THE NATURE OF MATERIALS <ul><li>Atomic Structure and the Elements </li></ul><ul><li>Bonding between Atoms and Molecules </...
Importance of Materials in Manufacturing <ul><li>Manufacturing is a transformation process  </li></ul><ul><ul><li>It is th...
Element Groupings <ul><li>The elements can be grouped into families and relationships established between and within the f...
Periodic Table
Atomic Structure and the Elements <ul><li>The basic structural unit of matter is the atom  </li></ul><ul><ul><li>Each atom...
Simple Model of Atomic Structure for Several Atoms <ul><li>(a) Hydrogen, (b) helium, (c) fluorine, (d) neon, and (e) sodiu...
Bonding between Atoms and Molecules <ul><li>Atoms are held together in molecules by various types of bonds </li></ul><ul><...
Primary Bonds <ul><li>Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons  </li></...
Ionic Bonding <ul><li>Atoms of one element give up their outer electron(s), which are in turn attracted to atoms of some o...
Covalent Bonding <ul><li>Electrons are shared (as opposed to transferred) between atoms in their outermost shells to achie...
Two Examples of  Covalent Bonding
Metallic Bonding <ul><li>Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the...
Secondary Bonds <ul><li>Whereas primary bonds involve atom‑to‑atom attractive forces, secondary bonds involve attraction f...
Dipole Forces <ul><li>Arise in a molecule comprised of two atoms with equal and opposite electrical charges </li></ul><ul>...
London Forces <ul><li>Attractive force between non-polar molecules, i.e., atoms in molecule do not form dipoles </li></ul>...
Hydrogen Bonding <ul><li>Occurs in molecules containing hydrogen atoms covalently bonded to another atom (e.g., H 2 O) </l...
Macroscopic Structures of Matter <ul><li>Atoms and molecules are the building blocks of a more macroscopic structure of ma...
Crystalline Structure <ul><li>Structure in which atoms are located at regular and recurring positions in three dimensions ...
Three Crystal Structures in Metals <ul><li>Three types of crystal structure: (a) body-centered cubic, (b) face-centered cu...
Crystal Structures for Common Metals  <ul><li>Room temperature crystal structures for some of the common metals: </li></ul...
Imperfections (Defects) in Crystals <ul><li>Imperfections often arise due to inability of solidifying material to continue...
Point Defects <ul><li>Imperfections in crystal structure involving either a single atom or a small number of atoms </li></...
Line Defects  <ul><li>Connected group of point defects that forms a line in the lattice structure </li></ul><ul><li>Most i...
Edge Dislocation <ul><li>Edge of an extra plane of atoms that exists in the lattice </li></ul>
Screw Dislocation <ul><li>Spiral within the lattice structure wrapped around an imperfection line, like a screw is wrapped...
Surface Defects  <ul><li>Imperfections that extend in two directions to form a boundary  </li></ul><ul><li>Examples: </li>...
Elastic Strain <ul><li>When a crystal experiences a gradually increasing stress, it first deforms elastically </li></ul>De...
Plastic Strain <ul><li>If the stress is higher than forces holding atoms in their lattice positions, then a permanent shap...
Effect of Dislocations on Strain <ul><li>In the series of diagrams, the movement of the dislocation allows deformation to ...
Slip on a Macroscopic Scale <ul><li>Slip occurs many times over throughout the metal when subjected to a deforming load, t...
Twinning <ul><li>A second mechanism of plastic deformation in which atoms on one side of a plane (the twinning plane) are ...
Twinning <ul><li>After </li></ul>
Polycrystalline Nature of  Metals <ul><li>A block of metal may contain millions of individual crystals, called grains  </l...
Grains and Grain Boundaries in Metals <ul><li>How do polycrystalline structures form?  </li></ul><ul><ul><li>As a volume o...
Noncrystalline (Amorphous) Structures <ul><li>Water and air have noncrystalline structures </li></ul><ul><li>A metal loses...
Features of Noncrystalline Structures <ul><li>Two features differentiate noncrystalline (amorphous) from crystalline mater...
Crystalline versus Noncrystalline Structures of Materials <ul><li>Difference in structure between: (a) crystalline and (b)...
Volumetric Effects <ul><li>Characteristic change in volume for a pure metal (a crystalline structure), compared to same vo...
Summary: Characteristics of Metals <ul><li>Crystalline structures in the solid state, almost without exception  </li></ul>...
Summary: Characteristics of Ceramics <ul><li>Most ceramics have crystalline structures, while glass (SiO 2 ) is amorphous ...
Summary: Characteristics of Polymers <ul><li>Many repeating  mers  in molecule held together by covalent bonding </li></ul...
Upcoming SlideShare
Loading in …5
×

