, 9th ed., H. Baker, (Managing Editor), American Society for Metals, 1979, p. 315.)
  8. 8. MAGNETIC • Magnetic Permeability vs. Composition: <ul><li>Adapted from C.R. Barrett, W.D. Nix, and </li></ul><ul><li>A.S. Tetelman, The Principles of </li></ul><ul><li>Engineering Materials , Fig. 1-7(a), p. 9, </li></ul><ul><li>Electronically reproduced </li></ul><ul><li>by permission of Pearson Education, Inc., </li></ul><ul><li>Upper Saddle River, New Jersey. </li></ul>--Adding 3 atomic % Si makes Fe a better recording medium! Fig. 20.18, Callister 6e. (Fig. 20.18 is from J.U. Lemke, MRS Bulletin , Vol. XV, No. 3, p. 31, 1990.) • Magnetic Storage : --Recording medium is magnetized by recording head.
  9. 9. OPTICAL • Transmittance : --Aluminum oxide may be transparent, translucent, or opaque depending on the material structure. Adapted from Fig. 1.2, Callister 6e. (Specimen preparation, P.A. Lessing; photo by J. Telford.) single crystal polycrystal: low porosity polycrystal: high porosity
  10. 10. Classification of Materials Metals Ceramics & Glasses Polymers <ul><li>Insulators of e - and heat </li></ul><ul><li>Very flexible, deformable, low strength </li></ul><ul><li>Some transparent </li></ul><ul><li>Good corrosion resistance </li></ul><ul><li>Low resistance to heat </li></ul><ul><li>Low density </li></ul><ul><li>All plastics, Nylon, Rubber </li></ul><ul><li>Insulators of e - and heat </li></ul><ul><li>Hard, brittle, not deformable </li></ul><ul><li>Some transparent </li></ul><ul><li>Good corrosion resistance </li></ul><ul><li>Heat resistant </li></ul><ul><li>SiC, Si 3 N 4 , Al 2 O 3 ,BaTiO 3, YBCO Superconductors </li></ul><ul><li>Good conductors of e - and heat </li></ul><ul><li>Strong, deformable </li></ul><ul><li>Not transparent </li></ul><ul><li>Susceptible to chemical degradation in some atmospheres </li></ul><ul><li>High density </li></ul><ul><li>Fe, Steel, Cu, Al, Brass </li></ul>
  11. 11. Metals
  12. 12. Ceramics and Glasses
  13. 13. Polymers
  14. 14. Semi-Conductors Properties between conductor & insulator which can be modified by minor dopants. Si, GaAs Composites Engineered materials, combine best characteristics of metals, ceramics, and polymer Smart (Functional) Materials Shape memory alloys (NiTi), piezoeffect (PZT) magnetostriction (Terfenol-D) Sensors-actuators Advanced Materials Elements of IC, magnetic storage, LCDs, fiberoptics, thin films, nanoscale… Classification of Materials
  15. 15. Review <ul><li>Cite the general characteristics of the elements that are arrayed in each column of the periodic table. </li></ul><ul><li>Briefly describe ionic, covalent, metallic, hydrogen, and Van der Waal's bonds </li></ul><ul><li>Make a distinction between cations and anions . </li></ul><ul><li>Given the electronegativities of two elements, compute the percent ionic character of the bond that forms between them. </li></ul><ul><li>Know the basic crystal structures. </li></ul><ul><li>Know simple point defect types. </li></ul>
  16. 16. BOHR ATOM Nucleus: Z = # protons = 1 for hydrogen to 94 for plutonium N = # neutrons Atomic mass A ≈ Z + N Adapted from Fig. 2.1, Callister 6e.
  17. 17. ELECTRON ENERGY STATES • have discrete energy states • tend to occupy lowest available energy state. Electrons... Adapted from Fig. 2.5, Callister 6e.
  18. 18. STABLE ELECTRON CONFIGURATIONS • have complete s and p subshells • tend to be unreactive . Stable electron configurations... Adapted from Table 2.2, Callister 6e.
