EDWARD'S LECTURE NOTES:
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C O U R S E
Materials Science: 10 Things Every Engineer Should Know
James Shackelford, University of California, Irvine
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C O U R S E L E C T U R E The Six Categories of Engineering Materials Notes taken on January 8, 2016 by Edward Tanguay |
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six categories of engineering materials
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nearly all materials used for modern applications come from these six categories
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1. metals
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metallic bond
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adjacent atoms share electrons in a non-directional way
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metal pan
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can't see through it
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electrons that provide the metallic bonding are reflecting any proton light rays from the environment
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gives us the characteristic shiny luster
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can conduct electricity, since bonding electrons are mobile
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power cord
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metal is providing the conductivity
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polymer sheathing that is providing the safety and insulation
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2. polymers
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covalent bond
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directional bond
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electron sharing between adjacent atoms
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have a stable balance
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plastic spatula
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good structural integrity
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convenient
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light-weight
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carbon-to-hydrogen bonding
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covalent
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electrons are being shared by the two adjacent atoms
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electrons are thus spoken for, good insulator
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3. ceramics
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ionic bond
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non-directional bond
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electron sharing from one atom to another
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involves the electrostatic attraction between oppositely charged ions
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atoms that have lost one or more electrons (known as cations) and atoms that have gained one or more electrons (known as anions)
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from a metallic cation to a negative anion, very often oxygen
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Coulombic forces
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the magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them
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common ceramic coffee mug
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electrons are spoken for, therefore electrical insulating
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first three categories are based on the three different kind of electron bonding: metallic, covalent, and ionic
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4. glass
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a subset of ceramics
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the key distinction between the ceramic and glass
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glass: random atomic arrangement of ions
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ceramic: crystalline formation
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common drinking glass
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optically transparent
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because of the nature of the ionic bonding
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silicon ions and oxygen ions, a common silicate material
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5. fiberglass
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best of both worlds
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the ductility of a polymer
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ductility: when a solid material stretches under tensile stress
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like the plastic spatula
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harder structure
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from microscopic glass fibers
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a few microns in diameter
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stacking chairs
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fiberglass
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6. semiconductors
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small piece of silicon
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microscopic and submicroscopic
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can control the conductivity in a very powerful way