Ch02

1,901 views

Published on

Published in: Technology, Education
0 Comments
3 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,901
On SlideShare
0
From Embeds
0
Number of Embeds
105
Actions
Shares
0
Downloads
186
Comments
0
Likes
3
Embeds 0
No embeds

No notes for slide

Ch02

  1. 1. THE NATURE OF MATERIALS <ul><li>Atomic Structure and the Elements </li></ul><ul><li>Bonding between Atoms and Molecules </li></ul><ul><li>Crystalline Structures </li></ul><ul><li>Noncrystalline (Amorphous) Structures </li></ul><ul><li>Engineering Materials </li></ul>
  2. 2. Importance of Materials in Manufacturing <ul><li>Manufacturing is a transformation process </li></ul><ul><ul><li>It is the material that is transformed </li></ul></ul><ul><ul><li>And it is the behavior of the material when subjected to the forces, temperatures, and other parameters of the process that determines the success of the operation </li></ul></ul>
  3. 3. Element Groupings <ul><li>The elements can be grouped into families and relationships established between and within the families by means of the Periodic Table </li></ul><ul><ul><li>Metals occupy the left and center portions of the table </li></ul></ul><ul><ul><li>Nonmetals are on right </li></ul></ul><ul><ul><li>Between them is a transition zone containing metalloids or semi‑metals </li></ul></ul>
  4. 4. Periodic Table
  5. 5. Atomic Structure and the Elements <ul><li>The basic structural unit of matter is the atom </li></ul><ul><ul><li>Each atom is composed of a positively charged nucleus, surrounded by a sufficient number of negatively charged electrons so the charges are balanced </li></ul></ul><ul><ul><li>More than 100 elements, and they are the chemical building blocks of all matter </li></ul></ul>
  6. 6. Simple Model of Atomic Structure for Several Atoms <ul><li>(a) Hydrogen, (b) helium, (c) fluorine, (d) neon, and (e) sodium </li></ul>
  7. 7. Bonding between Atoms and Molecules <ul><li>Atoms are held together in molecules by various types of bonds </li></ul><ul><ul><li>Primary bonds - generally associated with formation of molecules </li></ul></ul><ul><ul><li>Secondary bonds - generally associated with attraction between molecules </li></ul></ul><ul><li>Primary bonds are much stronger than secondary bonds </li></ul>
  8. 8. Primary Bonds <ul><li>Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons </li></ul><ul><li>Following forms: </li></ul><ul><ul><li>Ionic </li></ul></ul><ul><ul><li>Covalent </li></ul></ul><ul><ul><li>Metallic </li></ul></ul>
  9. 9. Ionic Bonding <ul><li>Atoms of one element give up their outer electron(s), which are in turn attracted to atoms of some other element to increase electron count in the outermost shell to eight </li></ul>
  10. 10. Covalent Bonding <ul><li>Electrons are shared (as opposed to transferred) between atoms in their outermost shells to achieve a stable set of eight </li></ul>
  11. 11. Two Examples of Covalent Bonding
  12. 12. Metallic Bonding <ul><li>Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the entire block </li></ul>
  13. 13. Secondary Bonds <ul><li>Whereas primary bonds involve atom‑to‑atom attractive forces, secondary bonds involve attraction forces between molecules </li></ul><ul><li>No transfer or sharing of electrons </li></ul><ul><li>Bonds are weaker than primary bonds </li></ul><ul><li>Three forms: </li></ul><ul><ul><li>Dipole forces </li></ul></ul><ul><ul><li>London forces </li></ul></ul><ul><ul><li>Hydrogen bonding </li></ul></ul>
  14. 14. Dipole Forces <ul><li>Arise in a molecule comprised of two atoms with equal and opposite electrical charges </li></ul><ul><li>Each molecule therefore forms a dipole that attracts other molecules </li></ul>
  15. 15. London Forces <ul><li>Attractive force between non-polar molecules, i.e., atoms in molecule do not form dipoles </li></ul><ul><li>However, due to rapid motion of electrons in orbit, temporary dipoles form when more electrons are on one side </li></ul>