  19. 19. SURVEY OF ELEMENTS • Why? Valence (outer) shell usually not filled completely. • Most elements: Electron configuration not stable . Adapted from Table 2.2, Callister 6e.
  20. 20. THE PERIODIC TABLE • Columns: Similar Valence Structure Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. Adapted from Fig. 2.6, Callister 6e.
  21. 21. Ionic character and electronegativity Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond , 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. ELECTRONEGATIVITY Give up electrons Acquire electrons
  22. 22. IONIC BONDING • Occurs between + and - ions. <ul><li>• Requires electron transfer. </li></ul><ul><li>Predominant bonding in Ceramics. </li></ul>• Large difference in electronegativity required. • Example: NaCl Cations have large electronegativities, anions have small values. Cations give up electrons, anions acquire electrons. Cations are small, anions are large.
  23. 23. COVALENT BONDING • Requires shared electrons • Example: CH 4 C: has 4 valence e, needs 4 more H: has 1 valence e, needs 1 more Electronegativities are comparable. Adapted from Fig. 2.10, Callister 6e.
  24. 24. EXAMPLES: COVALENT BONDING • Molecules with nonmetals • Molecules with metals and nonmetals • Elemental solids (RHS of Periodic Table) • Compound solids (about column IVA ) Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond , 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
  25. 25. <ul><li>Hydrogen Bonding </li></ul><ul><li>Metallic Bonding </li></ul><ul><li>Van der Waals Bonding </li></ul>
  26. 26. SIMPLE CUBIC STRUCTURE (SC) • Rare due to poor packing (only Po has this structure) • Close-packed directions are cube edges. • Coordination # = 6 (# nearest neighbors) (Courtesy P.M. Anderson)
  27. 27. BODY CENTERED CUBIC STRUCTURE (BCC) • Coordination # = 8 Adapted from Fig. 3.2, Callister 6e. (Courtesy P.M. Anderson) • Close packed directions are cube diagonals. --Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.
  28. 28. FACE CENTERED CUBIC STRUCTURE (FCC) • Coordination # = 12 Adapted from Fig. 3.1(a), Callister 6e. (Courtesy P.M. Anderson) • Close packed directions are face diagonals. --Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.
  29. 29. HEXAGONAL CLOSE-PACKED STRUCTURE (HCP) • Coordination # = 12 • ABAB... Stacking Sequence • APF = 0.74 • 3D Projection • 2D Projection Adapted from Fig. 3.3, Callister 6e.
  30. 30. FCC STACKING SEQUENCE • ABCABC... Stacking Sequence • 2D Projection • FCC Unit Cell
  31. 31. STRUCTURE OF COMPOUNDS: NaCl • Compounds: Often have similar close-packed structures. • Close-packed directions --along cube edges. • Structure of Na Cl (Courtesy P.M. Anderson)
  32. 32. Self point defects
  33. 33. Dopant / Impurity point defects
  34. 34. SINGLE VS POLYCRYSTALS • Single Crystals -Properties vary with direction: anisotropic . -Example: the modulus of elasticity (E) in BCC iron: • Polycrystals -Properties may/may not vary with direction. -If grains are randomly oriented: isotropic . (E poly iron = 210 GPa) -If grains are textured , anisotropic. 200  m Data from Table 3.3, Callister 6e . (Source of data is R.W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials , 3rd ed., John Wiley and Sons, 1989.) Adapted from Fig. 4.12(b), Callister 6e . (Fig. 4.12(b) is courtesy of L.C. Smith and C. Brady, the National Bureau of Standards, Washington, DC [now the National Institute of Standards and Technology, Gaithersburg, MD].)
  35. 35. SUMMARY • Basic crystal structures, atomic coordination, atom sites, atom packing, and point defects are known. Chapter sections: 12.1-4 Review Chapter sections from last term: 1, 2.3-2.8, 3.1-3.4, 4.1-4.3 Reading for next class

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