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Materials and their Properties

Materials and their Properties. Chapter 11. Great Idea: A material’s properties result from its constituent atoms and the arrangements of chemical bonds that hold those atoms together. Materials and the Modern World. Materials define the technical sophistication of a society:

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Materials and their Properties

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  1. Materials and their Properties Chapter 11 Great Idea: A material’s properties result from its constituent atoms and the arrangements of chemical bonds that hold those atoms together

  2. Materials and the Modern World • Materials define the technical sophistication of a society: • Stone Age, Iron Age, Bronze Age, … Electronic Age • Chemists’ contributions: • Number of materials has increased by a thousandfold in the past two centuries. • Properties of Materials • Constituent atoms • Arrangement of atoms • Type of bonding of atoms

  3. The Strength of Material • Strength: ability to resist changes in shape • Different kinds of Strength • Crushing: Compressive • Pulling apart: Tensile • Twisting: Shear • Elastic Limit: a material stops resisting external forces and begins to bend, break, or tear - Permanently change the object • Strength depends on • Kinds of atoms • Way they are arranged • Kind of chemical bonding • Strongest arrangement: • short sticks with triangle patterns Girder used in buildings and bridges

  4. Composite Materials • Composite materials • Combination of materials to Increase strength Examples: Plywood Reinforces concrete with steel rods Various composite materials used in automobiles (Safety and light weight are important to consider): windshields, tires, bodies…

  5. Electrical Properties of Materials • Electrical Conductors • Electrons flow freely • Electrical resistance: • Electrons collide with ions and lost energy to heat • Electrical conductance: • Inverse of resistance • Electrical Insulators • Electrons are bound tightly to atoms (by ionic or covalent bonds) and few are free to move. No electricity flows through them

  6. Semiconductors Neither good conductors nor perfect insulators • Example: Silicon • conduction electrons (-) • holes (+)

  7. More About Semiconductors Example: Silicon Doping: addition of minor impurity n-type (electrons) p-type (holes)

  8. Superconductors Superconductivity and Critical Temperature (Tc): Materials become completely absent of electrical resistance below certain cold temperature (electrons move without losing energy) Why? Electrons form pairs; Whole collection of electrons interlock. Important applications of strong magnetic fields Magnetic high speed floating train MRI image

  9. Searching for New Superconductors BeforeMid-1980s: Metals, Cooled with liquid Helium (4K) 1986, Karl Alex Muller and George Bednorz, IMB’ Zurich, Switzerland lab. Oxides: rocks and ceramics, 30 K Currently: 160 K, High-Tc superconductors Liquid Nitrogen (77k = -196C): rich resources, low prices

  10. Magnetic Properties of Materials • Magnetic field • Due to electrical current • Electrons spinning • Arrangement of atomic magnets determines level of magnetism a. non-magnetic b. Ferromagnetic domains c. Permanent magnetic

  11. Diodes • Diode • Combination of p- and n-type semiconductors • One-way gate

  12. Transistor: Creating Electronic Age • Transistor: invented by John Bardeen, Walter Brattain, and William Schockley in Dec. 1947 • Control flow of electrons • Emitter • Base • Collector • Function • Signal amplifier • Electron switch • Uses • Cell phone • Computer

  13. Microchips and Information Revolution • Microchip • Complex array of p- and n-type semiconductors • Integrated circuit • Design • Layers interconnected

  14. Moore’s Law • The ever-increasing information capacity of computers Trend in History of Computer Hardware (compared with growth of transistor count for Intel Processors)

  15. Information • The binary digit or bit • Two possible answers to a simple question • yes or no, • on or off, • 1 or 0 • 8 bits= 1 byte

  16. Computers • Computer • Stores and manipulates information • Central Processing Unit (CPU) • Nanotechnology

  17. Homework Reading: pp218-227 Self Quizzes 1-20 More Exercises: 1,3,4,13-18,21-24

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