  16. 16. Hydrogen Bonding <ul><li>Occurs in molecules containing hydrogen atoms covalently bonded to another atom (e.g., H 2 O) </li></ul><ul><li>Since electrons to complete shell of hydrogen atom are aligned on one side of nucleus, opposite side has a net positive charge that attracts electrons in other molecules </li></ul>
  17. 17. Macroscopic Structures of Matter <ul><li>Atoms and molecules are the building blocks of a more macroscopic structure of matter </li></ul><ul><li>When materials solidify from the molten state, they tend to close ranks and pack tightly, arranging themselves into one of two structures: </li></ul><ul><ul><li>Crystalline </li></ul></ul><ul><ul><li>Noncrystalline </li></ul></ul>
  18. 18. Crystalline Structure <ul><li>Structure in which atoms are located at regular and recurring positions in three dimensions </li></ul><ul><li>Unit cell - basic geometric grouping of atoms that is repeated </li></ul><ul><li>The pattern may be replicated millions of times within a given crystal </li></ul><ul><li>Characteristic structure of virtually all metals, as well as many ceramics and some polymers </li></ul>
  19. 19. Three Crystal Structures in Metals <ul><li>Three types of crystal structure: (a) body-centered cubic, (b) face-centered cubic, and (c) hexagonal close-packed </li></ul>
  20. 20. Crystal Structures for Common Metals <ul><li>Room temperature crystal structures for some of the common metals: </li></ul><ul><ul><li>Body‑centered cubic (BCC) </li></ul></ul><ul><ul><ul><li>Chromium, Iron, Molybdenum, Tungsten </li></ul></ul></ul><ul><ul><li>Face‑centered cubic (FCC) </li></ul></ul><ul><ul><ul><li>Aluminum, Copper, Gold, Lead, Silver, Nickel </li></ul></ul></ul><ul><ul><li>Hexagonal close‑packed (HCP) </li></ul></ul><ul><ul><ul><li>Magnesium, Titanium, Zinc </li></ul></ul></ul>
  21. 21. Imperfections (Defects) in Crystals <ul><li>Imperfections often arise due to inability of solidifying material to continue replication of unit cell, e.g., grain boundaries in metals </li></ul><ul><li>Imperfections can also be introduced purposely; e.g., addition of alloying ingredient in metal </li></ul><ul><li>Types of defects: (1) point defects, (2) line defects, (3) surface defects </li></ul>
  22. 22. Point Defects <ul><li>Imperfections in crystal structure involving either a single atom or a small number of atoms </li></ul>Point defects: (a) vacancy, (b) ion‑pair vacancy, (c) interstitialcy, (d) displaced ion (Frenkel Defect).
  23. 23. Line Defects <ul><li>Connected group of point defects that forms a line in the lattice structure </li></ul><ul><li>Most important line defect is a dislocation , which can take two forms: </li></ul><ul><ul><li>Edge dislocation </li></ul></ul><ul><ul><li>Screw dislocation </li></ul></ul>
  24. 24. Edge Dislocation <ul><li>Edge of an extra plane of atoms that exists in the lattice </li></ul>
  25. 25. Screw Dislocation <ul><li>Spiral within the lattice structure wrapped around an imperfection line, like a screw is wrapped around its axis </li></ul>
  26. 26. Surface Defects <ul><li>Imperfections that extend in two directions to form a boundary </li></ul><ul><li>Examples: </li></ul><ul><ul><li>External: the surface of a crystalline object is an interruption in the lattice structure </li></ul></ul><ul><ul><li>Internal: grain boundaries are internal surface interruptions </li></ul></ul>
  27. 27. Elastic Strain <ul><li>When a crystal experiences a gradually increasing stress, it first deforms elastically </li></ul>Deformation of a crystal structure: (a) original lattice: (b) elastic deformation, no permanent change in positions of atoms
  28. 28. Plastic Strain <ul><li>If the stress is higher than forces holding atoms in their lattice positions, then a permanent shape change occurs </li></ul>Plastic deformation (slip), in which atoms in the crystal lattice structure are forced to move to new &quot;homes“
  29. 29. Effect of Dislocations on Strain <ul><li>In the series of diagrams, the movement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice </li></ul>
  30. 30. Slip on a Macroscopic Scale <ul><li>Slip occurs many times over throughout the metal when subjected to a deforming load, thus causing it to exhibit its macroscopic behavior in the stress-strain relationship </li></ul><ul><li>Dislocations are a good‑news‑bad‑news situation </li></ul><ul><ul><li>Good news in manufacturing – the metal is easier to form </li></ul></ul><ul><ul><li>Bad news in design – the metal is not as strong as the designer would like </li></ul></ul>
  31. 31. Twinning <ul><li>A second mechanism of plastic deformation in which atoms on one side of a plane (the twinning plane) are shifted to form a mirror image of the other side </li></ul><ul><li>Before </li></ul>
  32. 32. Twinning <ul><li>After </li></ul>
  33. 33. Polycrystalline Nature of Metals <ul><li>A block of metal may contain millions of individual crystals, called grains </li></ul><ul><li>Such a structure is called polycrystalline </li></ul><ul><ul><li>Each grain has its own unique lattice orientation </li></ul></ul><ul><ul><li>But collectively, the grains are randomly oriented in the block </li></ul></ul>
  34. 34. Grains and Grain Boundaries in Metals <ul><li>How do polycrystalline structures form? </li></ul><ul><ul><li>As a volume of metal cools from the molten state and begins to solidify, individual crystals nucleate at random positions and orientations throughout the liquid </li></ul></ul><ul><ul><li>These crystals grow and finally interfere with each other, forming at their interface a surface defect ‑ a grain boundary , which are transition zones, perhaps only a few atoms thick </li></ul></ul>
  35. 35. Noncrystalline (Amorphous) Structures <ul><li>Water and air have noncrystalline structures </li></ul><ul><li>A metal loses its crystalline structure when melted </li></ul><ul><li>Some engineering materials have noncrystalline forms in their solid state </li></ul><ul><ul><li>Glass </li></ul></ul><ul><ul><li>Many plastics </li></ul></ul><ul><ul><li>Rubber </li></ul></ul>
  36. 36. Features of Noncrystalline Structures <ul><li>Two features differentiate noncrystalline (amorphous) from crystalline materials: </li></ul><ul><ul><li>Absence of long‑range order in molecular structure </li></ul></ul><ul><ul><li>Differences in melting and thermal expansion characteristics </li></ul></ul>
  37. 37. Crystalline versus Noncrystalline Structures of Materials <ul><li>Difference in structure between: (a) crystalline and (b) noncrystalline materials </li></ul><ul><li>Crystal structure is regular, repeating; noncrystalline structure is less tightly packed and random </li></ul><ul><li>(a) (b) </li></ul>
  38. 38. Volumetric Effects <ul><li>Characteristic change in volume for a pure metal (a crystalline structure), compared to same volumetric changes in glass (a noncrystalline structure) </li></ul>
  39. 39. Summary: Characteristics of Metals <ul><li>Crystalline structures in the solid state, almost without exception </li></ul><ul><li>BCC, FCC, or HCP unit cells </li></ul><ul><li>Atoms held together by metallic bonding </li></ul><ul><li>Properties: high strength and hardness, high electrical and thermal conductivity </li></ul><ul><li>FCC metals are generally ductile </li></ul>
  40. 40. Summary: Characteristics of Ceramics <ul><li>Most ceramics have crystalline structures, while glass (SiO 2 ) is amorphous </li></ul><ul><li>Molecules characterized by ionic or covalent bonding, or both </li></ul><ul><li>Properties: high hardness and stiffness, electrically insulating, refractory, and chemically inert </li></ul>
  41. 41. Summary: Characteristics of Polymers <ul><li>Many repeating mers in molecule held together by covalent bonding </li></ul><ul><li>Polymers usually carbon plus one or more other elements: H, N, O, and Cl </li></ul><ul><li>Amorphous (glassy) structure or mixture of amorphous and crystalline </li></ul><ul><li>Properties: low density, high electrical resistivity, and low thermal conductivity, strength and stiffness vary widely </li></ul>

×